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Presents a study which examined the germanium incorporation and the growth rate of Si[sub1-x]Ge[subx] films deposited by rapid thermal process very low pressure chemical vapor deposition. Background on the sample material; Description of the experimental setup; Results.

Power Schottky barrier diodes (SBDs) face an inherent trade-off between forward conduction loss and reverse blocking capability. This limitation becomes more severe for ultra-wide bandgap (UWBG) SBDs due to the large junction field. A high Schottky barrier is usually required to suppress the reverse leakage current at the price of an increased forward voltage drop (VF). This work demonstrates a Ga2O3 junction barrier Schottky (JBS) diode that employs the embedded p-type NiO grids to move the peak electric field away from the Schottky junction, thereby allowing for the use of an ultra-low barrier TiN Schottky contact. This JBS diode concurrently realizes a low VF of 0.91 V (at forward current of 100 A/cm2) and a high breakdown voltage over 1 kV, with the VF being the lowest in all the reported vertical UWBG power diodes. Based on the device characteristics measured up to 200 °C, we further analyze the power loss of this JBS diode across a wide range of operational duty cycles and temperatures, which is found to outperform the TiN/Ga2O3 SBDs or NiO/Ga2O3 PN diodes. These findings underscore the potential of low-barrier UWBG JBS diodes for high-frequency, high-temperature power electronics applications. [ABSTRACT FROM AUTHOR]

Using computer‐aided design (TCAD) simulation, the impact of the Fe doping profile, including concentration, decay rate, and depth of the doping region on current‐collapse magnitude (▵CC) in 0.5‐μm gated GaN‐based high electron mobility transistors (HEMTs) is systematically investigated. Accurate simulation models are established and developed to facilitate the fabrication of electronics. It is elucidated that the intricate interplay between trapping and de‐trapping of Fe‐related traps at the gate‐drain edge is responsible for current collapse. The concentration and decay rate of the doping region have a more significant impact on current collapse than the depth. Increased trap state density near two‐dimensional electron gas (2DEG) channel caused by deep‐level acceptors would boost ▵CC. However, a minor dynamic reduction in 2DEG density (nT) induces a relatively small ▵CC. By adjusting the concentration, decay rate, and depth of the doping region, ▵CC of GaN‐based Radio Frequency (RF) HEMTs can be reduced by approximately 50.3 %. The optimized distribution of Fe doping discussed in this work helps to prepare GaN‐based RF HEMTs with a limited current collapse effect. [ABSTRACT FROM AUTHOR]

In this work, fine carrier transport and recombination processes in p-NiO gate AlGaN/GaN high electron mobility transistors were investigated by analyzing their electroluminescence under forward gate bias, with photoluminescence spectrum as a reference. Red luminescence with a peak of 1.9 eV was captured when the gate bias voltage exceeded 4 V, which was verified to originate from the tunneling enhanced interface recombination of injected holes from the gate metal and spilled electrons from the 2DEG channel at the type-II band aligned p-NiO/AlGaN heterostructure interface. Under higher gate bias voltage, holes were further injected into the GaN buffer layer, producing ultraviolet luminescence and yellow luminescence, corresponding respectively to the band edge emission and defect-assisted radiative recombination of GaN. Threshold voltage shift measurements under forward gate bias were conducted to further investigate the carrier transport and recombination processes. [ABSTRACT FROM AUTHOR]

In this Letter, we investigated the electrostatic control capability and gate reliability of the BaTiO3 integrated AlGaN/GaN HEMTs. The fabricated HEMT exhibits a high peak maximum transconductance of 141 mS/mm, a large ON/OFF current ratio of 4.1 × 109, and a small subthreshold swing of 70.6 mV/dec, attributed to the gate leakage suppression and prominent gate coupling. These parameters demonstrate that the HEMT device with extreme permittivity BaTiO3 dielectric has the excellent electrostatic control capability. A high breakdown voltage of 1348 V was also achieved thanks to the screening of the negative gate image charges and the resulting improvement of electric field distribution by using double-layer BaTiO3 with the wrapped gate structure. Furthermore, gate bias step-stress and pulse I–V measurements show that the device exhibits a small VTH shift of 0.06 V at 2 V bias stress and a slight current collapse of ∼2.7% accompanied with a 6.0% RON increment at a quiescent drain bias VDSQ = 30 V, which benefits from the high quality of the dielectrics/AlGaN interface with Dit of 8.87 × 1012 eV−1/cm2. These findings elucidate the immense potential of extreme permittivity dielectrics engineering in achieving high-performance AlGaN/GaN power electronic devices. [ABSTRACT FROM AUTHOR]

High‐sensitivity photodetection capability has become an indispensable requirement for detecting feeble solar‐blind ultraviolet (UV) light. Micro‐nano metallic metasurface structures are employed to enhance the detector photoelectric performances. However, existing approaches are confronted with bottlenecks of structure simplification and efficacy mediocrity. Here, a distinctive diamond solar‐blind UV photodetector with a synthetic multistage‐concentric‐annulus (MCA) architecture metasurface is reported, which is prepared through a facile and peculiar Fraunhofer diffraction technique. The detector achieves an excellent photo‐to‐dark‐current ratio of 2.4×108 and maintains an extremely low dark current on the order of pA magnitude. The intrinsic response peak and resonance absorption phenomenon in solar‐blind UV are evident from the optical properties. Moreover, the surface potential distribution intuitively reveals that plasmon resonance enhances the UV scattering and absorption cross sections, thus facilitating the photogeneration of carriers. Meanwhile, it expressly demonstrates that multi‐level dipole interaction in the MCA structure accelerates the separation and extraction of electron–hole pairs through enhancing the localized electric field intensity. In addition, a wide range of variable temperature measurements further prove the device possesses capacity for working in extreme environments. This photodetection technology by virtue of a delicate and viable diffraction metasurface is anticipated to provide a leap forward for future applications in wide‐band‐gap semiconductor UV detectors. [ABSTRACT FROM AUTHOR]

