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The radio frequency (RF) degradation mechanism under high temperature is proposed in this paper. The saturated output power (P sat), power added efficiency (PAE) and gain of the HEMTs deteriorate significantly under high power dissipation operation conditions, which contribute to an elevation of the junction temperature (T j). The high T j causes a negative shift of the threshold voltage and a reduction of electron mobility, as well as enhancing the trapping effects of the devices. As a result, the P sat and PAE of the high-power HEMTs (P sat = 152 W) decreased by 0.76 dB and 8.3%, respectively, which is more severe compared to low-power HEMTs (P sat = 20 W), where P sat and PAE reduced by 0.16 dB and 3.1% when the operation temperature was increased from 25 °C to 150 °C. By increasing the gate-to-drain distance from 1.625 to 2.175 μ m, drain current stability and high temperature reverse bias reliability are improved. The results demonstrate that the trapping effect can be suppressed by decreasing the electric field under the gate; therefore, the RF output characteristics are boosted by 1.2 W, 1 dB and 2.6% for a device with gate width of 11.52 mm. [ABSTRACT FROM AUTHOR]

Due to the suitable bandgap structure, efficient conversion rates of photon to electron, adjustable optical bandgap, high electron mobility/aspect ratio, low defects, and outstanding optical and electrical properties for device design, III–V semiconductors have shown excellent properties for optoelectronic applications, including photodiodes, photodetectors, solar cells, photocatalysis, etc. In particular, III–V nanostructures have attracted considerable interest as a promising photodetector platform, where high-performance photodetectors can be achieved based on the geometry-related light absorption and carrier transport properties of III–V materials. However, the detection ranges from Ultraviolet to Terahertz including broadband photodetectors of III–V semiconductors still have not been more broadly development despite significant efforts to obtain the high performance of III–V semiconductors. Therefore, the recent development of III–V photodetectors in a broad detection range from Ultraviolet to Terahertz, and future requirements are highly desired. In this review, the recent development of photodetectors based on III–V semiconductor with different detection range is discussed. First, the bandgap of III–V materials and synthesis methods of III–V nanostructures are explored, subsequently, the detection mechanism and key figures-of-merit for the photodetectors are introduced, and then the device performance and emerging applications of photodetectors are provided. Lastly, the challenges and future research directions of III–V materials for photodetectors are presented. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is a promising wide bandgap semiconductor that is viewed as a contender for the next generation of high-power electronics due to its high theoretical breakdown electric field and large Baliga's figure of merit. Here, we report a facile route of synthesizing β -Ga2O3 via direct oxidation conversion using solution-processed two-dimensional (2D) GaS semiconducting nanomaterial. Higher order of crystallinity in x-ray diffraction patterns and full surface coverage formation in scanning electron microscopy images after annealing were achieved. A direct and wide bandgap of 5 eV was calculated, and the synthesized β -Ga2O3 was fabricated as thin film transistors (TFT). The β -Ga2O3 TFT fabricated exhibits remarkable electron mobility (1.28 cm2 Vs−1) and a good current ratio (I on/ I off) of 2.06 × 105. To further boost the electrical performance and solve the structural imperfections resulting from the exfoliation process of the 2D nanoflakes, we also introduced and doped graphene in β -Ga2O3 TFT devices, increasing the electrical device mobility by ∼8-fold and thereby promoting percolation pathways for the charge transport. We found that electron mobility and conductivity increase directly with the graphene doping concentration. From these results, it can be proved that the β -Ga2O3 networks have excellent carrier transport properties. The facile and convenient synthesis method successfully developed in this paper makes an outstanding contribution to applying 2D oxide materials in different and emerging optoelectronic applications. [ABSTRACT FROM AUTHOR]

Highly oriented, single crystalline, quaternary alloy chalcogenide crystal, Mo x W1− x S2 y Se2(1− y), is synthesized using a high temperature chemical vapor transport technique and its transport properties studied over a wide temperature range. Field effect transistors (FET) with bottom gated configuration are fabricated using Mo0.5W0.5SSe flakes of different thicknesses, from a single layer to bulk. The FET characteristics are thickness tunable, with thin flakes (1–4 layers) exhibiting n-type transport behaviour while ambipolar transfer characteristics are observed for thicker flakes (>90 layers). Ambipolar behavior with the dominance of n-type over p-type transport is noted for devices fabricated with layers between 9 and 90. The devices with flake thickness ∼9 layers exhibit a maximum electron mobility 63 ± 4 cm2 V−1s−1 and an I ON/ I OFF ratio >108. A maximum hole mobility 10.3 ± 0.4 cm2 V−1s−1 is observed for the devices with flake thickness ∼94 layers with I ON/ I OFF ratio >102–103 observed for the hole conduction. A maximum I ON/ I OFF for hole conduction, 104 is obtained for the devices fabricated with flakes of thickness ∼7–19 layers. The electron Schottky barrier height values are determined to be ∼23.3 meV and ∼74 meV for 2 layer and 94 layers flakes respectively, as measured using low temperature measurements. This indicates that an increase in hole current with thickness is likely to be due to lowering of the band gap as a function of thickness. Furthermore, the contact resistance (R ct) is evaluated using transmission line model (TLM) and is found to be 14 kohm. μ m. These results suggest that quaternary alloys of Mo0.5W0.5SSe are potential candidates for various electronic/optoelectronic devices where properties and performance can be tuned within a single composition. [ABSTRACT FROM AUTHOR]

The recombination dynamics are studied in viscous electron–hole plasma, consisting of electrons and photo-generated heavy and light holes, formed in the high-mobility mesoscopic GaAs channel. It is shown that an increase in the pump power reduces the concentration and mobility of background electrons, which, in turn, slows down their recombination with photogenerated holes. At a critical pump power, the recombination time begins to decrease, which is a consequence of the transition of a viscous electron–hole plasma from the hydrodynamic regime to the Drude diffusive regime. The observed transition occurs when the scattering of electrons with disorder begins to dominate over electron–electron scattering, which leads to the transformation of an inhomogeneous Poiseuille charge flow into a homogeneous diffusion flow. As a result, an optical analogue of the Gurzhi effect has been found. [ABSTRACT FROM AUTHOR]

This work is motivated by the recent fabrication of a new four-atom-thick hexagonal polymorph from group IV monochalcogenide, so-called γ -GeSe (Lee et al 2021 Nano Lett. 21 4305). In this paper, we propose and examine the structural characteristics, electronic properties, and carrier mobility of monolayers Janus γ -Ge2 XY ( X / Y = S, Se, or Te) based on comprehensive first-principles calculations. Monolayers γ -Ge2 XY are confirmed to be structurally stable. Our calculations reveal that γ -Ge2 XY monolayers are indirect semiconductors with Mexican-hat-like dispersions in the top valence band. While the effect of the electric field on the energy band dispersions of γ -Ge2 XY monolayers is weak, the energy band dispersions are changed drastically in the presence of strain, especially compressive strain. Interestingly, a structural phase transition from semiconductor to metal is observed in γ -Ge2 XY under compressive strain. γ -Ge2STe and γ -Ge2SeTe possess high electron mobility with values of 3.22 × 10 3 and 8.33 × 10 3 cm2 V−1 s−1, respectively. Our findings not only explore the fundamental physical properties of γ -Ge2 XY but also open up new opportunities in the design of high-performance electronic nanodevices based on layered nanomaterials with Mexican-hat-like dispersions. [ABSTRACT FROM AUTHOR]

