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AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMT) with a low-temperature epitaxy (LTE)-grown single crystalline AlN gate dielectric were demonstrated for the first time and the post-gate annealing effects at 400 &deg, C were studied. The as-deposited LTE-AlN MISHEMT showed a maximum drain current (IDmax) of 708 mA/mm at a gate bias of 4 V and a maximum extrinsic transconductance (gmmax) of 129 mS/mm. The 400 &deg, C annealed MISHEMT exhibited an increase of 15% in gmmax, an order of magnitude reduction in reverse gate leakage and about a 3% suppression of drain current (ID) collapse. The increase of gmmax by post-gate annealing is consistent with the increase of 2DEG mobility. The suppression of ID collapse and the reduction of gate leakage current is attributed to the reduction of interface state density (5.0 &times, 1011 cm&minus, 2eV&minus, 1) between the AlN/GaN interface after post-gate annealing at 400 &deg, C. This study demonstrates that LTE grown AlN is a promising alternate material as gate dielectric for GaN-based MISHEMT application.

Low leakage current Schottky barrier diodes (SBDs) were fabricated on $\mathbf{30}\ \mu\mathbf{m}$ thick Mg-compensated GaN drift layer (DL) grown on a free-standing GaN substrate and tested up to 5.48 MeV $\alpha$ -particle energy. The Mg-compensated $\mathbf{30}\ \mu\mathbf{m}$ thick n--GaN DL was grown by MOCVD with low charge carrier density (CCD) of $\mathbf{4.1}\times \mathbf{10}^{\mathbf{15}}/\mathbf{cm}^{\mathbf{3}}$ . The observation of low CCD in the GaN DL by Mg-compensation helps to reduce the reverse leakage current (I R ) of SBDs to 2 pA and in the formation of $\mathbf{30}\mu\mathbf{m}$ depletion width (DW) even at 0 V. The fabricated GaN SBDs detected $\alpha$ -particle up to energy of 5.48 MeV with high charge collection efficiencies (CCE) of 100% emitted from 241 Am source.

The interface trap behavior in SiNx/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) and Schottky HEMTs on CVD diamond was studied using parallel conductance techniques. In MISHEMTs, two different types of traps were identified, fast with the time constant $\tau_{\mathbf{T}}\equiv(\mathbf{0.1}-\mathbf{3.6})\mu\mathbf{s}$ and slow with $\tau_{\mathbf{T}}\equiv\mathbf{6}$ ms whereas, only fast traps were obtained in conventional HEMTs. These fast traps could be related to AlGaN/GaN hetero-interface which are identical in both the devices. The density of fast trap $(\pmb{D}_{\mathbf{TT}})$ is almost similar for MIS-HEMTs and HEMTs (∼of $\mathbf{0.7}-\mathbf{8\ x\ 10}^{\mathbf{11}}\mathbf{cm}^{-\mathbf{2}}\mathbf{eV}^{-\mathbf{1}})$ . The density of slow trap $(\pmb{D}_{\mathbf{Ts}})$ in MIS-HEMTs was estimated as $\sim\mathbf{6}-\mathbf{11\ x\ 10}^{\mathbf{12}}\mathbf{cm}^{-\mathbf{2}}\mathbf{eV}^{-\mathbf{1}}$ which could be related to the Schottky/dielectric interface.

Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of GaN as an α-particle detector. Work in developing GaN-based radiation sensors are still evolving and GaN sensors have successfully detected α-particles, neutrons, ultraviolet rays, x-rays, electrons and γ-rays. This review elaborates on the design of a good radiation detector along with the state-of-the-art α-particle detectors using GaN. Successful improvement in the growth of GaN drift layers (DL) with 2 order of magnitude lower in charge carrier density (CCD) (7.6 × 1014/cm3) on low threading dislocation density (3.1 × 106/cm2) hydride vapor phase epitaxy (HVPE) grown free-standing GaN substrate, which helped ~3 orders of magnitude lower reverse leakage current (IR) with 3-times increase of reverse breakdown voltages. The highest reverse breakdown voltage of −2400 V was also realized from Schottky barrier diodes (SBDs) on a free-standing GaN substrate with 30 μm DL. The formation of thick depletion width (DW) with low CCD resulted in improving high-energy (5.48 MeV) α-particle detection with the charge collection efficiency (CCE) of 62% even at lower bias voltages (−20 V). The detectors also detected 5.48 MeV α-particle with CCE of 100% from SBDs with 30-μm DL at −750 V.

A low voltage (&minus, 20 V) operating high-energy (5.48 MeV) &alpha, particle detector with a high charge collection efficiency (CCE) of approximately 65% was observed from the compensated (7.7 &times, 1014 /cm3) metalorganic vapor phase epitaxy (MOVPE) grown 15 &micro, m thick drift layer gallium nitride (GaN) Schottky diodes on free-standing n+-GaN substrate. The observed CCE was 30% higher than the bulk GaN (400 &micro, m)-based Schottky barrier diodes (SBD) at &minus, 20 V. This is the first report of &alpha, &ndash, particle detection at 5.48 MeV with a high CCE at &minus, 20 V operation. In addition, the detectors also exhibited a three-times smaller variation in CCE (0.12 %/V) with a change in bias conditions from &minus, 120 V to &minus, 20 V. The dramatic reduction in CCE variation with voltage and improved CCE was a result of the reduced charge carrier density (CCD) due to the compensation by Mg in the grown drift layer (DL), which resulted in the increased depletion width (DW) of the fabricated GaN SBDs. The SBDs also reached a CCE of approximately 96.7% at &minus, 300 V.