In general, β-Ga2O3 films with (2¯01) out-of-orientation have been widely obtained and reported on (0001) sapphire substrates by various growth methods. In this paper, the unusual (3¯10)-oriented β-Ga2O3 films have been epitaxially grown on (0001) sapphire substrates with high crystal-quality under Ga-rich conditions by halide vapor phase epitaxy (HVPE). The out-of-plane epitaxial relationship as (3¯10) β-Ga2O3//(0001) α-Al2O3 has been confirmed by XRD and HRTEM analysis. Under most growth conditions, β-Ga2O3 films exhibit the coexistence of (3¯10) and (2¯01) out-of-plane orientation domains, and increasing the growth temperatures and HCl flow-rates can enhance the growth of (3¯10)-oriented β-Ga2O3. Off-angled (0001) sapphire substrates with off-angles (Δa) toward 〈112¯0〉 have been introduced to control the in-plane domains. It was indicated that the (2¯01)-oriented domains have been gradually eliminated with increasing the off-angles, and pure (3¯10)-oriented β-Ga2O3 films with the best crystal quality reported so far have been obtained while the off-angle was ∼7°. The decrease of the domain boundaries and defects caused by the in-plane rotational domains have led to the improvement of the crystal quality of the as-grown films. [ABSTRACT FROM AUTHOR]

Amplification of weak ultraviolet signals has always been a challenging issue to design and fabricate high-performance ultraviolet photodetectors. Here, we observe a distinctive microplasma breakdown behavior in AlGaN-based ultraviolet avalanche photodiodes with artificial mesa architecture. At 107 V breakdown voltage, the photocurrent increases sharply whereas dark current intriguingly remains at the extremely low level of 0.1 nA as the applied voltage increases. Simultaneously, a significant blue luminescence phenomenon is observed at the mesa edge of photodiode at breakdown voltage, indicating the occurrence of microplasma breakdown. Ultimately, the microplasma avalanche photodiode achieves a record-high avalanche gain of 3 × 106 with light–dark current ratio readily exceeding 107. Kelvin probe force microscopy was employed to reveal the physical mechanism of localized avalanche breakdown induced by photoelectric effects and elaborate the microplasma discharge process, which is related to surface states. The unprecedented detection mode of photocurrent triggering avalanche events while remaining low dark current is anticipated to effectively shield the background noise and amplify ultraviolet signals. It is worth further research to explore its possibility on high-sensitivity ultraviolet photodetection. [ABSTRACT FROM AUTHOR]

Low-threshold lasing under pulsed optical pumping is demonstrated in GaN-based microrod cavities at room temperature, which are fabricated on the patterned sapphire substrates (PSS). Because the distribution of threading dislocations (TDs) is different at different locations, a confocal micro-photoluminescence spectroscopy (μ-PL) was performed to analyze the lasing properties of the different diameter microrods at the top of the triangle islands and between the triangle islands of the PSS substrates, respectively. The μ-PL results show that the 2 μm-diameter microrod cavity has a minimum threshold of about 0.3 kW/cm2. Whispering gallery modes (WGMs) in the microrod cavities are investigated by finite-difference time-domain simulation. Combined with the dislocation distribution in the GaN on the PSS substrates, it is found that the distribution of the strongest lasing WGMs always moves to the region with fewer TDs. This work reveals the connection between the lasing modes and the dislocation distribution, and can contribute to the development of low-threshold and high-efficiency GaN-based micro-lasers. [ABSTRACT FROM AUTHOR]

Non-polar m-plane GaN terahertz quantum cascade laser (THz-QCL) structures have been studied. One is traditional three-well resonant-phonon (RP) design scheme. The other is two-well phonon scattering injection (PSI) design scheme. The peak gains of 41.8 and 44.2 cm−1 have been obtained at 8.2 and 7.7 THz respectively at 300 K according to the self-consistent non-equilibrium Green's function calculation. Different from the usual GaAs two-well design, the upper and lower lasing levels are both ground states in the GaN quantum wells for the PSI scheme, mitigating the severe broadening effect for the excited states in GaN. To guide the fabrication of such devices, the doping effect on the peak gain has been analyzed. The two designs have demonstrated distinct doping density dependence and it is mainly attributed to the very different doping dependent broadening behaviors. The results reveal the possibility of GaN based THz-QCL lasing at room temperature. [ABSTRACT FROM AUTHOR]

The generation of p-type GaN through ion implantation is an attractive proposition in the massive production of GaN-based bipolar devices, whereas the removal of implantation induced lattice disturbances and defects is a difficult exercise and hampers the conversion of conductivity in GaN. Pulsed laser annealing is an effective annealing technique to recover lattice crystallinity and activate dopants with the preserved implanted profile. In this work, the effect of pulsed laser annealing on structural and optical recovery in high-dose magnesium (Mg) ion-implanted GaN has been investigated. The structural evolution and vibrational dynamics indicate an obvious structural recovery and partial strain release of Mg-implanted GaN during the pulsed laser annealing process, with a threshold laser fluence of 400 mJ/cm2, while rough surface structures are a result of the regrowth mechanism similar to liquid phase epitaxy. The enhanced donor–acceptor transition at 3.35 eV after pulsed laser irradiation is a sign of the effective activation of Mg from interstitial sites into the substitution of Ga ions. These results suggest that further optimization of the laser annealing technique has promising potential to manipulate the p-type conductivity of Mg-implanted GaN and to be implemented in GaN bipolar devices for practical applications. [ABSTRACT FROM AUTHOR]

Regular resonance modes in GaN-based polygonal microdisks are investigated by simulations and photoluminescence measurements. Based on a standard GaN-based blue light emitting diode wafer on a Si substrate, hexagonal and octagonal microdisks with similar dimensions are fabricated. Whispering gallery-like modes and Fabry–Pérot modes in the polygonal microcavities are pictured by theoretical calculations. All resonant modes in the polygonal microdisks are confined along regular and isolated orbits. The resonant emission from the hexagonal and octagonal microdisks has been achieved at room temperature, which presents regular and ordered resonant emission peaks. The regularly varied mode spacing of the polygonal microdisks provides potential application in multiple-channel optic communication. The distinctive geometric structural features and mode characteristics make the polygonal microdisks greatly superior in terms of mode control and mode selection. [ABSTRACT FROM AUTHOR]