Atomically thin transition metal dichalcogenides (TMDs), like MoS2 with high carrier mobilities and tunable electron dispersions, are unique active material candidates for next generation opto-electronic devices. Previous studies on ion irradiation show great potential applications when applied to two-dimensional (2D) materials, yet have been limited to micron size exfoliated flakes or smaller. To demonstrate the scalability of this method for industrial applications, we report the application of relatively low power (50 keV) 4He+ ion irradiation towards tuning the optoelectronic properties of an epitaxially grown continuous film of MoS2 at the wafer scale, and demonstrate that precise manipulation of atomistic defects can be achieved in TMD films using ion implanters. The effect of 4He+ ion fluence on the PL and Raman signatures of the irradiated film provides new insights into the type and concentration of defects formed in the MoS2 lattice, which are quantified through ion beam analysis. PL and Raman spectroscopy indicate that point defects are generated without causing disruption to the underlying lattice structure of the 2D films and hence, this technique can prove to be an effective way to achieve defect-mediated control over the opto-electronic properties of MoS2 and other 2D materials. [ABSTRACT FROM AUTHOR]

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work. [ABSTRACT FROM AUTHOR]

Polymer-assisted wet transfer of chemical vapor deposited (CVD) graphene has achieved great success towards the true potential for large-scale electronic applications, while the lack of an efficient polymer removal method has been regarded as a crucial factor for realizing high carrier mobility in graphene devices. Hereby, we report an efficient and facile method to clean polymer residues on graphene surface by merely employing solvent mixture of isopropanol (IPA) and water (H2O). Raman spectroscopy shows an intact crystal structure of graphene after treatment, and the x-ray photoelectron spectroscopy indicates a significant decrease in the Câ€"O and C=O bond signals, which is mainly attributed to the removal of polymer residues and further confirmed by subsequent atomic force microscopy analysis. More importantly, our gated measurements demonstrate that the proposed approach has resulted in a 3-fold increase of the carrier mobility in CVD graphene with the electron mobility close to 10 000 cm2 Vâˆ'1 Sâˆ'1, corresponding to an electron mean free path beyond 100 nm. This intrigues the promising application for this novel method in achieving ballistic transport for CVD graphene devices. [ABSTRACT FROM AUTHOR]

Taking into account the novel layered structure and unusual electronic properties of MoS2 and WS2 on the side the lack of dangling bonds between these two components and donorâ€"acceptor linkage effects, growth of the MoS2/WS2 vertical heterojunction film on the amorphous SiO2/Si substrate have created high demand. In this study, we reported the continuous, scalable, and vertical MoS2/WS2 heterostructure film by using a sputtering without a transfer step. The WS2 film was continuously grown on MoS2 and eventually led to the formation of the MoS2/WS2 vertical heterojunction film. Dozens of FETs fabricated on MoS2/WS2 continuous heterojunction film were created on the same substrate in a single lithographic fabrication step, allowing them to be commercialized and not only used in research applications. RAMAN spectra proved the formation of the MoS2/WS2 heterostructure film. In XPS measurements, it was shown that a separate MoS2 and WS2 layer was grown instead of the alloy structure. The polarity behavior of the MoS2/WS2 heterostructure FET was found to be modulated with different drain voltages as p-type to ambipolar and finally n-type conductivity because of the transition of band structure and Schottky barrier heights at different drain voltages. Electron mobility (7.2 cm2 V.sâˆ'1) and on/off ratio (104â€"105) exhibited by the MoS2/WS2 heterostructure FETs displayed a more improved electrical performance than that of individual WS2, MoS2 devices. It was observed that the mobility value of MoS2/WS2 FET was approximately 514 times greater than WS2 FET and 800 times greater than MoS2 FET. Additionally, the MoS2/WS2 FET on/off ratio was larger than 2 order MoS2 FET and 1 order WS2 FET. The film of continuous vertical heterojunctions as in the MoS2/WS2 currents in the study would be a promising candidate for nanoelectronics fields. This work demonstrated the progress towards realizing carrier-type controlled high-performance MoS2/WS2 heterojunction-based FETs for future logic devices. [ABSTRACT FROM AUTHOR]

In this paper, we systematically investigated the static properties and gate current mechanism of low-pressure chemical vapor deposition-SiN x /AlGaN/GaN metalâ€"insulatorâ€"semiconductor-high-electronmobility-transistor (MIS-HEMTs) at cryogenic temperature range from 10 K to 300 K. It is found that the threshold voltage of the device shows a positive shift due to the decreased carrier concentration at low temperature, and both the maximum transconductance and ON-resistance are improved at the low temperatures because of the enhanced electron mobility. Under very low electric field, the gate leakage exhibits ohmic conduction. With increasing forward gate bias, the dominant gate leakage mechanism at temperature below150 K gradually transits into trap-assisted tunneling, participating with a deep trap energy level of 0.73 eV in the SiN x dielectric, to Fowlerâ€"Nordheim (FN) tunneling. In contrast, the dominant gate leakage mechanism at temperature above 150 K transits from Pooleâ€"Frenkel emission, showing a low trap barrier height of 56 meV in the SiN x dielectric, to Fowlerâ€"FN tunneling with increasing forward gate bias. Under high reverse gate bias, carrier-limited gate current becomes the dominated gate leakage mechanism. [ABSTRACT FROM AUTHOR]

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq3/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq3) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 Ω/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10â€"6 cm2 Vâˆ'1 sâˆ'1 at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Coleâ€"Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes. [ABSTRACT FROM AUTHOR]

Charge transport behavior in SnO2 nanoparticle (NP) films is rather crucial to the optoelectronic devices. Temperature-dependent electrical results show that the electron transport in SnO2 NP films is dominated by the Mott variable-range hopping processes, i.e. the electrons are transported between different NPs through surface states rather than the conduction band of the nanocrystals, which is identical to the commonly used ZnO NP solids. Compared with ZnO, SnO2 films exhibit similar electron mobility but lower density of states (DOS). Therefore, we deduce that the low DOS in the SnO2 NP films should be the key factor limiting the device performance in compared with the ZnO as reported in most of the quantum-dot light-emitting diodes (QLEDs). Our work sheds light on optimizing SnO2 NP films for QLEDs. Moreover, we believe that the SnO2 remains a desirable candidate as the electron transport material for the QLEDs due to its excellent physicochemical stability. [ABSTRACT FROM AUTHOR]

