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The investigation of aluminum gallium nitride/gallium nitride high electron mobility transistor (AlGaN/GaN HEMT) devices with a dual‐metal gate (DMG) structure encompasses both electrical and thermal characteristics. As efforts to enhance heat dissipation progress, there is a concurrent exploration of novel semiconductor materials boasting high thermal conductivity, like boron arsenide and phosphide. Combining these materials into a model and measuring their interface achieves efficient energy transport. Minimizing the self‐heating impact in AlGaN/GaN HEMTs is essential for enhancing device efficiency. This research exposes the heterogenous combination of boron arsenide and phosphide cooling substrates with metals, GaN semiconductors and HEMT. In this research, the autoencoder deep neural network techniques in GaN HEMT for self‐heat reduction is driven by the ability to effectively analyze and model the thermal behavior of the device. Autoencoders learn complex relationships within temperature data and identify patterns associated with self‐heating. By leveraging these learned representations, the deep neural network optimizes control strategies to mitigate self‐heating effects in GaN HEMT devices, ultimately contributing to improved thermal management and enhanced overall performance. In this research, the use of genetic algorithms in GaN HEMT aims to optimize device parameters systematically, to minimize self‐heating effects and enhance overall thermal performance. The structure also enhances electron mobility within the channel. Results show DMG structures, exhibiting higher saturation output currents and transconductance despite self‐heating. The DMG exhibits a maximum gm value of 0.164 S/mm, which is 10% higher significantly enhancing GaN‐based HEMTs for improved reliability and efficiency in various applications. [ABSTRACT FROM AUTHOR]

The aluminum gallium nitride (AlGaN)-based deep-ultraviolet light-emitting diode (DUV-LED) has been a prominent device due to its contribution in various fields. The electron blocking layer (EBL) is an additional layer in the epitaxy of the DUV-LED with the aim of reducing the overflow of electrons and improving the hole injection, consequently increasing the performance of the DUV-LED. However, the threshold of the EBL thickness and its influence on the electrical and optical properties is still not fully understood. Hence, the purpose of this research is to investigate the effects of varying the EBL thickness, ranging from 5 nm up to 60 nm, and investigate the threshold of EBL thickness for the AlGaN-based DUV-LED. The analysis includes the internal quantum efficiency (IQE), luminescence spectrum, band diagram behavior, and the current density of the carrier. It is found that EBL thickness of 15 nm produces the highest IQE (39.69%) for the DUV-LED with a single quantum well structure, where the wavelength emitted is ~ 257 nm, which is within the ultraviolet C (UVC) range. [ABSTRACT FROM AUTHOR]

Semi‐floating gate field‐effect transistors (SFG‐FETs) based on 2D materials have received much attention due to their unique optoelectronic characteristics, potential applications in near‐memory computing and constructing sensing‐memory‐processing units. Here, the non‐volatile and gate‐controlled multistate photovoltaic response of a WSe2/h‐BN/graphene SFG‐FET is investigated both in experimental and theoretical aspects. Due to the ambipolar carrier transport of WSe2 channel, both electrons and holes can be stored in the graphene floating gate layer, which results in two evident memory windows on the round sweep transfer characteristic curve. Different charge‐stored states of the SFG layer enable the channel to form a lateral junction that can be adjusted by the gate voltage, which leads to the gate‐controlled multistate photovoltaic response. A theoretical model is implemented to explain the memory and the multistate photovoltaic response behaviors in a quasi‐quantitative level. The relationship between the charge‐stored states in the SFG and the photo‐response, as well as its dependence on the gate voltage are systematically analyzed. These research results provide a reliable way for realizing high‐performance multi‐functional photodetectors based on SFG‐FETs and for thorough understanding the complicated optoelectronic behaviors of SFG‐FETs. [ABSTRACT FROM AUTHOR]

We have examined the origins of polytype selection during metal-mediated molecular-beam epitaxy of GaN nanowires (NWs). High-angle annular dark-field scanning transmission electron microscopy reveals [111]-oriented zinc blende (ZB) NWs and [0001]-oriented wurtzite (WZ) NWs, with SixNy at the interface between individual NWs and the Si (001) substrate. Quantitative energy dispersive x-ray spectroscopy reveals a notably higher Si concentration of 7.0% ± 2.3% in zinc blende (ZB) NWs than 2.3% ± 1.2% in wurtzite (WZ) NWs. Meanwhile, density functional theory calculations show that incorporation of 8 at. % Si on the Ga sublattice inverts the difference in formation energies between WZ and ZB GaN, such that the ZB polytype of GaN is stabilized. This identification of Si and other ZB polytype stabilizers will enable the development of polytype heterostructures in a wide variety of WZ-preferring compounds. [ABSTRACT FROM AUTHOR]

Herein, a high‐quality In0.1Al0.5Ga0.4N/GaN three‐channel (TC) heterostructure and the high‐electron‐mobility transistor (HEMT) based on it are proposed and investigated. The quaternary nitrides offer additional flexibility in adjusting the lattice constant and bandgap, enabling the achievement of a nearly strain‐free high‐Al‐content barrier. By stacking three In0.1Al0.5Ga0.4N/GaN heterostructures, a high 2D electron gas density of 2.59 × 1013 cm−2 and a high electron mobility of 1707 cm2 V−1 s−1 are achieved. As compared with the AlGaN/GaN TC heterostructure, the In0.1Al0.5Ga0.4N/GaN TC heterostructure reduces the sheet resistance by 39%, resulting in a 40 % reduction in the on‐resistance of the TC HEMT. Additionally, the inverse piezoelectric effect of the In0.1Al0.5Ga0.4N/GaN TC‐HEMT is investigated by negative‐gate voltage bias step‐stress experiments. During the stress experiments, no irreversible degradation is observed in the In0.1Al0.5Ga0.4N/GaN TC‐HEMT, while the AlGaN/GaN TC‐HEMT exhibits a significant deterioration beyond the critical voltage. The reliability related to the inverse piezoelectric effect of the devices can be further improved due to the lower stress in the lattice‐matched quaternary barrier. [ABSTRACT FROM AUTHOR]

Group-III nitrides have transformed solid-state lighting and are strategically positioned to revolutionize high-power and high-frequency electronics. To drive this development forward, a deep understanding of fundamental material properties, such as charge carrier behavior, is essential and can also unveil new and unforeseen applications. This underscores the necessity for novel characterization tools to study group-III nitride materials and devices. The optical Hall effect (OHE) emerges as a contactless method for exploring the transport and electronic properties of semiconductor materials, simultaneously offering insights into their dielectric function. This non-destructive technique employs spectroscopic ellipsometry at long wavelengths in the presence of a magnetic field and provides quantitative information on the charge carrier density, sign, mobility, and effective mass of individual layers in multilayer structures and bulk materials. In this paper, we explore the use of terahertz (THz) OHE to study the charge carrier properties in group-III nitride heterostructures and bulk material. Examples include graded AlGaN channel high-electron-mobility transistor (HEMT) structures for high-linearity devices, highlighting the different grading profiles and their impact on the two-dimensional electron gas (2DEG) properties. Next, we demonstrate the sensitivity of the THz OHE to distinguish the 2DEG anisotropic mobility parameters in N-polar GaN/AlGaN HEMTs and show that this anisotropy is induced by the step-like surface morphology. Finally, we present the temperature-dependent results on the charge carrier properties of 2DEG and bulk electrons in GaN with a focus on the effective mass parameter and review the effective mass parameters reported in the literature. These studies showcase the capabilities of the THz OHE for advancing the understanding and development of group-III materials and devices. [ABSTRACT FROM AUTHOR]