A two-dimensional hole gas (2DHG) induced by polarization charges at the GaN/AlGaN hetero-interface is attracting much attention because of its potential to develop p-channel transistors required for GaN complementary logic integrated circuits. This platform is compatible with commercial AlGaN/GaN n-channel electronics, but the performance of GaN p-channel transistors has been far behind. In this work, 2DHGs in GaN/AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy have been investigated. The Al composition of the AlGaN barrier has been pushed as high as possible without obvious strain relaxation, and the record high 2DHG sheet density and conductivity on the GaN/AlGaN/GaN platform have been obtained. By adopting a parallel conduction model, a dependent relationship of the 2DHG density on temperature has been extracted. The temperature dependent Hall-effect results have demonstrated that the 2DHG density boosts by 75 times and 46 times at room temperature and 77 K, respectively, when the Al composition is pushed from 0.18 to 0.45 for the AlGaN barriers. The 2DHG sheet density reaches 3.6 × 1013 and 2.1 × 1013 cm−2 at room temperature and 77 K, respectively, and the lowest sheet resistance is 8.9 kΩ/□ at 77 K. Such a 2DHG is beneficial for fabrication of p-channel GaN transistors with lower on-resistance on the already-industrialized platform. [ABSTRACT FROM AUTHOR]

Metal-semiconductor-metal (MSM) architectures are popular for achieving high-responsivity Ga2O3 solar-blind photodetectors (SBPDs), however, the hot-electron-induced internal photoemission (IPE) effect restricts their detecting performance. Herein, we demonstrate the rational design of an Al/Al2O3/Ga2O3 metal–insulator-semiconductor (MIS) SBPD that has merits of enhanced responsivity, suppressed sub-gap response and ultralow dark current based on the simulation results obtained using Lumerical software. For the cylindrical patterned detectors with Al/Al2O3/Ga2O3 MIS structures, the optimized dimensions of Al electrodes with a conformed ultra-thin (2 nm) Al2O3 layer support the surface plasmon polariton resonances at 250 nm, thus improving the photoresponsivity to 74 mA W−1. Furthermore, the sandwiched Al2O3 layer lifts the barrier for hot electrons in electrodes, which significantly suppresses the IPE-induced sub-gap photoresponse by more than 105 in magnitude with respect to the Al/Ga2O3 MSM counterpart. Optical and electrical field distributions are overlapped in cylindrically patterned MIS detectors, simultaneously improving the excitation and collection efficiencies of excess carriers and resulting in the 103-boosted rejection ratio. [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]

β -Ga2O3 films have been prepared on (0001) sapphire substrates with different off-axis angles toward $?> < 11 2 ˉ 0 > by sol â€" gel method and the solar-blind ultraviolet photodetectors (PDs) with metal-semiconductor-metal structure have been fabricated on these films. The effects of off-angled sapphire substrates on the surface morphology and crystal quality of β -Ga2O3 films have been systematically investigated. All the results indicate that to some extent the larger off-angled sapphire substrate could lead to the smoother surface morphology and higher crystal quality of β -Ga2O3 films. Reduction in the numbers of in-plane rotational domains for β -Ga2O3 films on off-angled substrates may result in the above-mentioned improvement, which have been confirmed by x-ray diffraction Ď• -scan. β -Ga2O3 film grown on ∼7° off-angled sapphire substrate has ( 400) preferred orientation with the single-domain growth mode. Besides, the performance of β -Ga2O3 PDs fabricated on different off-angled substrates show the same trend with changing the off-axis angles. The β -Ga2O3 PD fabricated on ∼7° off-angled sapphire substrate has excellent optical characteristics with large photocurrent to dark current ratio of 430.53 and high UVâ€"visible rejection ratio of 1.42 Ă— 103. These results would be helpful for improving the crystal-quality of hetero-epitaxy β -Ga2O3 films by using off-angled sapphire substrates and fabricating the cost-effective mass-producible solar-blind ultraviolet PDs by solâ€"gel method. [ABSTRACT FROM AUTHOR]

The authors demonstrate a Bull’s eye cavity design that is composed of circular Bragg gratings and micropillar optical cavity in 4H silicon carbide (4H-SiC) for single photon emission. Numerical calculations are used to investigate and optimize the emission rate and directionality of emission. Thanks to the optical mode resonances and Bragg reflections, the radiative decay rates of a dipole embedded in the cavity center is enhanced by 12.8 times as compared to that from a bulk 4H-SiC. In particular, a convergent angular distribution of the emission in far field is simultaneously achieved, which remarkably boost the collection efficiency. The findings of this work provide an alternative architecture to manipulate lightâ€"matter interactions for achieving high-efficient SiC single photon sources towards applications in quantum information technologies. [ABSTRACT FROM AUTHOR]

In this Letter, we report on the enhanced radio frequency (RF) performance in sub-micrometer scaled β-Ga2O3 tri-gate FinFETs. With a 200-nm-thick β-Ga2O3 bulk channel and a 0.35 μm gate length, the FinFETs exhibit an improved current-gain cutoff frequency of 5.4 GHz and a maximum oscillation frequency of 11.4 GHz, which are 20% and 58% improved with respect to the planar counterpart, respectively. The improved RF performance results from the enhanced gate control capability and the suppressed short-channel effects, as evidenced by the improved pinch-off characteristics, the improved transconductance, and the suppressed output conductance. It suggests that the tri-gate multi-fin architecture is a promising strategy to break the scaling limitation of the gate-channel aspect ratio toward high-performance β-Ga2O3 RF MOSFETs. [ABSTRACT FROM AUTHOR]

AlGaN nanorods have attracted increasing amounts of attention for use in ultraviolet (UV) optoelectronic devices. Here, self-assembled AlGaN nanorods with embedding quantum disks (Qdisks) were grown on Si(111) using plasma-assisted molecular beam epitaxy (PA-MBE). The morphology and quantum construction of the nanorods were investigated and well-oriented and nearly defect-free nanorods were shown to have a high density of about 2 × 1010 cm−2. By controlling the substrate temperature and Al/Ga ratio, the emission wavelengths of the nanorods could be adjusted from 276 nm to 330 nm. By optimizing the structures and growth parameters of the Qdisks, a high internal quantum efficiency (IQE) of the AlGaN Qdisk nanorods of up to 77% was obtained at 305 nm, which also exhibited a shift in the small emission wavelength peak with respect to the increasing temperatures during the PL measurements. [ABSTRACT FROM AUTHOR]

Nonpolar ( 11 2 ÂŻ 0 ) plane In x Ga1âˆ' x N epilayers comprising the entire In content (x) range were successfully grown on nanoscale GaN islands by metal-organic chemical vapor deposition. The structural and optical properties were studied intensively. It was found that the surface morphology was gradually smoothed when x increased from 0.06 to 0.33, even though the crystalline quality was gradually declined, which was accompanied by the appearance of phase separation in the In x Ga1âˆ' x N layer. Photoluminescence wavelengths of 478 and 674 nm for blue and red light were achieved for x varied from 0.06 to 0.33. Furthermore, the corresponding average lifetime (Ď„ 1/ e ) of carriers for the nonpolar InGaN film was decreased from 406 ps to 267 ps, indicating that a high-speed modulation bandwidth can be expected for nonpolar InGaN-based light-emitting diodes. Moreover, the bowing coefficient (b) of the ( 11 2 ÂŻ 0 ) plane InGaN was determined to be 1.91 eV for the bandgap energy as a function of x. [ABSTRACT FROM AUTHOR]