We have investigated the self-heating effect on DC and RF performances of identically fabricated AlGaN/GaN HEMTs on CVD-Diamond (GaN/Dia) and Si (GaN/Si) substrates. Self-heating induced device performances were extracted at different values drain bias voltage ( $V_{D}$ ) and dissipated DC power density ( $P_{D}$ ) in continuous wave (CW) operating condition. The effect of self-heating was observed much lesser in GaN/Dia HEMTs than GaN/Si HEMTs in terms of $I_{\mathrm{D}}$ , $I_{\mathrm{G}}$ , $g_{\mathrm{m}}$ , $f_{\mathrm{T}}$ and $f_{\mathrm{max}}$ reduction. Increased channel temperature caused by joule heating at high $P_{\mathrm{D}}$ reduces the 2-DEG carrier mobility in the channel of the device. This behaviour was also confirmed by TCAD simulation which showed ~3.9-times lower rising rate of maximum channel temperature and lowers thermal resistance ( $R_{\mathrm{th}}$ ) in GaN/Dia HEMTs than GaN/Si HEMTs. Small signal measurements and equivalent circuit parameter extraction were done to analyze the variation in performance of the devices. Our investigation reveals that the GaN/Dia HEMT is a promising candidate for high power density CW operation without significant reduction in electrical performance in a large drain bias range.

AlGaN/GaN metal-insulator-semiconductor (MIS) diodes were fabricated using low temperature epitaxy (LTE) grown AlN at 200 °C, a technique combining both physical vapor deposition and chemical vapor deposition. The interface trap characteristics of the MIS-diodes were investigated using the frequency dependent parallel conductance method. Two distinct interface trapping regions were observed, where the fast interface traps had an estimated density (Dit) as low as 6.7 × 1011 cm−2 eV−1 while the slow interface traps Dit were as low as 6.8 × 1011 cm−2 eV−1. About 3.8 × improvement in Dit was achieved compared to our previous work by optimization of the LTE deposition conditions. The fast traps are located within the energy interval of 0.24–0.30 eV below the conduction band while the slow traps are located 0.44–0.56 eV below the conduction band. The observed fast traps were associated with the AlGaN/GaN interface, while the observed slow traps may have formed at AlN/GaN interface during the deposition of AlN by LTE.

Current-voltage-temperature characteristics (0oC to 150oC) of SBDs on highly compensated 15µm and 30µm n-type GaN drift layer were measured for voltages up to -300V and up to -800V, respectively. When the temperature is between 75oC and 100oC, both SBDs exhibited a similar change in conduction mechanism from thermionic field emission (TFE) to thermionic emission (TE) due to the activation of N-vacancies (VN) (Ea=-1.67eV). However, at high voltages when the temperature is >100oC, the conduction mechanism changes from TE to TFE due to the de-trapping of electrons from the activated carbon-traps (Ea=+0.69eV) in the grown DLs.

Vertical Schottky barrier diodes (SBD) with different drift-layer thicknesses (DLT) of GaN up to 30 μm grown by metalorganic chemical vapour deposition (MOCVD) were fabricated on free-standing GaN grown by hydride vapour phase epitaxy (HVPE). At room temperature, SBD’s exhibited average barrier heights (ΦB) in the range of 0.73 eV to 0.81 eV. The effective barrier heights (ΦBeff) of SBDs with different DLT also exhibited a similar range of ΦB measured at room temperature. The measured reverse breakdown voltages (VBD) of SBDs increased from 562 V to 2400 V with an increase in DLT. The observation of high VBD of SBDs could be due to the lower effective donor concentration (7.6×1014 /cm3), which was measured from SIMS analysis. The measured VBD of 2400 V is the highest value ever reported for a 30 μm DLT vertical GaN SBD without additional edge termination or field plate (FP). Published version

We fabricated a fiber laser that uses a thin semiconductor layer surrounding the glass core as the gain medium. This is a completely new type of laser. The In2Te3 semiconductor layer is about 15-nm thick. The fiber laser has a core diameter of 14.2 μm, an outside diameter of 126 μm, and it is 25-mm long. The laser mirrors consist of a thick vacuum-deposited aluminum layer at one end and a thin semitransparent aluminum layer deposited at the other end of the fiber. The laser is pumped from the side with either light from a halogen tungsten incandescent lamp or a blue light emitting diode flash light. Both the In2Te3 gain medium and the aluminum mirrors have a wide bandwidth. Therefore, the output spectrum consists of a pedestal from a wavelength of about 454 to 623 nm with several peaks. There is a main peak at 545 nm. The main peak has an amplitude of 16.5 dB above the noise level of −73 dB.