A gated Hall-bar device is made from an epitaxially grown, free-standing InSb nanosheet on a hexagonal boron nitride (hBN) dielectric/graphite gate structure and the electron transport properties in the InSb nanosheet are studied by gate-transfer characteristic and magnetotransport measurements at low temperatures. The measurements show that the carriers in the InSb nanosheet are of electrons and the carrier density in the nanosheet can be highly efficiently tuned by the graphite gate. The mobility of the electrons in the InSb nanosheet is extracted from low-field magneotransport measurements and a value of the mobility exceeding ∼ 1.8 Ă— 104 cm2â‹...Vâˆ'1â‹...sâˆ'1 is found. High-field magentotransport measurements show well-defined Shubnikovâ€"de Haas (SdH) oscillations in the longitudinal resistance of the InSb nanosheet. Temperature-dependent measurements of the SdH oscillations are carried out and key transport parameters, including the electron effective mass m * ∼ 0.028 m 0 and the quantum lifetime Ď„ ∼ 0.046 ps, in the InSb nanosheet are extracted. It is for the first time that such experimental measurements have been reported for a free-standing InSb nanosheet and the results obtained indicate that InSb nanosheet/hBN/graphite gate structures can be used to develop advanced quantum devices for novel physics studies and for quantum technology applications. [ABSTRACT FROM AUTHOR]

The risk of pharmaceutical contamination is a growing ecological issue that affects every region of the globe. Continuous enhancement in the intake and negligent domestic ejection of these cytostatic agents are the main grounds for the occurrence of active residual metabolites in various aquatic environments. Electrochemical sensors are a capable substitute for other conventional analytical methods for monitoring toxic drug pollutants due to their beneficial features. Thus, the purpose of this work is to demonstrate an energy-efficient fabrication of neodymium vanadate integrated with boron-doped carbon (NdVO4/B–C) hybrid composite for the selective electrochemical determination of nilutamide (NT– anti-androgen drug). The choice of neodymium among rare earth metals has a significant impact on the electrochemical redox processes. In addition, rapid electron mobility for well-separated peaks and defined current potentials implies an improved active surface area in NdVO4. Therefore, the incorporation of B–C displays substantial enhancement in electronic conductivity, identifying the nanocomposite as a remarkable detecting candidate. The presence of multiple oxidation states of rare earth vanadate embedded on boron-doped activated carbon results in high synergistic interactions and advanced matrix structures that facilitate superlative electrocatalytic characteristics including the minimal Rct value (81.32 Ω.cm² ), wide linear-range responses (0.001–344 μM), low limit of detection (0.0002 μM), high sensitivity (5.56 μA·μM−1 ·cm−2 ), good stabilities (operational stability = 3000 s and storage stability = 20 days), and excellent selectivity (with an excess concentration of 12 interfering compounds). It is noteworthy that the NdVO4/B–C modified electrode provides an outstanding recovery range (±99.91%–99.94%) for real sample analysis, thus marking it to be a competitive sensor option for commercial usage. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gas (2DEG) with high electron mobility is highly desired to study the emergent properties and to enhance future device performance. Here we report the formation of 2DEG with high mobility at the interface between rock-salt BaO and perovskite SrTiO3. The interface consists of the ionically compensated BaO1 â€" δ layer and the electronically compensated TiO2 layer, which is demonstrated as a perfect interface without lattice mismatch. The so-formed interface features metallic conductivity with ultralow square resistance of 7.3 Ă— 10âˆ'4 Ω/â—» at 2 K and high residual resistance ratios R 300 K/ R 2 K up to 4200. The electron mobility reaches 69000 cm2â‹...Vâˆ'1â‹...sâˆ'1 at 2 K, leading to Shubnikovâ€"de Haas oscillations of resistance. Density functional theory calculations reveal that the effective charge transfers from BaO to the Ti 3 dxy orbital occur at the interface, leading to the conducting TiO2 layer. Our work unravels that BaO can adapt itself by removing oxygen to minimize the lattice mismatch and to provide substantial carriers to SrTiO3, which is the key to forming 2DEGs with high mobility at the interfaces. [ABSTRACT FROM AUTHOR]

Vanadium selenide (V2Se9) is a true one-dimensional (1D) crystal composed of atomic nanochains bonded by van der Waals (vdW) interactions. Recent experiments revealed the mechanical exfoliation of newly synthesized V2Se9. In this study, we predicted the electronic and transport properties of V2Se9 through computational analyses. We calculated the intrinsic carrier mobility of V2Se9 monolayers (MLs) and nanoribbons (NRs) using density functional theory and deformation potential theory. We found that the electron mobility of the two-dimensional (2D) (010)-plane ML of V2Se9 is highly anisotropic, reaching ÎĽ 2 D , z e = 1327 cm2 Vâˆ'1 sâˆ'1 across the chain direction. The electron mobility of 1D NR systems in a (010)-plane ML of V2Se9 along the chain direction continuously increased as the thickness increased from 1-chain to 4-chain NR (width below 3 nm). Interestingly, the electron mobility of 1D 4-chain NR along the chain direction ( ÎĽ 1 D , x e = 775 cm2 Vâˆ'1 sâˆ'1) was higher than that of a 2D (010)-plane ML ( ÎĽ 2 D , x e = 567 cm2 Vâˆ'1 sâˆ'1). These results demonstrate the potential of vdW-1D crystal V2Se9 as a new nanomaterial for ultranarrow (sub-3 nm width) optoelectronic devices with high electron mobility. [ABSTRACT FROM AUTHOR]

Atomically two-dimensional materials with direct band-gap and high carrier mobility are highly desirable due to their promising applications in electronic devices. Here, on the basis of ab initio calculations and global particle-swarm optimization method, we predict the B2S3 monolayer as a new semiconductor with favorable functional properties. The B2S3 monolayer possesses a high electron mobility of 553 cm2 V−1 s−1 and a direct band-gap of 1.85 eV. The direct band-gap can be manipulated under biaxial strain. Furthermore, B2S3 monolayer can absorb sunlight efficiently in the entire range of the visible light spectrum. Besides, this monolayer holds good dynamical, thermal, and mechanical stabilities. All the desired properties render B2S3 monolayer a promising candidate for future applications in high-speed (opto)electronic devices. [ABSTRACT FROM AUTHOR]