Identifying defects/traps is of vital importance for the implementation of high-performance Ga2O3 power devices. In this work, majority and minority carrier traps in beta-gallium oxide ($\beta $ -Ga2O3) have been investigated and identified by means of deep level transient spectroscopy (DLTS) in Ni/ $\beta $ -Ga2O3 Schottky barrier diode (SBD) and NiO/ $\beta $ -Ga2O3 p+-n heterojunction diode (HJD). For both diodes, a dominant energy level of majority carrier (electron) trap states is determined to be ${E}_{C}-$ (0.75–0.79) eV with a concentration of (2.4–4.1) $\times 10^{{13}}$ cm $^{-{3}}$. Meanwhile, an additional trapping level at ${E}_{V} +0.14$ eV with a concentration of 1.2 $\times 10^{{14}}$ cm $^{-{3}}$ yield is present in NiO/ $\beta $ -Ga2O3 bipolar HJD but absent in the Ni/ $\beta $ -Ga2O3 SBD unipolar counterpart. The detection of such minority carrier traps originates from the hole injection through trap-assisted tunneling (TAT) from $\text{p}^{+}$ -NiO to $\beta $ -Ga2O3. The bias- and frequency-dependent DLTS characteristics identify that such shallow-level minority carrier traps are located in the $\beta $ -Ga2O3 bulk region rather not interfacial states at the NiO/ $\beta $ -Ga2O3 heterointerface. The identification of both majority and minority carrier traps in this work may shed light on the in-depth understanding of carrier transport mechanisms in Ga2O3-based unipolar and bipolar power devices. [ABSTRACT FROM AUTHOR]

The technical progress of Ga2O3 power diodes is now stuck at a critical point where a lack of performance evaluation and reliability validation at the system-level applications seriously limits their further development and even future commercialization. In this letter, by implementing beveled-mesa NiO/Ga2O3 p–n heterojunction diodes (HJDs) into a 500-W power factor correction (PFC) system circuit, high conversion efficiency of 98.5% with 100-min stable operating capability has been demonstrated. In particular, rugged reliability is validated after over 1 million times dynamic breakdown with a 1.2-kV peak overvoltage. Meanwhile, superior device performance is achieved, including a static breakdown voltage (BV) of 1.95 kV, a dynamic BV of 2.23 kV, a forward current of 20 A (2 kA/cm2 current density), and a differential specific on-resistance of 1.9 mΩ·cm2. These results indicate that Ga2O3 power HJDs are developing rapidly with their own advantages, presenting the enormous potential in high-efficiency, high-power, and high-reliability applications. [ABSTRACT FROM AUTHOR]

With a reverse p-n junction in the gate stack design, this work demonstrates a 1.2 kV/25 A normally off p-n junction/AlGaN/GaN high-electron mobility transistor (PNJ-HEMT). Benefiting from the robust gate terminal, the PNJ-HEMT exhibits a large gate breakdown voltage of 18.2 V and a positive threshold voltage of 1.7 V, enabling a wide gate-bias window. Thereafter, with an applicable VGS of 10 V, the transient switching characteristics in nanosecond timescale (11.7-ns rise time and 10.5-ns fall time) and notable immunity to dynamic Ron degradation, as well as record-high dynamic breakdown voltage (1.62 kV) under transient overvoltage have been demonstrated. In particular, rugged reliability is validated after over 1-million times dynamic breakdown with a 1.5-kV peak overvoltage. To the best of our knowledge, this is the first demonstration of high-VGS (10 V) GaN HEMT's circuit-level operating capability with considerable reliability, and has well exceeded the VGS limit of 5–7 V in conventional p-GaN gate-terminal devices, thus possessing great potentials in high-power, high-frequency, and high-reliability applications. [ABSTRACT FROM AUTHOR]

Normally off AlGaN/GaN high electron mobility transistors with a p-type gate are promising for power switching applications, with advantages of low energy consumption and safe operation. In this work, p-NiO is employed as a gate stack, and the interfacial reconstruction and band structure modification at the p-NiO/AlGaN interface have been demonstrated to manipulate channel transport of AlGaN/GaN high electron mobility transistors by post-annealing. In addition to achieving a positive threshold voltage of 0.6 V and a large saturation output current of 520 mA/mm, we found that the gate leakage and On/Off drain current ratio can be improved significantly by more than 104 due to the p-NiO/AlGaN interfacial reconstruction. However, high annealing temperature also results in an increasing ON-resistance and a dramatically increased knee voltage (VK), which can be attributed to the formation of an ultra-thin γ-Al2O3 layer and the substitution of O on N site as a shallow donor at the p-NiO/AlGaN interface confirmed by experimental analyses. Theoretical calculations indicate that such interface reconstruction facilitates an additional potential well at the p-NiO/AlGaN interface to which electrons are spilled out from a two-dimensional electron gas channel under high forward gate voltage, resulting in the increased VK. Finally, an optimized annealing condition was confirmed that can eliminate this increased VK phenomenon and simultaneously remain these significantly improved device performances. These findings provide deep understanding of the performance manipulation of AlGaN high electron mobility transistors, which is very important for engineering the p-NiO/AlGaN interface toward high-performance and stable devices. [ABSTRACT FROM AUTHOR]

The electrical and optical properties of Ag/p–GaN contacts have been investigated as a function of the annealing temperature, oxygen concentration, and annealing time. Specific contact resistance (ρc) values as low as 1.2 × 10–4 Ω·cm2 were obtained from the Ag/p–GaN contact annealed at 400 °C for 60 s in ambient O2/N2 (1:10). We found that the participation of oxygen improves the formation of ohmic contacts. Oxygen might remove the H in Mg–H complexes to activate the Mg acceptors and enhance Ga out-diffusion to form an Ag–Ga solid solution. We also found that the reflectivity of the Ag layer decreases with increasing annealing temperature in the O2-containing ambient environment. Thus, an optimal annealing condition of Ag/p–GaN for blue and green LEDs is suggested based on these results. We also used the suggested annealing conditions to form ohmic contacts on DUV LEDs and achieved good electrical performance. The forward voltages of UVC LEDs fabricated with annealed Ag contacts were 6.60 V (7.66 V) at a 40 mA (100 mA) injection current. [ABSTRACT FROM AUTHOR]