Aluminum gallium nitride/gallium nitride multi-channel superlattice devices are receiving increasing attention as a new paradigm for driving the power density of gallium nitride based transistors toward their theoretical limit. However, the superior electrical performance of superlattice-based transistors is currently limited by excessive Joule-heating. This Letter evaluates what impact the number of superlattice channels and the buffer layer composition has on the reduction of the thermal resistance, i.e., Joule heating, of AlGaN/GaN superlattice devices. A record low thermal resistance (12.51 ± 0.34 K mm W−1) was measured via scanning thermal microscopy for non-castellated superlattice AlGaN/GaN devices with a 100 μm channel width. Overall, the use of a thin gallium nitride buffer layer, in place of a thick aluminum gallium nitride layer, reduced the buffer thermal resistance enabling the accommodation of more superlattice channels (10 vs 6), therefore augmenting the maximum power density of these devices. The superlattice device proposed here not only provides an enhanced thermal dissipation solution for high power density radio frequency electronics, but it also has the benefit of fewer fabrication steps in comparison with previously reported castellated multichannel devices. [ABSTRACT FROM AUTHOR]

Eco‐friendly and low‐cost aluminum gallium nitride (AlGaN) for the epitaxial growth of ultraviolet‐B (UVB) light‐emitting diodes (LEDs) on c‐Sapphire has the possibility of high external‐quantum efficiency (EQE). In this review paper a special growth techniques for 50% relaxed and 4 μm thick AlGaN buffer layer underneath the multi‐quantum wells (MQWs) are challenged to achieve a maximum internal‐quantum efficiency of 50–57% in 310–290 nm band UVB LEDs. The influence of a thin "Valley" layer in p‐type multi‐quantum barrier electron‐blocking layer on 2D hole generation and injection via intraband tunneling was attempted. Finally, the influence of soft polarized Mg‐doped p‐type Al‐graded AlGaN hole injection layer assisted by excimer laser annealing for better hole injection toward the MQWs was investigated and quite high hole concentration of 2 × 1016 cm−3 and resistivity of 24 Ω‐cm at room temperature was achieved. Consequently, the EQE of transparent 310 and 304 nm UVB LEDs, respectively, reached to a confirmed world record values of ≈5% and ≈10% with light powers of 29 and 40 mW on wafer. This EQE value can surpass 21% if flip‐chip, nanoPSS, photonic crystal, and lens with highly reflective p‐electrodes are incorporated in LED. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the Al2O3/GaN critical buried interface of the next generation of gallium nitride (GaN)‐based transistors using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and hard X‐ray photoelectron spectroscopy (HAXPES). Results highlight that gallium oxidation at this interface is enhanced when increasing the Al2O3 thickness from 3 up to 20 nm. Gallium oxidation is reduced when using both O3 and H2O as oxidant precursors, compared with only H2O during the growth of Al2O3. In addition, the O3/H2O‐based Al2O3 favors a reduction of contaminants such as hydrogen and carbon but enhances the presence of halides (Cl− and F−) at this Al2O3/GaN interface. [ABSTRACT FROM AUTHOR]

The utilization of optical antennas for active control of far-field radiation at the subwavelength scale is crucial in various scientific and technological applications. We propose a thermally tunable disk design of indium tin oxide (ITO) and aluminum gallium nitride ( Al 0.18 Ga 0.82 As ), enabling a switch between absorption and scattering. Furthermore, the control of far-field radiation pattern can be easily realized by combining ITO and Al 0.18 Ga 0.82 As to enhance or suppress emission. Our results demonstrate that hybrid structures can be dynamically tuned with temperature variations. In the proposed design, a frequency is achieved at the wavelength of 1240 nm. The thermal tunability of hybrid structures introduces new multifunctional possibilities for light manipulation, thereby enhancing the potential applications of new devices in the near-infrared range. [ABSTRACT FROM AUTHOR]

GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) with scandium aluminum nitride Sc0.2Al0.8N/SiNX composite gate dielectric were demonstrated with improved device performance in terms of current density, on-resistance, breakdown voltage, gate leakage, and current collapse. GaN MIS-HEMTs with single-layer Sc0.2Al0.8N or SiNX were also fabricated as reference. Notably, the current collapse was reduced from ∼38.8% in GaN MIS-HEMTs with single-layer SiNX dielectric to ∼4.9% in the device with composite gate dielectric. The insertion of the thin SiNX layer can mitigate the surface damage due to the ScAlN sputtering process and significantly reduce the interface state density. Furthermore, the high valence band offset of Sc0.2Al0.8N/SiNX of 0.78 eV also plays a key role in the suppression of hole injection and gate leakage current. This work shows the effectiveness of the Sc0.2Al0.8N/SiNX composite gate dielectric and can serve as an important reference for future developments of high-performance reliable GaN HEMTs for power and RF electronics. [ABSTRACT FROM AUTHOR]

Silicon qubits based on specific SOI FinFETs and nanowire (NW) transistors have demonstrated promising quantum properties and the potential application of advanced Si CMOS devices for future quantum computing. In this paper, for the first time, the quantum transport characteristics for the next-generation transistor structure of a stack nanosheet (NS) FET and the innovative structure of a fishbone FET are explored. Clear structures are observed by TEM, and their low-temperature characteristics are also measured down to 6 K. Consistent with theoretical predictions, greatly enhanced switching behavior characterized by the reduction of off-state leakage current by one order of magnitude at 6 K and a linear decrease in the threshold voltage with decreasing temperature is observed. A quantum ballistic transport, particularly notable at shorter gate lengths and lower temperatures, is also observed, as well as an additional bias of about 1.3 mV at zero bias due to the asymmetric barrier. Additionally, fishbone FETs, produced by the incomplete nanosheet release in NSFETs, exhibit similar electrical characteristics but with degraded quantum transport due to additional SiGe channels. These can be improved by adjusting the ratio of the channel cross-sectional areas to match the dielectric constants. [ABSTRACT FROM AUTHOR]