Recently, Nb3O7F (NOF) semiconductor has been intensively studied owing to its excellent ultraviolet activity, good thermal stability and low carrier recombination. In this work, we report a five-step technique to synthesize hollow carbon spheres (HCSs)/NOF hybrids. Activating the surface of HCSs by creating oxyfluorinated functionalization can easily trigger an interaction between oxyfluorinated HCSs and NOF intermediates, finally resulting in the formation of HCSs/NOF hybrids. By manipulating the contents of HCSs with unexceptionable electron mobility, the hybrids can simultaneously achieve narrower band gap, stronger light absorption and rapider charge transfer. As a consequence, HCSs/NOF hybrids exhibit enhanced photodegradation performance towards RhB solutions under simulated sunlight irradiation. Specially, HCSs/NOF-1.0 catalysts with 95.7% degradation efficiency within 40 min demonstrate approximately four times higher photocatalytic activity than that of pure NOF catalysts. The results may offer new inspirations for a design of novel catalysts with higher photoactivity. [ABSTRACT FROM AUTHOR]

In this study, we deposited Cu2ZnSnS4 (CZTS) thin films with various thicknesses using electrodeposition and sputtering methods to exploit them as counter electrodes (CEs) in Zn2SnO4 -based dye-sensitized solar cells (DSSCs). The ternary Zn2SnO4 compound with wide bandgap energy, large corrosive resistivity, high electron mobility, and an appropriate conduction band edge position concerning the dye molecules (N719) can be an outstanding alternative for photoanode besides CZTS CE in DSSCs. On the other hand, CZTS is an impressive candidate as a CE material, but its electrocatalytic activity for the recovery of ionic species can be different depending on the synthesis process. Our results indicated the creation of porous morphology in the solution-based deposited films, which yields higher electrocatalytic activity in the CE performance in comparison with the physical deposition method, resulting in short circuit current densities of 9.77 and 8.40 mA cm−2 and open-circuit voltages of 633 and 583 mV for the DSSCs prepared by the respective techniques. The large active area and highly crystallized CZTS films, prepared by the electrodeposition method, led to an around 50% efficiency improvement compared to the widely used, more expensive platinum. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting has been studied extensively as an environmentally friendly technology for hydrogen production using solar energy. WO3 is considered a promising semiconducting material for photoanodes due to its high electron mobility, good hole diffusion length, and chemical stability. Periodic nanostructures of WO3 have been investigated for enhancing the PEC performance of WO3-based photoanodes. In this study, facile fabrication of periodic nanostructures of WO3 was achieved using reverse nanoimprint lithography, and the multilayer stacking of nanopatterned WO3 film was also confirmed. The multilayer nanopatterned WO3 films were used as photoanodes for PEC water splitting. The performance of the fabricated photoanode in PEC was 2 times higher than that of planar WO3 film due to its higher light absorbance and lower charge transfer resistance. [ABSTRACT FROM AUTHOR]

Perovskite-based van der Waals heterostructures with high carrier mobility and perfect photoresponse performance can be used to design transistors and photovoltaic devices. However, the function of a single heterojunction is relatively limited because of its specific energy band type. To achieve more controllable device functions, in this work, the band structure, effective mass, optical absorption spectrum, differential charge density and other electronic and optical properties for the novel heterostructure system composed of emerging two-dimensional material Pd2Se3 with a high electron mobility and all-inorganic halide perovskite Cs2PbI2(1+x)Cl2(1−x) is systematically studied by using density functional theory. The results demonstrate that the band alignments in Cs2PbI2Cl2/Pd2Se3 heterostructure realize the transition from type-I to type-II by changing the concentration of I and Cl atoms in the all-inorganic two-dimensional Ruddlesen-Popper perovskite Cs2PbI2Cl2, which can be applied to different functional devices. With the increase of iodine atoms, the valence band maximum (VBM) contributed by Pd2Se3 in the heterostructure moves downward, and the valence band of Cs2PbI2Cl2 becomes the new VBM. Moreover, the transport and optical properties for the Cs2PbI2Cl2/Pd2Se3 heterostructure can be improved, due to the reductions in the band gap and effective mass, which are caused by the transition of band alignment. Our works indicate that a controllable band alignment of Cs2PbI2Cl2/Pd2Se3 heterostructure can provide theoretical guidance for the flexible designs of devices with multi-functional applications. [ABSTRACT FROM AUTHOR]

To study the electron transport properties in InGaN channel-based heterostructures, a revised Fang-Howard wave function is proposed by combining the effect of GaN back barrier. Various scattering mechanisms, such as dislocation impurity (DIS) scattering, polar optical phonon (POP) scattering, piezoelectric field (PE) scattering, interface roughness (IFR) scattering, deformation potential (DP) scattering, alloy disorder (ADO) scattering from InGaN channel layer, and temperature-dependent energy bandgaps are considered in the calculation model. A contrast of AlInGaN/AlN/InGaN/GaN double heterostructure (DH) to the theoretical AlInGaN/AlN/InGaN single heterostructure (SH) is made and analyzed with a full range of barrier alloy composition. The effect of channel alloy composition on InGaN channel-based DH with technologically important Al(In,Ga)N barrier is estimated and optimal indium mole fraction is 0.04 for higher mobility in DH with Al0.4In0.07Ga0.53N barrier. Finally, the temperature-dependent two-dimensional electron gas (2DEG) density and mobility in InGaN channel-based DH with Al0.83In0.13Ga0.04N and Al0.4In0.07Ga0.53N barrier are investigated. Our results are expected to conduce to the practical application of InGaN channel-based heterostructures. [ABSTRACT FROM AUTHOR]

The novel two-dimensional (2D) semiconductor, InSe, with tunable band gap and high electron mobility, has attracted increasing research interest. In this work, we demonstrate theoretically the strong geometry confinement in InSe quantum dots (QD) and manipulate their electronic and optical properties using QD shape and external field. The electronic energy levels, density of states, probability density of states and magneto-optical absorption spectra, are calculated by utilizing the tight-binding method with Coulomb interaction in the Hubbard model. In contrast to other 2D materials, e.g. phosphorene, InSe-QDs exhibit distinct features as (a) edge states appear in the bottom of the conduction band regardless of the shapes of InSe-QDs; (b) the edge states are mainly provided by the In atoms at the both armchair and zigzag edges in InSe-QDs; (c) optical gap is distinct from band gap. The rectangular InSe-QDs produce anisotropic optical absorption spectra, whereas hexagonal and triangular InSe-QDs produce isotropic absorption spectra. The applied magnetic field would weaken this anisotropy. [ABSTRACT FROM AUTHOR]

This paper proposes to insert a buried P-type gate (BPT gate) under the channel layer of the recessed MIS-high electron mobility transistor (HEMT) to form a dual-gate HEMT. And through simulation calculation, the device performance is calculated and the working mechanism of the BPT gate is explained in detail. Compared with a conventional AlGaN/AlN/GaN HEMT and a gate-recessed MIS-HEMT, the dual-gate HEMT has a higher breakdown voltage (1126 V) and a larger threshold voltage (1.5 V). The results show that inserting a BPT gate in a gate-recessed MIS-HEMT can increase the threshold voltage and improve the breakdown characteristics. Through the optimization of the device structure, it is found that the combination of the MIS-gate and the Γ-type field plate based on the dual-gate device can obtain a higher breakdown voltage. Its breakdown voltage can reach 3041 V, and the figure of merit is as high as 3.56 GW cm−2. This reveals that the combination of dual-gate and Γ-type field plate has great potential in the manufacture of enhancement-mode and high-voltage power transistors. [ABSTRACT FROM AUTHOR]