Ga2O3 power diodes with high voltage/current ratings, superior dynamic performance, robust reliability, and potentially easy-to-implement are a vital milestone on the Ga2O3 power electronics roadmap. In this letter, a better tradeoff between fast reverse-recovery and rugged surge-current capability has been demonstrated in NiO/Ga2O3 p-n heterojunction diodes (HJDs). With the double-layered p-NiO design, the HJD exhibits superior electrostatic performances, including a high breakdown voltage of 1.37 kV, a forward current of 12.0 A with a low on-state resistance of 0.26 Ω, yielding a static Baliga's figure of merit (FOM) of 0.72 GW/cm2. Meanwhile, the fast switching performance has been observed with a short reverse recovery time in nanosecond timescale (11 ns) under extreme switching conditions of di/dt up to 500 A/μs. In particular, for a 9-mm2 HJD, a large surge current of 45 A has also been obtained in a 10-ms surge transient, thanks to the conductivity modulation effect. These results are comparable with those of the advanced commercial SiC SBDs and have significantly outperformed the past reported Ga2O3 HJDs, fulfilling the enormous potential of Ga2O3 in power applications. [ABSTRACT FROM AUTHOR]

In this letter, we achieved significantly enhanced avalanche ruggedness and surge current capability in GaN junction barrier Schottky (JBS) diode for highly reliable power operation. Based on the selective Mg-ion implantation technology, the GaN JBS diode obtains superior electrostatic performances, including 830-V breakdown voltage, 150-mΩ specific on-state resistance, and 0.5-V turning on voltage. Meanwhile, zero reverse recovery behaviors are observed even under extreme switching conditions of 600 V/10 A. During the reliability evaluation in the inductive load circuits, crucial avalanche capability with avalanche breakdown voltage over 965 V, avalanche energy up to 57.8 mJ, and more than 10 000 repetitive avalanche breakdown events are demonstrated. Together with the surge current tolerance up to 65 A and surge energy of 6.0 J, a large safe-operation-area under both forward and reverse inductive spikes is realized for the GaN-based rectifier. [ABSTRACT FROM AUTHOR]

In this article, the hydrogen-terminated diamond metal-oxide-semiconductor field effect transistors (MOSFETs) which can operate at high frequency of 10 GHz are demonstrated. The devices were fabricated with a 50 nm Al2O3 gate insulator and a 350 nm Si3N4 passivation layer, which is compatible with the process of monolithic microwave-integrated circuits (MMICs). The device with gate length of 0.35 $\mu \text{m}$ shows a high drain current density of −561 mA/mm. The RF small signal characteristics and power output performances at 10 GHz for the devices with different gate widths have been investigated. With the gate width increased from 100 to 200 $\mu \text{m}$ , the extrinsic maximum frequency of oscillation ${f} _{\text {max}}$ is slightly decreased from 23 to 21 GHz, whereas the output power density at 10 GHz is improved from 1.05 to 1.26 W/mm, with associated power added efficiency increased from less than 5% to 20.77%. Comparing with the devices fabricated by the self-aligned gate process, the power output performance is significantly improved, indicating it is a promising method to fabricate high power and high frequency diamond MOSFETs by using the thick Si3N4 passivation technique. [ABSTRACT FROM AUTHOR]

In this work, gate-first technology was developed in an AlGaN/GaN high-electron-mobility transistor (HEMT) based on a high-quality in situ SiNx gate dielectric, targeting for high-stability power applications. The effect of the high-temperature annealing process on the Ni/SiNx gate stack was systematically investigated. Almost the same basic electrical performances were observed from gate-first and gate-last processed devices. Furthermore, the annealing-like effect on the gate-stack-located trap states was revealed in gate-first devices with obvious enhancement in threshold voltage stability, validating the high compatibility of the in situ SiNx technology with the gate-first GaN HEMT technology. [ABSTRACT FROM AUTHOR]

(01)-oriented β-Ga2O3 films have been grown on (0001) sapphire substrates using the halide vapor phase epitaxy method. The as-grown β-Ga2O3 films exhibit highly textured with domain-like surface morphologies and the root-mean-square roughness is measured at 6.2 nm using atomic force microscopy. The microstructure characteristics of the β-Ga2O3 film have been investigated comprehensively to understand the origin for the domain-like morphologies. Two in-plane rational domains with mirror-symmetrical atomic arrangement have been identified along the [010] axis of β-Ga2O3 by high resolution transmission electron microscopy, which are caused by the (0001) sapphire substrate symmetry. Various defects, including twinned crystals, inversion domains and domain boundaries etc, have been observed, leading to the rough surfaces and poor crystalline quality of β-Ga2O3 grown on non-angled (0001) sapphire substrate. Schematic diagrams and the oxygen atomic arrangements of β-Ga2O3 on ∼7° off-angled (0001) sapphire substrate toward the 〈11 0〉 plane were proposed to illustrate the in-plane quasi-epitaxial relationships between the β-Ga2O3(400) film and the sapphire (11 3) substrate, and to explain the single domain growth mechanism. The results would be helpful for improving the surface morphologies and crystalline quality of heteroepitaxial Ga2O3 films. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistors (HEMTs) have demonstrated their extraordinary potential in developing solid-state microsensors for detecting gases, metal ions, anions, biomolecules, and other substances due to their excellent chemical stability, high surface charge sensitivity, high temperature-tolerance performance, and low power consumption characteristics. In this paper, only three types of AlGaN/GaN HEMT-based sensors used for detecting the pH value, heavy metal ions, and harmful anions, which are suitable for water quality monitoring, will be discussed. First, we introduce the structural design, detection principle, and fabrication processes of AlGaN/GaN HEMT-based sensors. Then, surface functionalization methods for the gate region, sensing mechanisms, and the sensitivity and selectivity performances based on different gate region treatments are reviewed and analyzed. Finally, some challenging problems that hinder the practical application of the sensors are proposed. [ABSTRACT FROM AUTHOR]