Since its invention in the 1960s, one of the most significant evolutions of metal-oxide semiconductor field effect transistors (MOSFETs) would be the 3D version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During recent decades, the width of fin (Wfin) and the neighboring gate oxide width (tox) in FinFETs has shrunk from about 150 nm to a few nanometers. However, both widths seem to have been leveling off in recent years, owing to the limitation of lithography precision. Here, we show that by adapting the Penn model and Maxwell–Garnett mixing formula for a dielectric constant (κ) calculation for nanolaminate structures, FinFETs with two- and three-stage κ-graded stacked combinations of gate dielectrics with SiO2, Si3N4, Al2O3, HfO2, La2O3, and TiO2 perform better against the same structures with their single-layer dielectrics counterparts. Based on this, FinFETs simulated with κ-graded gate oxides achieved an off-state drain current (IOFF) reduced down to 6.45 × 10−15 A for the Al2O3: TiO2 combination and a gate leakage current (IG) reaching down to 2.04 × 10−11 A for the Al2O3: HfO2: La2O3 combination. While our findings push the individual dielectric laminates to the sub 1 nm limit, the effects of dielectric permittivity matching and κ-grading for gate oxides remain to have the potential to shed light on the next generation of nanoelectronics for higher integration and lower power consumption opportunities. [ABSTRACT FROM AUTHOR]

Light emitters based on the semiconductor alloy aluminum gallium nitride [(Al,Ga)N] have gained significant attention in recent years due to their potential for a wide range of applications in the ultraviolet (UV) spectral window. However, current state-of-the-art (Al,Ga)N light emitters exhibit very low internal quantum efficiencies (IQEs). Therefore, understanding the fundamental electronic and optical properties of (Al,Ga)N-based quantum wells is key to improving the IQE. Here, we target the electronic and optical properties of c-plane AlxGa1−xN/AlN quantum wells by means of an empirical atomistic tight-binding model. Special attention is paid to the impact of random alloy fluctuations on the results as well as the Al content x in the well. We find that across the studied Al content range (from 10% to 75% Al), strong hole wave function localization effects are observed. Additionally, with increasing Al content, electron wave functions may also start to exhibit carrier localization features. Overall, our investigations on the electronic structure of c-plane AlxGa1−xN/AlN quantum wells reveal that already random alloy fluctuations are sufficient to lead to (strong) carrier localization effects. Furthermore, our results indicate that random alloy fluctuations impact the degree of optical polarization in c-plane AlxGa1−xN quantum wells. We find that the switching from transverse electric to transverse magnetic light polarization occurs at higher Al contents in the atomistic calculation, which accounts for random alloy fluctuations, compared to the widely used virtual crystal approximation approach. This observation is important for light extraction efficiencies in (Al,Ga)N-based light emitting diodes operating in the deep UV. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) possesses a high critical electric field, allowing for thinner drift regions and lower resistances compared with current materials used for power semiconductor devices. However, high activation energies of impurity dopants like magnesium or silicon and high contact resistances impede the application of AlN for typical device concepts such as TrenchFET. This article aims to develop and investigate novel vertical device structures using an AlN drift region. To evade the aforementioned issues, polarization‐induced doping is applied to generate an effective charge concentration and to accomplish less resistive ohmic contacts. [ABSTRACT FROM AUTHOR]

Simulations of optical gain in aluminum gallium nitride (AlGaN) quantum wells are extended to the high charge carrier density regime required for achieving gain at 275 nm for UV laser diodes. Coulomb interaction is modeled using the 2nd Born approximation. We demonstrate good agreement with experimental data obtained through optical pumping, and predict gain spectra for electrical pumping. Special consideration is given to the contribution of higher bands in wide quantum wells.

Aluminum Gallium Nitride (AlGaN) ultraviolet‐C (UV‐C) micro‐light‐emitting diodes (microLEDs) offer significant advantages in terms of convenience, cost‐effectiveness, and environmental friendliness, positioning them as promising candidates for display applications. However, achieving the desired high efficiency and scalability for large displays with ultra‐fine pixels necessitates substantial progress beyond current experimental outcomes. This study showcases the application of AlGaN UV‐C microLED display panels and micro‐displays incorporating quantum dots (QDs) for color conversion. Sidewall treatment and atomic layer deposited (ALD) passivation effectively address dangling bonds and etching damages, leading to a notable enhancement of TM‐polarized light extraction efficiency (LEE). Moreover, dedicated strain modulation efforts successfully reduce the high Al content (over 50%) wafer bowling effect, facilitating the modularization of ultrafine‐pitch AlGaN UV‐C microLED panels. Consequently, the devices achieve a peak performance of over 5% external quantum efficiency (EQE) as the mesa size scales down to 3 μm. The highlighted 0.18‐inch UV‐C microLED display panels, featuring a 9 μm pixel size, are precisely controlled by a CMOS IC driver to achieve desired patterns. Serving as an efficient pumping source for perovskite quantum dots paper (PQDP), this UV‐C microLED display suggests the potential to revolutionize the full‐color display industry by providing an innovative and unconventional solution. [ABSTRACT FROM AUTHOR]

This work reports on the development of a multi-output deep learning (DL) model for simultaneous prediction of the figure of merits (I o n , G m , and V t h ) of a gallium nitride (GaN) based high electron mobility transistors (HEMTs) for various epitaxial structures. To generate an initial data set, 2160 GaN HEMTs have also been simulated by an experimentally validated simulation methodology. A generative adversarial network (GAN) has been also introduced in semiconductor device modeling to augment the training data set. The generated data set by GAN is found to be in good agreement with the initial data set with a Frechet Inception Distance score of 0.151. The final data set has seven dimensions, i.e., aluminum gallium nitride (AlGaN) thickness (t AlGaN ), aluminum content in AlGaN, doping in AlGaN, type of doping in AlGaN, I o n , G m , and V t h , where the first four are inputs and the last three are the outputs of the DL model. The DL model is developed with the possibility of reducing unnecessary use of technology computer-aided design simulations for similar types of problems as such simulations require huge computational resources, expertise, and development time to obtain output. Mean squared error and R-squared values for the predicted I o n , G m , and V t h are 59.69, 4.28, and 0.09, and 0.99, 0.99, and 0.97, respectively. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) nanostructures of aluminum nitride (AlN) and gallium nitride (GaN), called nanosheets, have a graphene-like atomic arrangement and represent novel materials with important upcoming applications in the fields of flexible electronics, optoelectronics, and strain engineering, among others. Knowledge of their mechanical behavior is key to the correct design and enhanced functioning of advanced 2D devices and systems based on aluminum nitride and gallium nitride nanosheets. With this background, the surface Young's and shear moduli of AlN and GaN nanosheets over a wide range of aspect ratios were assessed using the nanoscale continuum model (NCM), also known as the molecular structural mechanics (MSM) approach. The NCM/MSM approach uses elastic beam elements to represent interatomic bonds and allows the elastic moduli of nanosheets to be evaluated in a simple way. The surface Young's and shear moduli calculated in the current study contribute to building a reference for the evaluation of the elastic moduli of AlN and GaN nanosheets using the theoretical method. The results show that an analytical methodology can be used to assess the Young's and shear moduli of aluminum nitride and gallium nitride nanosheets without the need for numerical simulation. An exploratory study was performed to adjust the input parameters of the numerical simulation, which led to good agreement with the results of elastic moduli available in the literature. The limitations of this method are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) "fabricated to improve device radio frequency (RF) performance for Ka-band applications" are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load–pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications. [ABSTRACT FROM AUTHOR]