AlGaN/GaN heterojunction-based high-electron-mobility transistors (HEMTs) have significant advantages of high carrier concentration, high electron mobility, and large breakdown voltage, and show promising potential as power devices. Being widely used in semiconductor manufacturing, dry etching process is capable of fabricating microstructures and thinning substrate from backside, which is good for developing flexible devices. Here, we investigate the effect of backside dry etching of Si substrate on the physical and electrical properties of AlGaN/GaN HEMTs. The physical properties were characterized by scanning electron microscope, Raman spectra, and x-ray diffraction (XRD). After the dry etching process, the peak red-shift of GaN E2 mode indicates an increase of tensile stress, and the XRD rocking curve of GaN film shows to a certain extent decreased dislocation density. Furthermore, the maximum saturation current density and maximum transconductance of the HEMTs are improved by 21.1% and 25.5%, respectively. The approach of backside dry etching for thinning Si substrate would contribute to the optimization of GaN heterojunction-based devices, and also provide inspirations for the development of flexible and robust power devices. [ABSTRACT FROM AUTHOR]

As third-generation semiconductors, group-III nitrides are promising for high power electronic and optoelectronic devices because of their wide bandgap, high electron saturation mobility, and other unique properties. Inspired by the thickness-dependent properties of two-dimensional (2D) materials represented by graphene, it is predicted that the 2D counterparts of group-III nitrides would have similar properties. However, the preparation of 2D group-III nitride-based materials and devices is limited by the large lattice mismatch in heteroepitaxy and the low rate of lateral migration, as well as the unsaturated dangling bonds on the surfaces of group-III nitrides. The present review focuses on theoretical and experimental studies on 2D group-III nitride materials and devices. Various properties of 2D group-III nitrides determined using simulations and theoretical calculations are outlined. Moreover, the breakthroughs in their synthesis methods and their underlying physical mechanisms are detailed. Furthermore, devices based on 2D group-III nitrides are discussed accordingly. Based on recent progress, the prospect for the further development of the 2D group-III nitride materials and devices is speculated. This review provides a comprehensive understanding of 2D group-III nitride materials, aiming to promote the further development of the related fields of nano-electronic and nano-optoelectronics. [ABSTRACT FROM AUTHOR]

Optoelectronic properties of MoSe2 are modulated by controlled annealing in air. Characterizations by Raman spectroscopy and XPS demonstrate the introduction of oxygen defects. Considerable increase in electron and hole mobilities reveals the highly improved electron and hole transport. Furthermore, the photocurrent is enhanced by nearly four orders of magnitudes under 7 nW laser exposure after annealing. The remarkable enhancement in the photoresponse is attributed to an increase in hole trapping centers and a reduction in resistance. Furthermore, the annealed photodetector shows a fast time response on the order of 10 ms and responsivity of 3 × 104 A/W. [ABSTRACT FROM AUTHOR]

Two dimensional electron gases (2DEGs) realized at GaAs/AlGaAs single interfaces by molecular-beam epitaxy (MBE) reach mobilities of about 15 million cm2 V s−1 if the AlGaAs alloy is grown after the GaAs. Surprisingly, the mobilities may drop to a few millions for the identical but inverted AlGaAs/GaAs interface, i.e. reversed layering. Here we report on a series of inverted heterostructures with varying growth parameters including temperature, doping, and composition. Minimizing the segregation of both dopants and background impurities leads to mobilities of 13 million cm2 V s−1 for inverted structures. The dependence of the mobility on electron density tuned by a gate or by illumination is found to be the identical if no doping layers exist between the 2DEG and the respective gate. Otherwise, it differs significantly compared to normal interface structures. Reducing the distance of the 2DEG to the surface down to 50 nm requires an additional doping layer between 2DEG and surface in order to compensate for the surface-Schottky barrier. The suitability of such shallow inverted structures for future semiconductor-superconductor hybrid systems is discussed. Lastly, our understanding of the improved inverted interface enables us to produce optimized double-sided doped quantum wells exhibiting an electron mobility of 40 million cm2 V s−1 at 1 K. [ABSTRACT FROM AUTHOR]

Three different elements, silicon, selenium, and tellurium, are ion-implanted in gallium arsenide to form a conducting layer that serves as a back-gate to a molecular beam epitaxy overgrown two-dimensional electron gas. While the heavy ion tellurium creates too many defects in the gallium arsenide to form a conducting layer, both silicon and selenium show promising results combined with MBE-grown high-quality 2DEGs. Similar 2DEG mobilities compared to non-implanted reference samples are achieved for both silicon and selenium implanted structures. Individual contacts to the back-gate are challenging. However, silicon implanted structures, annealed before the MBE growth, result in a functional back-gate, and the electron density of the 2DEG can be tuned via the structured back-gate. [ABSTRACT FROM AUTHOR]

Layered molybdenum disulfide (MoS2) is emerging as a promising candidate for novel electronic applications, though the focus has largely been on few-layered thin films and in-layer electrical properties. MoS2 shows various nontrivial departures in its electrical properties in comparison to isotropic crystalline materials, however the understanding of anisotropic properties, particularly of charge carrier mobility in MoS2 flakes, is meagre. We experimentally study inter-layer mobility in mechanically exfoliated MoS2 flakes. The choice of a suitable sandwich device structure enables us to study the inter-layer transport using temperature dependent current–voltage (J–V) and impedance spectroscopy. The separation of peaks in the imaginary part of impedance i.e. Im (Z) spectra due to defects and transport in the space charge limited regime allows measurement of mobility un-encumbered by other effects. We study flakes obtained from both naturally occurring and synthetic crystals. The calculated inter-layer mobility () exhibits temperature dependence with δ = 1.6 and thereby revealing that impurity scattering is the dominant mechanism. A further confirmation that the mobility is limited by charged impurity scattering comes from the observation that it improves for temperatures lower than a characteristic temperature, which marks deionization of donor impurities. Our results provide a direct estimation of the inter-layer mobility in exfoliated MoS2 flakes and would lead to carrier transport engineering and design strategies for applications based on MoS2 flakes. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gases (2DEGs) formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena. While most of the previous works focused on SrTiO3-based 2DEGs, here we took the amorphous-ABO3/KTaO3 system as the research object to study the relationship between the interface conductivity and the redox property of B-site metal in the amorphous film. The criterion of oxide–oxide interface redox reactions for the B-site metals, Zr, Al, Ti, Ta, and Nb in conductive interfaces was revealed: the formation heat of metal oxide, , is lower than –350 kJ/(mol O) and the work function of the metal Φ is in the range of 3.75 eV < Φ < 4.4 eV. Furthermore, we found that the smaller absolute value of and the larger value of Φ of the B-site metal would result in higher mobility of the two-dimensional electron gas that formed at the corresponding amorphous-ABO3/KTaO3 interface. This finding paves the way for the design of high-mobility all-oxide electronic devices. [ABSTRACT FROM AUTHOR]