The spontaneous emission rate into Surface Plasmon Polariton (SPP) mode for the InGaN/GaN quantum well (QW) with SP coupling is presented taking into account the electron and hole band structures, the photon density of states, and evanescent fields of SPP. The optical properties of SP-enhanced InGaN QW structure with different QW layer number are investigated in detail by using the formula. It is observed that the energy of electron-hole pairs in the InGaN QW can be efficiently transferred into the SPP modes which will induce the significantly enhancement of the internal quantum efficiency (IQE) of SP-enhanced light emitting diodes (LEDs), especially for the original IQE in the range of 6%-25%. Furthermore, the distribution of electron and hole densities in each well layer can evidently affect the Purcell enhancement factor due to the distance dependence of the intensity of SP-QW coupling. The numerical results also indicate that the SP-enhanced LED can suppress the efficiency droop effect as long as the extraction efficiency of SPP mode is enough large. [ABSTRACT FROM AUTHOR]

A back-illuminated heterostructure AlGaN avalanche photodiode (APD) was fabricated with a separate absorption and multiplication (SAM) structure. The SAM structure is able to modulate the electric field distribution of the photodetector and induce a single carrier to trigger an avalanche event. The fabricated p-i-n-i-n APD exhibited a superior maximum gain of 1.8 × 105 at 70 V and distinct solar-blind responsivity peak at 280 nm. However, before the avalanche occurs, the SAM APD needs to be reached through for facilitating carrier transport. By investigating the capacitance characteristics of the SAM APD, the reach-through behavior was directly observed. The capacitance of the detector demonstrated evident declining trends with the applied voltage in the range of 18 to 24 V at different frequencies. The simulated electric field and energy band also revealed that the absorption region was initially reached through at 18 V reverse bias, corresponding to the depletion of n-type interlayer into the absorption region. Meanwhile, there were large differences in capacitances between low and high frequencies, which indicated the effects of impurity and defect states. These findings explicitly reveal the reach-through mechanism of the SAM APD, which is beneficial to the better understanding of device physics and further APD design. [ABSTRACT FROM AUTHOR]

Resonance effects caused by the photon–electron interaction are a focus of attention in semiconductor optoelectronics, as they are able to increase the efficiency of emission. GaN-on-silicon microdisks can provide a perfect cavity structure for such resonance to occur. Here we report GaN-based microdisks with different diameters, based on a standard blue LED wafer on a Si substrate. A confocal photoluminescence spectroscopy is performed to analyze the properties of all microdisks. Then, we systematically study the effects of radial modes and axial modes of these microdisks on photon–electron coupling efficiency by using three-dimensional finite-difference time-domain simulations. For thick microdisks, photon–electron coupling efficiency is found to greatly depend on the distributions of both the radial modes and the axial modes, and the inclined sidewalls make significant influences on the axial mode distributions. These results are important for realization of high-efficiency resonant emission in GaN-based microcavity devices. [ABSTRACT FROM AUTHOR]

Electrically driven hybrid organic/inorganic white light‐emitting diodes (WLEDs) with low‐cost, easy fabrication, and excellent electroluminescence (EL) performance have attracted tremendous attention recently. However, many issues, especially imbalanced carrier injection, have limited their development, so further research is needed. Herein, 4,4′‐cyclohexane‐1,1‐diylbis[N,N‐bis(4‐methylphenyl)aniline] (TAPC) with a large bandgap is introduced as a multifunctional hole transport layer (MHTL) for efficient hybrid organic/inorganic WLEDs. Optimized hybrid WLEDs with TAPC are achieved with a peak current efficiency of 20.6 cd A−1 and a near purity white light with color coordinates of (0.32, 0.33). They exhibit better EL performance than those without TAPC. This proves that an optimized TAPC layer can effectively reduce electron overflow and improve hole injection to acquire much better charge balance in the emitting layers. Such good results will significantly promote the design and fabrication of phosphor‐free WLEDs with high performance. [ABSTRACT FROM AUTHOR]

Herein, InGaN/GaN multiple quantum well (MQW) nanowire ensembles grown on Si (111) substrates by plasma‐assisted molecular beam epitaxy (PA‐MBE) are investigated. Well‐oriented InGaN/GaN nanowires with perfect wurtzite crystal structure can be achieved by optimizing the growth parameter of bottom GaN nanowires. The morphology of the nanowires is strongly influenced by the AlN seeding layer growth time as well as the Ga/N flux ratio and by introducing excessive In flux and relatively higher quantum barrier (QB) growth temperatures. Strong emission from InGaN/GaN nanowires can be achieved by varying InGaN growth temperatures to change the incorporation of indium, therefore tuning the emission spectra from violet to amber. The observations from transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) mapping prove the high quality of MQWs with sharp interfaces and the uniform indium distribution in InGaN QWs. [ABSTRACT FROM AUTHOR]

Screw dislocations are generally considered to be one of the main causes of GaN-based device leakage, but so far, nearly no reports have focused on the effects of open-core screw dislocations on device leakage currents experimentally. In this paper, we use a conductive atomic force microscope to characterize the electronic properties of threading dislocations (TDs) in the GaN layer. The full-core screw dislocations and mixed dislocations are found to provide conductive paths for device leakage currents. In terms of the contribution to device leakage currents, the edge and open-core screw dislocations have smaller effects than the full-core screw dislocations and mixed dislocations. We use isotropic linear elasticity theory and density functional theory calculations to model the core atomic structures of TDs and calculate the corresponding electronic structures. The results show that screw dislocations with full-core structures are found to introduce both deep and shallow energy states within the energy gap dispersedly, while the open-core screw dislocations and the most edge dislocations introduce only shallow energy states. The calculated electronic structures of each type of dislocation are systematically compared and correlated with experimental observations. Our findings demonstrate that full-core screw dislocations and mixed dislocations in the GaN layer have a far more detrimental impact on device leakage than edge and open-core screw dislocations. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN)-based nanowires (NWs) have attracted much attention for the fabrication of novel nanostructured devices. In this paper, the influence of an AlN seeding layer on the nucleation of self-assembled GaN NWs grown by plasma-assisted molecular beam epitaxy (MBE) on Si (111) substrates has been investigated. Not only is the formation of a two-dimensional compact GaN layer at the bottom of the NWs suppressed, but also a high density of vertically aligned well-separated GaN NWs originating from GaN islands are successfully obtained after introducing annealing and nitridation processes. Scanning electronic microscope and transmission electron microscope measurements show that the NWs have a high crystalline wurtzite structure nearly free of dislocations and stacking faults and the NW diameter remains constant over almost the entire length. Due to the temperature-dependent diffusion length of Ga adatoms during the nucleation process, the formation of well-separated NWs relies on the distribution and morphology of the underlying AlN seeding layer. Moreover, the SiNx layer served as mask to inhibit coalescence at the nucleation sites. The developed growth processes and the obtained results provide a viable path facilitating the use of MBE growth techniques to fabricate III-nitride NW-based materials and related devices on Si substrates. [ABSTRACT FROM AUTHOR]