A technique is proposed for the formation of epitaxial films of silicon carbide, gallium nitride and aluminum nitride on the surfaces of non-planar silicon parts. Using this technique, a GaN/AlN/SiC/Si heterostructure was grown on the surface of a silicon ring. The samples were studied by scanning electron microscopy, as well as by Raman and energy-dispersive spectroscopy. It is shown that the preliminary deposition of a SiC layer on silicon by the atom-substitution method in which (111) facets are inevitably being formed regardless of the local crystallographic orientation of the substrate surface makes it possible to efficiently grow on silicon parts subsequent layers of III-nitrides of both the wurtzite and sphalerite types. [ABSTRACT FROM AUTHOR]

Aluminum Gallium Nitride (AlGaN) ultraviolet‐C (UV‐C) micro‐light‐emitting diodes (microLEDs) offer significant advantages in terms of convenience, cost‐effectiveness, and environmental friendliness, positioning them as promising candidates for display applications. However, achieving the desired high efficiency and scalability for large displays with ultra‐fine pixels necessitates substantial progress beyond current experimental outcomes. This study showcases the application of AlGaN UV‐C microLED display panels and micro‐displays incorporating quantum dots (QDs) for color conversion. Sidewall treatment and atomic layer deposited (ALD) passivation effectively address dangling bonds and etching damages, leading to a notable enhancement of TM‐polarized light extraction efficiency (LEE). Moreover, dedicated strain modulation efforts successfully reduce the high Al content (over 50%) wafer bowling effect, facilitating the modularization of ultrafine‐pitch AlGaN UV‐C microLED panels. Consequently, the devices achieve a peak performance of over 5% external quantum efficiency (EQE) as the mesa size scales down to 3 μm. The highlighted 0.18‐inch UV‐C microLED display panels, featuring a 9 μm pixel size, are precisely controlled by a CMOS IC driver to achieve desired patterns. Serving as an efficient pumping source for perovskite quantum dots paper (PQDP), this UV‐C microLED display suggests the potential to revolutionize the full‐color display industry by providing an innovative and unconventional solution. [ABSTRACT FROM AUTHOR]

This work develops self‐aligned top‐gate (SA‐TG) amorphous indium‐tin‐zinc oxide (ITZO) thin‐film transistors (TFT) with high‐k AlOx gate insulator based on oxygen‐plasma formed source/drain technique. The fabricated SA‐TG TFTs based on this technique demonstrate good electrical performance, such as source/drain resistivity of less than 0.005W cm, high field‐effect mobility of 35.2 cm 2 /Vs, and near‐zero turn‐on voltage. Additionally, the SA‐TG high‐k devices exhibiting short‐channel effects only when the channel length is scaled to ~0.8 μm and demonstrated strong stability when subjected to thermal and gate bias stress. [ABSTRACT FROM AUTHOR]

Terminal aluminium and gallium imides of the type K[(NON)M(NR)], bearing heteroatom substituents at R, have been synthesised via reactions of anionic aluminium(I) and gallium(I) reagents with silyl and boryl azides (NON=4,5‐bis(2,6‐diisopropyl‐anilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene). These systems vary significantly in their lability in solution: the N(SiiPr3) and N(Boryl) complexes are very labile, on account of the high basicity at nitrogen. Phenylsilylimido derivatives provide greater stabilization through the π‐acceptor capabilities of the SiR3 group. K[(NON)AlN(SitBuPh2)] offers a workable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. The silylimide species examined feature minimal π‐bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO‐1 orbitals effectively comprising orthogonal lone pairs centred at N. Reactivity‐wise, both aluminium and gallium silylimides can act as viable sources of nitride, [N]3−, with systems derived from either metal reacting with CO to afford cyanide complexes. By contrast, only the gallium system K[(NON)Ga{N(SiPh3)}] is capable of effecting a similar transformation with N2O to yield azide, N3−, via formal oxide/nitride metathesis. The aluminium systems instead generate RN3 via transfer of the imide fragment [RN]2−. [ABSTRACT FROM AUTHOR]

The nanotribological properties of aluminum gallium nitride (AlxGa1−xN) epitaxial films grown on low-temperature-grown GaN/AlN/Si substrates were investigated using a nanoscratch system. It was confirmed that the Al compositions played an important role, which was directly influencing the strength of the bonding forces and the shear resistance. It was verified that the measured friction coefficient (μ) values of the AlxGa1−xN films from the Al compositions (where x = 0.065, 0.085, and 0.137) were in the range of 0.8, 0.5, and 0.3, respectively, for Fn = 2000 μN and 0.12, 0.9, and 0.7, respectively, for Fn = 4000 μN. The values of μ were found to decrease with the increases in the Al compositions. We concluded that the Al composition played an important role in the reconstruction of the crystallites, which induced the transition phenomenon of brittleness to ductility in the AlxGa1−xN system. [ABSTRACT FROM AUTHOR]

Aluminium Gallium Nitride (AlyGa1-yN) quantum dots (QDs) with thin sub-µm AlxGa1-xN layers (with x > y) were grown by molecular beam epitaxy on 3 nm and 6 nm thick hexagonal boron nitride (h-BN) initially deposited on c-sapphire substrates. An AlN layer was grown on h-BN and the surface roughness was investigated by atomic force microscopy for different deposited thicknesses. It was shown that for thicker AlN layers (i.e., 200 nm), the surface roughness can be reduced and hence a better surface morphology is obtained. Next, AlyGa1-yN QDs embedded in Al0.7Ga0.3N cladding layers were grown on the AlN and investigated by atomic force microscopy. Furthermore, X-ray diffraction measurements were conducted to assess the crystalline quality of the AlGaN/AlN layers and examine the impact of h-BN on the subsequent layers. Next, the QDs emission properties were studied by photoluminescence and an emission in the deep ultra-violet, i.e., in the 275–280 nm range was obtained at room temperature. Finally, temperature-dependent photoluminescence was performed. A limited decrease in the emission intensity of the QDs with increasing temperatures was observed as a result of the three-dimensional confinement of carriers in the QDs. [ABSTRACT FROM AUTHOR]