Resonant tunneling phenomena are explored using armchair graphene nanoribbon (AGNR), which eliminates the lattice mismatch and electron mobility degradation problems of conventional heterostructure resonant tunneling diodes (RTDs). Eight antidote topologies are proposed in this paper. These antidote topologies significantly increase or decrease the band gap of AGNR. Both double barrier quantum well and single barrier quantum well structures have been achieved by putting the antidote-induced AGNRs and pristine AGNRs. A numerical approach with a tight binding model and non-equilibrium Green's function formalism has been used to simulate the quantum phenomena of the device. Current–voltage characteristics of these proposed RTDs show a high peak to valley ratio and low power dissipation with respect to different antidote topologies. Channel length variation effects are investigated in the proposed RTDs, and it is found that the peak to valley ratio, valley current, valley voltage, and power dissipation can be improved by tuning the channel length. These graphene-based RTDs are easy to fabricate and offer more flexibility in terms of peak to valley ratio, valley current, valley voltage, and power dissipation. [ABSTRACT FROM AUTHOR]

Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared optoelectronic devices and high speed transistors, however InN growth is much more challenging compared to other III-N semiconductors. In this study we analysed the impact of pre-growth vicinal c-plane sapphire substrate nitridation on the electrical, optical, and strucutral properties of N-polar InN/InAlN heterostructures and the InN crystal habit. While a short cool-down nitridation phase resulted in a high quality InAlN layer and low quality InN layer, it was the opposite for a long cool-down nitridation phase. A trade-off between the electrical and optical properties was observed: the short nitridation cool-down produced InN layers with a higher electron mobility of 629 cm2 V−1 s−1 and low photoluminescence (PL) emission, and the long one resulted in InN with a ∼21% lower electron mobility of 497 cm2 V−1s−1 but strong PL emission. Also, a very different InN crystal habit was observed for either case. The short nitridation cool-down was conducive to the formation of a continuous layer consisting mostly of coalesced downward-pointing hexagonal pyramids, while the long one led to a layer of upward-pointing hexagonal pyramids. The local decomposition of an AlON layer produced by sapphire nitridation and variations in the InAlN surface morphology resulting in a preferential attraction of growth species and localised change in the surface free energy contributions were most likely responsible for these observations. Our results also suggest N-polar buffer layers are likely to produce coalesced InN layers with a high electron mobility, while metal-polar buffer layers may facilitate the growth of high crystal quality pyramidal InN with a strong optical response. [ABSTRACT FROM AUTHOR]

The influence of dislocation density on the transport properties of high electron mobility transistor (HEMT) structures is reported in this work. Experimental results, obtained on HEMT structures prepared in the same growth run on templates with different dislocation densities, are compared. However, the direct comparison of structures is complicated, since parallel parasitic currents through deeper parts of the heterostructure were observed in samples with lower dislocation density. To suppress this phenomenon, the addition of an AlGaN back barrier (BB) beneath the two dimensional electron gas (2DEG) channel is proposed and optimized and the most suitable design based on both modeling and experimental results is suggested. Subsequently, the comparison of electron mobility in 2DEG for structures with AlGaN BB and different dislocation densities was possible. We show experimentally that lowering the dislocation density considerably increases the electron mobility in 2DEG. It is shown that the dislocation density also has a significant influence on the Fermi level position in GaN. The presented results suggest that reduction of dislocation density can improve the performance of high-frequency GaN HEMT applications. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3), an emerging ultra-wide-bandgap semiconductor, has the desirable properties of a large bandgap of 4.6–4.9 eV, an estimated critical breakdown field of 8 MV cm−1, decent electron mobility of 250 cm2 V s−1 and high theoretical Baliga figures of merit (BFOMs) of around 3000. Bolstered by their capability of an economical growth technique for high-quality bulk substrate, β-Ga2O3-based materials and devices have been highly sought after in recent years for power electronics and solar-blind ultraviolet photodetectors. This article reviews the most recent advances in β-Ga2O3 power device technologies. It will begins with a summary of the field and underlying semiconductor properties of Ga2O3, followed by a review of the growth methods of high-quality β-Ga2O3 bulk substrates and epitaxial thin films. Then, brief perspectives on the advanced technologies and measurements in terms of ohmic contact and interface state are provided. Furthermore, some state-of-the-art β-Ga2O3 photoelectronic devices, power devices and radiofrequency devices with distinguished performance are fully described and discussed. Some solutions to alleviating challenging issues, including the difficulty in p-type doping, low thermal conductivity and low mobility, are also presented and explored. [ABSTRACT FROM AUTHOR]

GaAs compound-based electronics attracted significant interest due to unique properties of GaAs like high electron mobility, high saturated electron velocity and low sensitivity to heat. However, GaAs compound-based electronics demand a significant decrease in their manufacturing costs to be a good competitor in the commercial markets. In this context, copper-based nanoparticle (NP) inks represent one of the most cost-effective metal inks as a proper candidate to be deposited as contact grids on GaAs. In addition, Inkjet-printing, as a low-cost back-end of the line process, is a flexible manufacturing method to deposit copper NP ink on GaAs. These printed copper NP structures need to be uncapped and fused via a sintering method in order to become conductive and form an ohmic contact with low contact resistivity. The main challenge for uncapping a copper-based NP ink is its rapid oxidation potential. Laser sintering, as a fast uncapping method for NPs, reduces the oxidation of uncapped copper. The critical point to combine these two well-known industrial methods of inkjet printing and laser sintering is to adjust the printing features and laser sintering power in a way that as much copper as possible is uncapped resulting in minimum contact resistivity and high conductivity. In this research, copper ink contact grids were deposited on n-doped GaAs by inkjet-printing. The printed copper ink was converted to a copper grid via applying the optimized settings of a picosecond laser. As a result, an ohmic copper on GaAs contact with a low contact resistivity (8 mΩ cm2) was realized successfully. [ABSTRACT FROM AUTHOR]