Resonance effects caused by the photon–electron interaction are a focus of attention in semiconductor optoelectronics, as they are able to increase the efficiency of emission. GaN-on-silicon microdisks can provide a perfect cavity structure for such resonance to occur. Here we report GaN-based microdisks with different diameters, based on a standard blue LED wafer on a Si substrate. A confocal photoluminescence spectroscopy is performed to analyze the properties of all microdisks. Then, we systematically study the effects of radial modes and axial modes of these microdisks on photon–electron coupling efficiency by using three-dimensional finite-difference time-domain simulations. For thick microdisks, photon–electron coupling efficiency is found to greatly depend on the distributions of both the radial modes and the axial modes, and the inclined sidewalls make significant influences on the axial mode distributions. These results are important for realization of high-efficiency resonant emission in GaN-based microcavity devices. [ABSTRACT FROM AUTHOR]

Size dependence of glutathione capped CdTe quantum dots (GSH-CdTe QDs) on the sensitivity and selectivity in the fluorometric detection of ferrous (II) ions (Fe2+) has been systematically investigated. Smaller-size QDs show higher sensitivity in the detection of Fe2+, resulting in higher quenching efficiency and red shift of the fluorescence peak of QDs. Stern–Volmer plots indicate that the charge transfer model can be employed to account for the observed fluorescence quenching effect. Fe2+ is bound to the surface of QDs by GSH and excited electrons are transferred from QDs to Fe2+, which facilitates a nonradiative recombination process and a decrease in the PL efficiency. In addition, the results from time resolved photoluminescence and a confocal scanning fluorescence microscope have shown that smaller-size QDs have a faster decrease in the fluorescence lifetime compared with that of larger-size QDs with Fe2+ addition, suggesting that the fast charge transfer in smaller-size QDs should be responsible for the observed fluorescence quenching effect. This Letter provides a comprehensive understanding of the mechanism of the fluorescence for the CdTe QDs quenched by Fe2+. [ABSTRACT FROM AUTHOR]

Optical properties of c- and a-plane wurtzite-InN films with different in-plane strain are investigated by using 8 × 8 k·p method. Taking into account the influence of carrier density, the imaginary parts of ordinary and extraordinary dielectric function of c- and a-plane InN near bandedge are presented. For c-plane InN, the shift of ordinary absorption edge in the case of isotropic in-plane strain in comparison to the unstrained one is very small. For a-plane InN, the splitting between the ordinary and extraordinary components below 1 eV can be modulated with different anisotropic in-plane strain. Furthermore, the difference of splitting between the cases of in-plane strain and strain-free slightly decreases with increasing carrier concentration, which implies the influence of in-plane strain becomes weaker in higher carrier concentration. The spontaneous emission spectrum shows the ratio of peak intensity of y- and z-polarizations increases with enhancement of the splitting. It is considered that the distinct polarization dependent optical anisotropy is expected to be observed in non-polar InN film by appropriately modulating the in-plane strain. [ABSTRACT FROM AUTHOR]

The influences of Mn doping on the electrical and optical properties of the Zn1-xMnxO:N films have been investigated. Mn incorporation occupying on the Zn site has led the lattice constants and the bandgap of the films increased with the structural quality deteriorated. The electrical properties have been found to change significantly with the content of Mn in the films, due to the changes in the amount of the NO acceptors and CN compensation centers formed in the films by Mn incorporation as revealed by x-ray photoelectron spectrometry measurements. The chemical states of Mn have been identified as Mn2+ and Mn4+, corresponding to Mn occupying on the Zn site and MnO2 second phase, respectively. The conductive type and the Mn2+ content of the films show a strong effect on the magnetic properties, which can be explained from the theoretical predication on the Mn 3d and N 2p ferromagnetic (hole) coupling on the ferromagnetism. However, uncompensated spins from nonuniform distribution of Mn atoms in ZnO may also be responsible for the observation of ferromagnetism signature at least on the high resistant samples. [ABSTRACT FROM AUTHOR]

The influence of anisotropic strain on the valence band structure and related properties, including excitonic transition energies, transition polarization selection rules, band-edge hole effective masses, and exciton reduced effective masses, of polar and nonpolar plane GaN are systematically investigated using the well-known k·p Hamiltonian approach. We re-examine the band deformation potentials D3 and D4, and interband hydrostatic deformation potentials a1 and a2, and find that they take the values 9.4, -4.7, -3.0, and -12.4 eV, respectively. In order to correctly interpret the optical properties of GaN, the spin-orbit coupling effect cannot be neglected. Our numerical calculations show that pure linear polarization light emissions and absorptions can be obtained. In addition, the two topmost valence subbands can be effectively separated to reduce the band-edge density of state by manipulating the strain states in GaN epilayers, which is favorable for laser diode design. Furthermore, the band-edge hole effective masses exhibit significant in-plane anisotropy and are sensitive to the residual strain, while the influence of the residual strain on the exciton reduced effective masses is relatively weak. [ABSTRACT FROM AUTHOR]

The evolution of optical and electrical properties induced by rapid thermal annealing is studied on nitrogen-doped ZnO samples grown by metal-organic chemical vapor deposition (MOCVD). Correspondingly, in the Raman spectra carbon cluster related D and G modes have been observed to increase with annealing temperature. The increase in the intensity ratio of D and G modes indicates growing of carbon clusters, revealing an interesting change in unintentional doped carbon, which is a popular impurity in MOCVD grown N-doped ZnO. Substitutional or interstitial carbons in the grains may migrate to grain boundaries to incorporate with some existing carbon clusters to form larger ones. Accordingly, zinc vacancies will then be easily formed as annealing temperature increased, resulting in eminent green band emission at room temperature photoluminescence. The band edge emissions also show significant changes with several shoulders observed by thermal annealing, which can be ascribed to acceptor or donor related emissions. The changes in emissions agree well with the evolution of the electrical property of annealed samples. This study shows that unintentional doped carbon has a great influence on ZnO growth by forming clusters in the grain boundary area and also on the optical and electrical properties by forming C related defects in the grains. [ABSTRACT FROM AUTHOR]