The piezoelectric and spontaneous polarization of wurtzite ScxAl1−xN, GaxAl1−xN, and InxAl1−xN ternary compounds dramatically affects the electrical properties of pseudomorphic MexAl1−xN/GaN, MexAl1−xN/AlN, and MexAl1−xN/InN heterostructures and devices (Me: = Sc, Ga, In), due to bound interface charges caused by gradients in polarization at surfaces and heterointerfaces. We have calculated the piezoelectric and spontaneous polarization of undoped, metal polar ScxAl1−xN barrier layers (0 ≤ x ≤ 0.5) pseudomorphically grown on InN, GaN, and AlN buffer layers, in order to compare the polarization induced surface and interface charges determined to the ones predicted and measured in heterostructures with GaxAl1−xN and InxAl1−xN barriers (0 ≤ x ≤ 1.0). To facilitate the inclusion of the predicted polarization in future simulations, we give explicit prescriptions to calculate polarization induced bound interface charges for arbitrary x and barrier thicknesses up to 50 nm in each of the ternary III-N alloy heterostructures. In addition, we predict the electron sheet charges confined in heterostructures with positive polarization induced interface charges taking limitations for the epitaxial growth by strain and critical barrier thicknesses into account. Based on these results, we provide a detailed comparison of the sheet resistances and current-carrying capabilities of the heterostructures investigated, pointing to a superior potential of ScAlN/GaN based heterostructures for processing improved high electron mobility transistors for high-frequency and power electronic applications. [ABSTRACT FROM AUTHOR]

It has been previously shown that hole/donor traps at the (Al, Ga) N/GaN interface cause DC-RF dispersion and output conductance in N-polar GaN high electron mobility transistors (HEMTs). In this work, we systematically studied the impact of hole trap energy and density on two-dimensional electron gas (2DEG) density using Silvaco Atlas. Simulation results revealed that the exclusion of the hole traps in the model results in an underestimation of 2DEG density compared to experimentally obtained 2DEG density. By comparing simulations with the experimental results, a hole trap with a density of 3 × 1013 cm−2 at 280 meV above the valence band at the AlN/GaN negative polarization interface was estimated. Three different silicon doping schemes were then examined to suppress the effect of traps. Delta doping (15 nm) at the GaN buffer and barrier interface (doping Scheme-A) is effective in compensating traps present at that interface but insufficient to compensate traps near the GaN channel. Similarly, doping the back-barrier (doping scheme-B) is sufficient to neutralize traps in the middle of the back-barrier and close to the channel but inadequate to neutralize traps at the buffer–barrier interface. Series-C doping employs a combination of doping schemes A and B that effectively neutralizes traps present at all interfaces while simultaneously modulating the 2DEG charge density. An ultra-scaled 5-nm-thick GaN HEMT epitaxial structure was also designed by band engineering that can maintain high 2DEG density in the channel (2 × 013 cm−2) with less than 5% parasitic charge and trap ionization over a wide range of doping from 6 × 1018 cm−3 to 1 × 1019 cm−3. [ABSTRACT FROM AUTHOR]

Aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure devices have proven to be highly effective for high‐frequency power amplifiers and power switching applications with improved performance compared to those made with traditional silicon technology and other advanced semiconductor technologies. The development of enhancement‐mode (E‐mode) AlGaN/GaN high electron mobility transistors (HEMTs) and metal–insulator–semiconductor HEMTs (MIS‐HEMTs) has been a focus in recent years due to their potential applications. Arising from the concept of a flash‐memory‐like hybrid ferroelectric charge storage structure, the high‐performance hybrid ferroelectric charge storage gate (FEG) GaN HEMT has gradually gained a great deal of attention due to the concept being a useful and versatile tool to realize E‐mode operations. This article attempts to review the latest progresses in this technology, including alternative improvements and device characteristics. Future challenges for the E‐mode FEG‐HEMT are also discussed. [ABSTRACT FROM AUTHOR]

Leishmaniasis is considered as one of the 20 neglected tropical diseases. Current methods of leishmanial diagnosis depend on conventional laboratory‐based techniques, which are time‐consuming, costly and require special equipment and trained personnel. In this context, we aimed to provide an immuno field effect transistors (ImmunoFET) biosensor that matches the conventional standards for point‐of‐care (POC) monitoring and detection of Leishmania (L.) donovani/Leishmania major. Crude antigens prepared by repeated freeze thawing of L. donovani/L. major stationary phase promastigotes were used for ELISA and ImmunoFETs. Lesishmania‐specific antigens were serially diluted in 1× PBS from a concentration of 106–102 parasites/mL. A specific polyclonal antibody‐based sandwich ELISA was established for the detection of Leishmania antigens. An immunoFET technology‐based POC novel assay was constructed for the detection of Leishmania antigens. Interactions between antigen–antibody at the gate surface generate an electrical signal that can be measured by semiconductor field‐effect principles. Sensitivity was considered and measured as the change in current divided by the initial current. The final L. donovani/L. major crude antigen protein concentrations were measured as 1.50 mg/mL. Sandwich ELISA against the Leishmania 40S ribosomal protein detected Leishmania antigens could detect as few as 100 L. donovani/L. major parasites. An immunoFET biosensor was constructed based on the optimization of aluminium gallium nitride/gallium nitride (AlGaN/GaN) surface oxidation methods. The device surface was composed by an AlGaN/GaN wafer with a 23 nm AlGaN barrier layer, a 2 μm GaN layer on the silicon carbide (SiC) substrate for Leishmania binding, and coated with a specific antibody against the Leishmania 40S ribosomal protein, which was successfully detected at concentrations from 106 to 102 parasites/mL in 1× PBS. At the concentration of 104 parasites, the immunoFETs device sensitivities were 13% and 0.052% in the sub‐threshold regime and the saturation regime, respectively. Leishmania parasites were successfully detected by the ImmunoFET biosensor at a diluted concentration as low as 150 ng/mL. In this study, the developed ImmunoFET biosensor performed well. ImmunoFET biosensors can be used as an alternative diagnostic method to ELISA. Increasing the sensitivity and optimization of immuno‐FET biosensors might allow earlier and faster detection of leishmaniasis. [ABSTRACT FROM AUTHOR]

Herein, we report the design and implementation of planar and circular aluminium gallium nitride/Gallium nitride high electron mobility transistor (AlGaN/GaN HEMT) designs for pH sensing applications along with the insights into pH sensing to elucidate the underlying mechanism. The planar and circular devices were fabricated on the same wafer where the sensing membrane and passivation is realized by $\rm Al_{2}O_{3}$. The devices were encapsulated with photoresist and small openings are created for source/drain electrode contact pads and the sensing region where pH solution is confined to test the device response. The response of sensors is compared after normalizing circular HEMT output for a width of 100 $\mu{\rm m}$. The output current sensitivity is in the range of 75 (0.5 V) to 222.5 (2 V) $\mu {\rm A}$ /pH for planar HEMT device, whereas sensitivity values for circular HEMT is in the range of 0.152 (0.5 V) to 0.5 (2 V) mA/pH, respectively between pH 2 to 10. The circular HEMT device design depicted higher sensitivity and better linearity in response to pH due to the conduction throughout its circumference. The transient response is also studied and the results suggest a stable pH resolution and good linearity for both acidic and basic phosphate buffer saline (PBS). The higher current values are obtained, which is an advantage in terms of signal processing and conditioning unit for proper measurement that will help in reducing complexities in the integrated circuit (IC) and, therefore ease in point-of-care diagnosis. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated a low current collapse normally on Al2O3/AlGaN/GaN MIS-HEMT with in situ H-radical surface treatment on AlGaN. The in situ atomic pretreatment was performed in a specially designed chamber prior to the thermal ALD-Al2O3 deposition, which improved the Al2O3/AlGaN interface with D i t of ~2 × 1012 cm−2 eV−1, and thus effectively reduced the current collapse and the dynamic R o n degradation. The devices showed good electrical performance with low V t h hysteresis and peak trans-conductance of 107 mS/mm. Additionally, when the devices operated under 25 °C pulse-mode stress measurement with V D S , Q = 40 V (period of 1 ms, pulse width of 1 μ s), the dynamic R o n increase of ~14.1% was achieved. [ABSTRACT FROM AUTHOR]