In this study, we propose a novel, high-conductivity multi-channel heterostructure based on lattice-matched InAlN/GaN channels with modulation-doping-induced two-dimensional electron gases (2DEGs). To facilitate device processing, the channel period thickness was minimized while maintaining a high electron mobility in each channel. We demonstrate a 10-channel heterostructure with a period thickness of 14 nm and a total sheet resistance of 82 Ω □−1. By increasing the doping concentration in each channel, much higher carrier densities per channel were achieved, resulting in an ultra-low sheet resistance of 36 Ω □−1. Furthermore, optimizing the heterostructure design enabled high electron mobilities, up to 1530 cm2 V−1 s−1, independent of the number of channels, by secluding the 2DEG from the barrier interfaces in each channel to avoid both strong interface roughness and ionized impurity scattering. This was achieved by modulation-doping of the GaN channel and the insertion of a GaN interlayer between the InAlN barrier and the AlN spacer. This approach offers a new platform for designing high conductivity heterostructures, where the general trade-off between electron mobility and carrier density can be significantly alleviated. [ABSTRACT FROM AUTHOR]

Two-dimensional layered metal chalcogenides (LMCs) are widely used in battery anode materials, energy conversion, and semiconductor devices, because of their high energy storage characteristics, high thermoelectric characteristics, and large electron mobility. SnSe2 as a kind of LMC has strong nonlinear optical characteristics. However, its research on dissipative system dynamics as a saturable absorber has not been studied. In this work, we obtained SnSe2 nanosheets using lithium ion intercalation and we reported a passively mode-locked fiber laser with SnSe2 as a saturable absorber to achieve the dissipative soliton in a dissipative system. Due to the high third-order nonlinearity of SnSe2, the evolution of square wave pulses from 2 to 16 ns was obtained in a fiber ring cavity. Through adjusting the polarization state, the evolution phenomenon of soliton rain, the soliton rain phenomenon with a spectrum of dual-wavelengths, and a bound state harmonic phenomenon with a frequency of 313 MHz were obtained. Therefore, the strong nonlinear fiber laser based on SnSe2 provides a good platform for study the pulsation, explosion, rainfall and other phenomena. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) semiconductors with desirable bandgaps and high carrier mobility have great potential in electronic and optoelectronic applications. In the present work, 2D M-ScN, H-ScN, and O-ScN are predicted by the swarm-intelligent global structure search method. The low formation energies and high dynamical and thermal stabilities indicate the high feasibility of experimental synthesis of these ScN monolayers. The electronic structure calculations reveal that M-ScN and O-ScN are both direct bandgap semiconductors with the bandgaps of 1.39 and 2.14 eV, respectively, while H-ScN has a large indirect bandgap of 3.21 eV. In addition, both M-ScN and H-ScN exhibit ultra-high electron mobilities (3.09 × 104 cm2 V−1 s−1 and 1.22 × 104 cm2 V−1 s−1, respectively). More notably, O-ScN is found to be a promising 2D auxetic and ferroelastic material. The values of negative Possion's ratios and reversible strain of this monolayer are predicted to be −0.27% and 15%, respectively. [ABSTRACT FROM AUTHOR]

The state-of-the-art perovskite solar cells (PSCs) with SnO2 electron transporting material (ETL) layer displays the probability of conquering the low electron mobility and serious leakage current loss of the TiO2 ETL layer in photoelectronic devices. The rapid development of SnO2 ETL layer has brought perovskite efficiencies >20%. However, high density of defect states and voltage loss of high temperature SnO2 are still latent impediment for the long-term stability and hysteresis effect of photovoltaics. Herein, Nb5+ doped SnO2 with deeper energy level is utilized as a compact ETL for printable mesoscopic PSCs. It promotes carrier concentration increase caused by n-type doping, assists Fermi energy level and conduction band minimum to move the deeper energy level, and significantly reduces interface carrier recombination, thus increasing the photovoltage of the device. As a result, the use of Nb5+ doped SnO2 brings high photovoltage of 0.92 V, which is 40 mV higher than that of 0.88 V for device based on SnO2 compact layer. The resulting PSCs displays outstanding efficiency of 13.53%, which contains an ∼10% improvements compared to those without Nb5+ doping. Our study emphasizes the significance of element doping for compact layer and lays the groundwork for high efficiency PSCs. [ABSTRACT FROM AUTHOR]

In this work, a comprehensive technology computer aided design-based investigation of a buffer-free high electron mobility transistor under proton radiation is presented. With a 37.55% thinner architecture (without thick and highly doped Fe buffer) grown on silicon carbide substrate, this device design improves the two-dimensional electron gas (2DEG) confinement and helps to eliminate the various dispersion effects and buffer leakage. To gain better insight into the buffer-free device architecture, direct current (DC), thermal, and radio frequency (RF) studies are carried out. To establish the various prospects of this device in high-power and space applications, the performance of the device under 1.8 MeV proton radiation environment is systematically studied. A comparison demonstrates that the buffer-free structure under proton radiation with fluence shows a current degradation of 18.68% compared with 72.7% in the case of conventional architecture. The excellent capability of the buffer-free device to confine 2DEG more precisely even under radiation environments can be concluded from the various DC and RF parameters studied. An extensive study of the effects of proton fluences and biases on the RF power amplifier figures of merit was also conducted by carrying out harmonic balance simulations for different radiation setups, which demonstrates excellent performance of the buffer-free structure. [ABSTRACT FROM AUTHOR]

We investigated the influence of the flake thickness for molybdenum disulfide (MoS2) field effect transistors on the effect of a 150 keV high-energy proton beam applied on these devices. The electrical characteristics of the devices with channel thicknesses ranging from monolayer to bulk were measured before and after proton irradiation with a proton fluence of 5 × 1014 cm−2. The subthreshold swing (SS), threshold voltage shift and electron mobility were extracted with the Y-function method after proton irradiation and significant degradation were observed. It is found that, with the increase of layer thickness, mobility degradation and threshold voltage shift both eased, but the SS degradation was insensitive to the MoS2 flake thickness increase. We also demonstrate that the threshold voltage shift is dominated by oxide charges; however, the mobility and SS degradations are mainly affected by the interface traps. Our study will enhance the understanding of the influence of high-energy particles on MoS2-based nano-electronic devices. By increasing the MoS2 flake thickness to a certain extent, one can hopefully find a balance between effectively resisting shift and achieving high mobility and small SS degradation. [ABSTRACT FROM AUTHOR]

This paper reports on the fabrication of an enhancement-mode AlGaN/GaN metal-insulator-semiconductor-high electron mobility transistor with a new barrier epi-layer design based on double Al0.2Ga0.8N barrier layers separated by a thin GaN layer. Normally-off transistors are achieved with good performances by using digital etching (DE) process for the gate recess. The gate insulator is deposited using two technics: plasma enhance chemical vapour deposition (sample A) and atomic layer deposition (sample B). Indeed, the two devices present a threshold voltage (Vth) of +0.4 V and +0.9 V respectively with ΔVth about 0.1 V and 0.05 V extracted from the hysteresis gate capacitance measurement, a gate leakage current below 2 × 10−10 A mm−1, an ION/IOFF about 108 and a breakdown voltage of VBR = 150 V and 200 V respectively with 1.5 µm thick buffer layer. All these results are indicating a good barrier surface quality after the gate recess. The DE mechanism is based on chemical dissolution of oxides formed during the first step of DE. Consequently, the process is relatively soft with very low induced physical damages at the barrier layer surface. [ABSTRACT FROM AUTHOR]