Monitoring and reducing NO 2 pollution at room temperature is indispensable for human survival. Thus, we propose a light-activated route (UV light, 100 mW/cm2) to realize a high-performance NO 2 detection based on CuO/rGO gas sensor. The CuO/rGO sensor under UV light illumination exhibits a high response of 22.18–100 ppm NO 2 at 23 ℃, which is approximately 1.36 times of the CuO/rGO sensor and 2.31 times of the CuO sensor under dark, respectively. Meanwhile, under UV light illumination, the CuO/rGO sensor has a fast response/recovery speed of 10.9/30.9 s to 20 ppm NO 2 at 23 ℃, which is obviously better than that under dark. Moreover, the light-activated CuO/rGO sensor has excellent repeatability, selectivity, ultra-low detection limit (50 ppb) and long-term stability. The significantly appealing gas-sensing performance of CuO/rGO sensor is mainly ascribed to the mesoporous structure, high specific surface area and plentiful oxygen vacancy of CuO/rGO nanocomposites. More attractively, the photo-generated carriers and formed heterojunction also greatly improve the carrier migration in the context of the NO 2 /CuO/rGO interaction, enhancing the gas-sensing performance of gas sensor. Our work will provide insight in utilizing light illumination to realize ultrasensitive and room-temperature detection of ppb-level NO 2 gas. • UV-activated CuO/rGO heterojunctions for fast and ppb-level NO 2 gas sensing at room temperature are demonstrated. • CuO/rGO-L sensor possesses a fast response/recovery speed and high response at room temperature. • After 30 days, CuO/rGO-L sensor still maintains stable and high performance at room temperature. • The sensing mechanism of CuO/rGO sensor under UV light illumination to trace NO 2 gas is deduced in detail. [ABSTRACT FROM AUTHOR]

We report the interaction between different sizes of CdTe quantum dots (CdTe QDs) and copper (II) ion (Cu2+) via experimental and theoretical aspects. Different sizes of CdTe QDs are synthesized and size effects on the selectivity in the detection of Cu2+ ions are studied. Experimental results indicate that with the size of CdTe QDs from 1.8 nm to 2.7 nm and to 3.2 nm increases, the linear range gets wider. For the smallest size of QD (QD 524 , 1.8 nm), the linear range is 1.0–5.0 × 10−5 M with a limited detection of 2.8 × 10−5 M. The Stern–Volmer plots at different temperatures demonstrate that the fluorescence of CdTe QDs is quenched by Cu2+ ion through a dynamic quenching mechanism, and the physiological mechanism is analyzed. Electrons are transferred from CdTe QDs to Cu2+ ion, and Cu2+ ion acquire electrons and are reduced to Cu+ ion, leading to fluorescence quenching. Meanwhile, with the increase in the number of transferred electrons, the phenomenon of fluorescence quenching is more obvious. In order to validate the process of electron transfer, the amount of transferred charge between Cu2+ and CdTe QDs are calculated by using first principles density functional theory (DFT). Calculation results show that the smaller the QDs are, the more electrons they transfer. The linear range of the smaller size QDs (QD 524) is the narrowest, indicating fluorescence quenching is indeed the most obvious of all three sizes. • Size effects of CdTe QDs on the sensitivity and selectivity in the fluorometric detection of Cu2+ ion are studied. • The process of electron transfer between CdTe QDs and Cu2+ ion is validated by first-principles calculation. • The smaller sized CdTe QDs owns the larger number of transferred electrons, resulting in lower PL efficiency. [ABSTRACT FROM AUTHOR]

In this paper, carrier transport and gain mechanisms are exploited in the $\beta $ -Ga2O3-based metal–semiconductor–metal photodetectors with Au back-to-back Schottky contacts. The resultant devices exhibit a low dark current of <10 pA at 10 V, a sustaining bias over 500 V without electric breakdown, a self-powered sensitivity with a UVC-to-visible rejection ratio over $10^{{3}}$ , and a photo-to-dark current ratio of 50 at 473 K, indicative of its strong operation capability at high temperature and in harsh environments. Temperature-dependent current–voltage features reveal that the dark reverse leakage is dominated by the thermionic field emission at low electric field and Poole–Frenkel emission from a deep trap level of 0.42 eV under the conduction band at high field, respectively. These negatively charged traps positioned below the Fermi level in the vicinity of Schottky interface capture photogenerated holes and reduce the barrier height upon illumination. The temperature- and bias-dependent photoresponse features are identified in physics that the photoconductive gain as well as slow response speed is originated from the change of barrier height due to trap repopulation. [ABSTRACT FROM AUTHOR]

We have successfully obtained a hexagonal single crystal GaN layer with (002) orientation by nitridating β-Ga2O3 film under NH3 flow despite structural mismatch between β-Ga2O3 and hexagonal GaN. The conversion process of β-Ga2O3 to GaN has also been systematically investigated. The nitridated GaN layer shows a network structure without significant stress, which makes it very suitable to be used as a template for the epitaxial growth of high-quality GaN films. The GaN/Ga2O3 heterostructure can also be used to obtain free-standing GaN (FS-GaN) films by self-separation or chemical lift-off (CLO) process due to the selective etching of β-Ga2O3. Further investigation demonstrates the feasibility of the in situ growth of low-stress FS-GaN substrates by halide vapor phase epitaxy (HVPE). [ABSTRACT FROM AUTHOR]

Abstract We report here the preparation of porous single-crystal GaN films by direct top-down high temperature nitridation of β-Ga 2 O 3. It is found that, although the crystallographic orientations of the original β-Ga 2 O 3 samples are different, the GaN films converted from both bulk (200) β-Ga 2 O 3 single crystal and (−201) β-Ga 2 O 3 film have the same (0002) orientation and show no obvious stress. And we also found that the crystal quality of converted GaN strongly depends on the crystal quality of β-Ga 2 O 3. In particular, we have successfully converted β-Ga 2 O 3 film entirely to single-crystal GaN porous film on sapphire, and the self-separation happens naturally between the porous GaN film and sapphire. Highlights • Single-crystal GaN porous layers have been obtained by the nitridation of β-Ga 2 O 3. • The crystal quality of converted GaN strongly depends on the quality of β-Ga 2 O 3. • Self-separation happens naturally between the porous GaN layer and sapphire. [ABSTRACT FROM AUTHOR]