Aluminum gallium nitride [(Al,Ga)N] has gained significant attention in recent years due to its potential for highly efficient light emitters operating in the deep ultra-violet (UV) range (<280 nm). However, given that current devices exhibit extremely low efficiencies, understanding the fundamental properties of (Al,Ga)N-based systems is of key importance. Here, using a multi-scale simulation framework, we study the impact of alloy disorder on carrier transport, radiative and non-radiative recombination processes in a c-plane Al0.7Ga0.3N/Al0.8Ga0.2N quantum well embedded in a p–n junction. Our calculations reveal that alloy fluctuations can open "percolative" pathways that promote transport for the electrons and holes into the quantum well region. Such an effect is neglected in conventional and widely used transport simulations. Moreover, we find that the resulting increased carrier density and alloy induced carrier localization effects significantly increase non-radiative Auger–Meitner recombination in comparison to the radiative process. Thus, to suppress such non-radiative process and potentially related material degradation, a careful design (wider well, multi-quantum wells) of the active region is required to improve the efficiency of deep UV light emitters. [ABSTRACT FROM AUTHOR]

The present work, theoretically examined the poliovirus sensor model composed of one-dimensional photonic crystal with defect. The transfer matrix method with the help of MATLAB software has been used to detect poliovirus present in the water sample. The main objective of the present work is to design an efficient sensor by identifying the minute variation in the refractive index of water sample due to change in the poliovirus concentration present in the sample. The alternate layers of aluminum nitride and gallium nitride has been taken to realize Bragg reflector having defect layer of air at center of the Bragg reflector. The effect of change in thickness of defect layer region, period number and incident angle corresponding to transverse electric wave has been examined to optimize the structure which correspond maximum performance of the proposed poliovirus sensing structure. The maximum performance of the structure has been obtained with optimum value of defect layer thickness 1200 nm, period number 10 and incident angle 40°. Under optimum condition maximum sensitivity of 1189.65517 nm/RIU has been obtained when the structure is loaded with waters sample of poliovirus concentration C = 0.005 g/ml whereas figure of merit, quality factor, signal to noise ratio, dynamic range, limit of detection and resolution values become 2618.28446 per RIU, 3102.06475, 2.27791, 2090.99500, 1.91E−05 and 0.24656 respectively. [ABSTRACT FROM AUTHOR]

This paper presents technology computer-aided design (TCAD) modeling of an enhancement-mode aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high electron mobility transistor (HEMT) with extensive π-gate optimization for high-power and radio frequency (RF) applications. Effects of the gate voltages on threshold (Vth), transconductance (gm), breakdown voltage (VBR), cutoff frequency (fT), maximum frequency of oscillation (fmax) and minimum noise figure (NFmin) are systematically investigated with different gate structures (π–Shaped p-GaN MISHEMT, π–Shaped p-GaN HEMT, π–Gate HEMT). A comparative study demonstrates that π–Gate with additional p-GaN and insulating layer makes the device effectively operate in the enhancement mode having a threshold voltage (Vth) = 1.72 V with a breakdown voltage (VBR) = 341 V, exhibiting better gate control with maximum transconductance (gm,max) of 0.321 S/mm. In addition, the proposed device architecture with an optimized gate structure maintains a balance between a positive device threshold and a high breakdown voltage and achieves a better noise immunity with the minimum noise figure of 0.64 dB while operating at 10 GHz with a cutoff frequency (fT) of 33.4 GHz, and a maximum stable operating frequency (fmax) of 82.3 GHz. Moreover, the device achieved an outstanding Vth, gm,max, VBR, fT, fmax and NFmin making it suitable for high-power, high-speed electronics, and low-noise amplifiers. [ABSTRACT FROM AUTHOR]

The application of deep ultraviolet detection (DUV) in military and civil fields has increasingly attracted the attention of researchers' attention. Compared with the disadvantages of organic materials, such as complex molecular structure and poor stability, inorganic materials are widely used in the field of DUV detection because of their good stability, controllable growth, and other characteristics. Rapid advances in preparing high-quality ultrawide-bandgap (UWBG) semiconductors have enabled the realization of various high-performance DUV photodetectors with different geometries, which provide an avenue for circumventing numerous disadvantages in traditional detectors. Herein, the development history and types of DUV detectors are briefly introduced. Typical UWBG detection materials and their preparation methods, as well as their research and application status in the field of DUV detection, are emphatically summarized and reviewed, including III-nitride semiconductors, gallium oxide, diamond, etc. Finally, problems pertaining to DUV detection materials, such as the growth of materials, the performance of devices, and their future development, are also discussed. [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth of high Al-content AlGaN often results in a high density of threading dislocations and surface hexagonal hillocks, which degrade the performance and reliability of AlGaN-based UVC light emitting diodes (LEDs). In this study, the degradation mechanism and impurity/defect behavior of UVC LEDs in relation to the hexagonal hillocks have been studied in detail. It was found that the early degradation of UVC LEDs is primarily caused by electron leakage. The prominent contribution of the hillock edges to the electron leakage is unambiguously evidenced by the transmission electron microscopy measurements, time-of-flight secondary ion mass spectrometry, and conductive atomic force microscopy. Dislocations bunching and segregation of impurities, including C, O, and Si, at the hillock edges are clearly observed, which facilitate the trap-assisted carrier tunneling in the multiple quantum wells and subsequent recombination in the p-AlGaN. This work sheds light on one possible degradation mechanism of AlGaN-based UVC LEDs. [ABSTRACT FROM AUTHOR]