Assessing the position of the Bragg peak (BP) in hadron radiotherapy utilizing prompt-gamma imaging (PGI) presents many challenges in terms of detector physics. Gamma detectors with the capability of extracting the best energy, timing, and spatial information from each gamma interaction, as well as with high detection efficiency and count rate performance, are needed for this application. In this work we present the characterization of a pixel Čerenkov charge induction (CCI) thallium bromide (TlBr) detector in terms of energy and and electron drift time for its potential use in PGI. The CCI TlBr detector had dimensions of 4 × 4 × 5 mm3 and one of its electrodes was segmented in pixels with 1.7 mm pitch. A silicon photomultiplier (SiPM) was optically coupled to one of the faces of the TlBr slab to read out the Čerenkov light promptly emitted after the interaction of a gamma ray. The detector was operated stand-alone and the 1.275 prompt gammas from a 22Na radioactive source were used for the study. The electron drift time was obtained by combining the Čerenkov and charge induction signals and then used as a measure of the depth of interaction. The electron mobility in TlBr was estimated as ∼27 cm2 V−1 s−1. Energy resolutions between 3.4% and 4.0% at 1.275 MeV were obtained after depth-correction. These values improved to 3.0%–3.3% when events with drift times of 3–6 μs were selected. These results show the potential of pixel CCI TlBr detectors to resolve gamma interactions in the detector with mm-like accuracy in 3D and with excellent energy resolution. Previous studies with CCI TlBr devices have shown a timing resolution of <400 ps full width at half maximum when detecting 511 keV gamma rays, therefore, the timing accuracy is expected to improve with the increased energy of the gamma rays in PGI. While other important detector characteristics such as count rate capability remain to be studied, results from this work combined with other preliminary data show pixel CCI detectors can simultaneously provide excellent energy, timing, and spatial resolution performance and are a very promising option for PGI in hadron therapy. [ABSTRACT FROM AUTHOR]

SnO films are prepared by reactive magnetron sputtering under various O2 partial pressures along with post-annealing in air. The results indicate that the O2 partial pressure during reactive sputtering process not only influences the composition of the SnO film but also its texture. For the SnO film deposited under 10% O2 partial pressure, its direct bandgap increases from 2.49 to 2.64 eV with elevating the post-annealing temperature from 250 °C to 400 °C. The above SnO-based channel thin-film transistors (TFTs) exhibit a typical ambipolar feature after post-annealing at ≥250 °C in air. For the TFTs annealed at 300 °C for 30 min, the extracted hole and electron field-effect mobility is 1.48 cm2V−1s−1 and 0.21 cm2V−1s−1, respectively. The performance of both p- and n-type TFTs could be further improved by optimizing fabrication process and post-annealing conditions because of a trade-off between hole and electron mobility. [ABSTRACT FROM AUTHOR]

The effects of Ga composition on the electrical parameters of (Al,Ga)Sb/InAs two-dimensional electron gas have been investigated. The (Al,Ga)Sb/InAs structures are grown on GaAs (001) substrate by molecular-beam epitaxy with various Ga compositions in Al1−xGaxSb bottom barrier. The sheet resistance shows a crossover with the variation of temperature, and the temperature T* corresponding to this crossover decreases with increasing the Ga composition. The temperature dependence of the electron mobility is similar for the samples with different Ga compositions, while the temperature dependence of the carrier density is obviously different. Qualitative analyses reveal that the temperature dependent portion of carrier density is mainly determined by the interface-related donors. A thermal activation model is used to fit the temperature dependence of carrier density, and the fitting results imply that the thermal activation energies of the carriers are significantly affected by the Ga composition. Our results provide useful information for understanding the sources of carriers in the (Al,Ga)Sb/InAs systems, and provide one pathway for the modulation of the temperature dependent carrier density. [ABSTRACT FROM AUTHOR]

The influence of chamber pressure and Si-doping on the growth rate, surface morphology and Hall mobility was investigated for β-Ga2O3 thin films homoepitaxially grown by metalorganic vapor phase epitaxy on Mg-doped β-Ga2O3 (100) substrates with 4° miscut. Transitions from step-bunching to step-flow to 2D island growth modes were achieved by varying the chamber pressure from 10 mbar to 40 mbar and/or by varying the O2/Ga ratio. High-quality β-Ga2O3 homoepitaxial thin films with a high electron mobility of 153 cm2 Vs−1 have been obtained at a chamber pressure of 25 mbar and a growth rate of 3.6 nm min−1. The Si-doped films show electron concentrations in the range of 1 × 1017 to 2 × 1019 cm−3. When increasing the chamber pressure to 40 mbar step-flow growth mode and high charge carrier mobility can only be preserved by adjusting the O2/Ga ratio and increasing the Ar push gas flow. Secondary ion mass spectrometry and Hall measurements for Si and electron concentration, respectively, revealed Si compensation at higher tetraethyl orthosilicate flux. [ABSTRACT FROM AUTHOR]

We report on a systematic analysis of phosphorus diffusion in silicon on insulator thin film via spin-on-dopant process (SOD). This method is used to provide an impurity source for semiconductor junction fabrication. The dopant is first spread into the substrate via SOD and then diffused by a rapid thermal annealing process. The dopant concentration and electron mobility were characterized at room and low temperature by four-probe and Hall bar electrical measurements. Time-of-flight-secondary ion mass spectroscopy was performed to estimate the diffusion profile of phosphorus for different annealing treatments. We find that a high phosphorous concentration (greater than 1020 atoms cm−3) with a limited diffusion of other chemical species and allowing to tune the electrical properties via annealing at high temperature for short time. The ease of implementation of the process, the low cost of the technique, the possibility to dope selectively and the uniform doping manufactured with statistical process control show that the methodology applied is very promising as an alternative to the conventional doping methods for the implementation of optoelectronic devices. [ABSTRACT FROM AUTHOR]

A flexible framework is obtained for enhancing both the thermal and electrical performance of fin field-effect transistor (FinFET) technology. Investigation of the nanoscale heat conduction within a short-channel field-effect transistor can be regarded as an emerging challenge related to future-generation transistors. In this work, we report the electrothermal transport in a 10 nm silicon-on-insulator (SOI) FinFET based on the dual-phase-lag model and modified drift-diffusion motions. We found that electron mobility decreases along the channel due to carrier confinement under higher electric field. In addition, the surface detection temperature indicates that the self-heating process is localized between the source and drain region. As promising results, high-κ metal-oxide and lower thermal boundary resistance can optimize the nanoscale heat transport in the SOI FinFET device. [ABSTRACT FROM AUTHOR]