Aluminum gallium nitride (AlGaN) nanowires by molecular beam epitaxy (MBE) have become an emerging platform for semiconductor deep ultraviolet (UV) light-emitting diodes (LEDs). Despite of the progress, much less attention has been paid to the effect of substrate rotation speed on the device performance. Herein, we investigate the effect of the substrate rotation speed on the nanowire height and diameter uniformity, as well as the electrical and optical performance of MBE-grown AlGaN nanowire deep UV LED structures with low and high substrate rotation speeds. It is found that by increasing the substrate rotation speed from 4 revolutions per minute (rpm) to 15 rpm, the statistical variation of the nanowire height and diameter is reduced significantly. Increasing the substrate rotation speed also improves the device electrical performance, with a factor of 4 reduction on the device series resistance. This improved electrical performance further transfers to the improved optical performance. The underlying mechanisms for these improvements are also discussed. [ABSTRACT FROM AUTHOR]

Surface-emitting (SE) semiconductor lasers have changed our everyday life in various ways such as communication and sensing. Expanding the operation wavelength of SE semiconductor lasers to shorter ultraviolet (UV) wavelength range further broadens the applications to disinfection, medical diagnostics, phototherapy, and so on. Nonetheless, realizing SE lasers in the UV range has remained to be a challenge. Despite of the recent breakthrough in UV SE lasers with aluminum gallium nitride (AlGaN), the electrically injected AlGaN nanowire UV lasers are based on random optical cavities, whereas AlGaN UV vertical-cavity SE lasers (VCSELs) are all through optical pumping and are all with large lasing threshold power densities in the range of several hundred kW/cm2 to MW/cm2. Herein, we report ultralow threshold, SE lasing in the UV spectral range with GaN-based epitaxial nanowire photonic crystals. Lasing at 367 nm is measured, with a threshold of only around 7 kW/cm2 (~ 49 μJ/cm2), a factor of 100× reduction compared to the previously reported conventional AlGaN UV VCSELs at similar lasing wavelengths. This is also the first achievement of nanowire photonic crystal SE lasers in the UV range. Further given the excellent electrical doping that has already been established in III-nitride nanowires, this work offers a viable path for the development of the long-sought-after semiconductor UV SE lasers. [ABSTRACT FROM AUTHOR]

Aluminum gallium nitride (AlGaN) is a nanohybrid semiconductor material with a wide bandgap, high electron mobility, and high thermal stability for various applications including high-power electronics and deep ultraviolet light-emitting diodes. The quality of thin films greatly affects their performance in applications in electronics and optoelectronics, whereas optimizing the growth conditions for high quality is a great challenge. Herein, we have investigated the process parameters for the growth of AlGaN thin films via molecular dynamics simulations. The effects of annealing temperature, the heating and cooling rate, the number of annealing rounds, and high temperature relaxation on the quality of AlGaN thin films have been examined for two annealing modes: constant temperature annealing and laser thermal annealing. Our results reveal that for the mode of constant temperature annealing, the optimum annealing temperature is much higher than the growth temperature in annealing at the picosecond time scale. The lower heating and cooling rates and multiple-round annealing contribute to the increase in the crystallization of the films. For the mode of laser thermal annealing, similar effects have been observed, except that the bonding process is earlier than the potential energy reduction. The optimum AlGaN thin film is achieved at a thermal annealing temperature of 4600 K and six rounds of annealing. Our atomistic investigation provides atomistic insights and fundamental understanding of the annealing process, which could be beneficial for the growth of AlGaN thin films and their broad applications. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition of indium nitride (InN) is severely limited by the low thermal stability of the material, and, thus, low-temperature deposition processes such as atomic layer deposition (ALD) are needed to deposit InN films. The two chemically and structurally closely related materials—aluminum nitride and gallium nitride (GaN)—can be deposited by both plasma and thermal ALD, with ammonia (NH3) as a nitrogen precursor in thermal processes. InN, however, can only be deposited using plasma ALD, indicating that there might be a limitation to thermal ALD with NH3 for InN. We use quantum-chemical density functional theory calculations to compare the adsorption process of NH3 on GaN and InN to investigate if differences in the process could account for the lack of thermal ALD of InN. Our findings show a similar reactive adsorption mechanism on both materials, in which NH3 could adsorb onto a vacant site left by a desorbing methyl group from the surfaces. The difference in energy barrier for this adsorption indicates that the process is many magnitudes slower on InN compared to GaN. Slow kinetics would hinder NH3 from reactively adsorbing onto InN in the timeframe of the ALD growth process and, thus, limit the availability of a thermal ALD process. [ABSTRACT FROM AUTHOR]

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) “fabricated to improve device radio frequency (RF) performance for Ka-band applications” are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load–pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications.

The current research investigates the potential advantages of replacing Al2O3 with (Ta2O5)0.12(Al2O3)0.88 as a higher dielectric constant (κ) gate dielectric for GaN-based metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs). The electrical characteristics of GaN-capped AlGaN/GaN MOS-HEMT devices with (Ta2O5)0.12(Al2O3)0.88 as the gate dielectric are compared to devices with Al2O3 gate dielectric and devices without any gate dielectric (Schottky HEMTs). Compared to the Al2O3 MOS-HEMT, the (Ta2O5)0.12(Al2O3)0.88 MOS-HEMT achieves a larger capacitance and a smaller absolute threshold voltage, together with a higher two-dimensional electron gas carrier concentration. This results in a superior improvement of the output characteristics with respect to the Schottky HEMT, with higher maximum and saturation drain current values observed from DC current-voltage measurements. Gate transfer measurements also show a higher transconductance for the (Ta2O5)0.12(Al2O3)0.88 MOS-HEMT. Furthermore, from OFF-state measurements, the (Ta2O5)0.12(Al2O3)0.88 MOS-HEMT shows a larger reduction of the gate leakage current in comparison to the Al2O3 MOS-HEMT. These results demonstrate that the increase in κ of (Ta2O5)0.12(Al2O3)0.88 compared with Al2O3 leads to enhanced device performance when the ternary phase is used as a gate dielectric in the GaN-based MOS-HEMT. [ABSTRACT FROM AUTHOR]

We report on the results of a comprehensive study of THz emission from a set of dedicated AlGaN/GaN high-electron-mobility transistors. We find that voltage-biased transistors indeed emit in the THz frequency range, as reported in the literature; however, our data let us conclude that this radiation cannot be directly attributed to plasmonic instability phenomena. Instead, two other distinct mechanisms are identified. One is based on high-frequency self-oscillations originating from positive feedback within the frequency range where the transistor provides gain. Such oscillations are especially facilitated by the integration of antenna structures and cease to exist after taking specific measures for circuit stabilization. Another mechanism is identified for the case of broadband emission from multifinger transistors fabricated without any specific antenna. In contrast to the predictions of the plasmonic instability picture, the spectra of this emission depend on the gate and drain biasing conditions and on the bias modulation frequency. This emission can be understood as a combination of thermal emission from the heated material and from thermally excited plasmons and trap states. [ABSTRACT FROM AUTHOR]

In this work, an AlGaN/GaN-HEMT heterostructure is exemplarily studied by a strict place-to-place correlational approach in order to help clarify some open questions in the wide field of reliability topics. Especially, vertical leakage current, its relation to dislocations in general, and specific types in particular are investigated on a highly defective material. With the aid of atomic force microscopy (AFM) in tapping mode, cathodoluminescence imaging, defect selective etching, and energy dispersive X-ray, the material's defect content around the device relevant two dimensional electron gas is analyzed. The total dislocation density, as well as the density of threading screw, edge, and mixed type dislocations, is systematically investigated directly. The obtained result is statistically much more significant than is possible by conventional transmission electron microscopy studies and more precise than the results obtained by the indirect method of rocking curve analysis. The method of conductive AFM allowed mapping of variations in the vertical leakage current, which could be correlated with variations in barrier leakage or gate leakage. Spots of locally high leakage current could be observed and directly assigned to dislocations with a screw component, but with significant differences even within the same group of dislocation types. The electrical activity of dislocations is discussed in general, and a fundamental model for a potential dislocation driven vertical leakage is proposed. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the On/Off switching mechanism of AlGaN/GaN Fin-high-electron-mobility transistors (Fin-HEMTs) comprehensively through experiment and simulation. The "tri-gated fin channel" is characterized by a direct gate-metal/semiconductor contact, that is, a Schottky gate instead of a conventional metal-insulator-semiconductor gate stack. The minimum fin width of our Fin-HEMT is 100 nm with a threshold voltage (Vth) of −0.65 V, and a positive Vth shift with a channel width scaling is also obtained in the experiment. Through the 3-D simulation, it can be found that while the channel width is narrow enough, the carrier in the fin channel is dominated by the side-gate laterally instead of the vertical top-gate control. The band diagram also indicates that the conduction band in the fin channel is pulled up more rapidly than the planar HEMT with a negative gate bias. This result can be attributed to channel pinch-off through the depletion region which is created by the Schottky side-gate. Therefore, a narrow fin channel can lead to the "early pinch-off effect" compared with the planar HEMT. [ABSTRACT FROM AUTHOR]

This work investigated the effects of single stress and electro-thermo-mechanical coupling stress on the electrical properties of top-cooled enhancement mode (E-mode) Aluminium Gallium Nitride/Gallium Nitride (AlGaN/GaN) high electron mobility transistor (HEMT) (GS66508T). Planar pressure, linear deformation, punctate deformation, environmental temperature, electro-thermal coupling, thermo-mechanical coupling, and electro-thermo-mechanical coupling stresses were applied to the device. It was found that different kinds of stress had different influence mechanisms on the device. Namely, excessive mechanical pressure/deformation stress caused serious, irrecoverable degradation of the device's leakage current, with the gate leakage current (Ig) increasing by ~107 times and the drain-to-source leakage current (Idss) increasing by ~106 times after mechanical punctate deformation of 0.5 mm. The device characteristics were not restored after the mechanical stress was removed. Compared with three mechanical stresses, environmental thermal stress had a greater influence on the device's transfer characteristic and on-resistance (Ron) but far less influence on Ig and Idss. As was expected, multiple stress coupled to the device promoted invalidation of the device. For more in-depth investigation, finite element simulation carried out with COMSOL was used to analyze the effect of electro-thermo-mechanical coupling stress on top-cooled E-mode AlGaN/GaN HEMT. The results of the experiments and simulation demonstrated that single and coupled stresses, especially mechanical stress coupled with other stresses, degraded the electrical properties or even caused irreversible damage to top-cooled E-mode AlGaN/GaN HEMT. Mechanical stress should be reduced as much as possible in the packaging design, transportation, storage, and application of top-cooled E-mode AlGaN/GaN HEMT. [ABSTRACT FROM AUTHOR]

The effects of pre-metallization of the growth surface on film stress and structural properties of undoped and Ge-doped AlxGa1−xN (x ~ 0.5–0.6) epilayers grown by metal–organic chemical vapor deposition (MOCVD) on 500 nm-thick hydride vapor-phase epitaxy (HVPE) AlN/sapphire templates were investigated. AlxGa1−xN typically grows under compressive stress on the AlN templates due to its larger lattice parameter, which can lead to increased surface roughness and V-pits in undoped and Ge-doped AlxGa1−xN. The introduction of the group III sources in the growth ambient for a short period of time (5 s) prior to the addition of NH3 induced a tensile growth stress in the AlxGa1−xN, as measured by in situ wafer curvature measurements, which correlated with an improvement in the surface morphology. However, the pre-metallization was also observed to result in the deposition of a carbon-rich layer at the AlxGa1−xN/AlN interface and an increased density of screw-type dislocations as measured by post-growth x-ray diffraction. By utilizing a pre-metallization step with a lower AlxGa1−xN growth rate, it was possible to eliminate the carbon interfacial layer and maintain low surface v-pitting and threading dislocation density in Ge-doped AlxGa1−xN. The results provide insight into the impact of pre-metallization on the AlxGa1−xN/AlN interface and the structural properties of the layers. [ABSTRACT FROM AUTHOR]

Heteroepitaxial crystallographic tilt has been investigated as a possible strain‐relief mechanism in Al‐rich (Al>50%) AlGaN heteroepitaxial layers grown on single‐crystal (0001) AlN substrates with varying miscuts from 0.05° to 4.30°. The magnitude of the elastic lattice deformation‐induced tilt increases monotonically with the miscut angle, tightly following the Nagai tilt model. Although tilt angles as high as 0.1° are recorded, reciprocal space mapping (RSM) broadening and wafer bow measurements do not show any significant changes as a function of the heteroepitaxial tilt angle. While crystallographic tilting has been shown to be effective in controlling strain in some other heteroepitaxial systems, it does not provide any appreciable strain relief of the compressive strain in AlGaN/AlN heteroepitaxy. [ABSTRACT FROM AUTHOR]

This letter analyzes the velocity-field relationship of AlGaN/GaN HFETs via Monte Carlo simulation. This method is based on complete scattering mechanisms such as polarized coulomb field scattering (PCF scattering), polar optical phonon scattering, acoustic deformation potential scattering, inter-valley phonon scattering, and piezoelectric scattering. It is found that the gate bias voltage affects the PCF scattering intensity and the PCF scattering intensity influences the drift velocity under a high electric field. A decrease in peak steady-state drift velocity is observed for our fabricated AlGaN/GaN HFETs from ${1.335}\times {10}^{{5}}$ m/s at $\text{V}_{\text {gs}} =$ 0 V to ${1.23}\times {10}^{{5}}$ m/s at $\text{V}_{\text {gs}} =-3$ V as the gate voltage becomes more negative. When combined with the velocity-field relationship obtained from Monte Carlo simulations, the calculated current-voltage characteristics of AlGaN/GaN HFET devices are in good agreement with our experiment results. The electron saturation drift velocity deviation of AlGaN/GaN HFETs from the Monte Carlo simulation of the GaN material is attributed to the presence of PCF scattering in AlGaN/GaN HFETs. In the study, we provide strong support for the accurate modeling of AlGaN/GaN HFETs. [ABSTRACT FROM AUTHOR]