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In this paper, we report an analysis of reverse current mechanisms observed in GaN Schottky barrier diodes leading to hysteretic behavior of the I–V curves at low temperature. By means of DC measurements from 33 to 475 K, we demonstrate the presence of two leakage mechanisms when comparing the experiments with the results obtained using a unified model to predict the ideal reverse current of the diode. Poole–Frenkel emission is the dominant mechanism for temperatures above 200 K, while trap-assisted tunneling prevails for lower temperatures, where also, hysteresis cycles are revealed by means of DC dual-sweep voltage measurements. The energy of the corresponding traps has also been determined, being around 0.2 and 0.45 eV, respectively. The hysteresis phenomenon is attributed to the bias-induced occupancy of the energy states originating the leakage-current processes, which leads to the reduction of the reverse current after a high negative voltage is applied to the diode. [ABSTRACT FROM AUTHOR]

We have analyzed and modeled the reverse-biased gate leakage current in a Schottky-gate AlGaN/GaN high electron mobility transistor. While the Poole–Frenkel emission current along conductive threading dislocations dominates at low negative gate bias, the trap-assisted tunneling of thermally energized electrons and the thermal emission of electrons from threading dislocations aided by dislocation-related states at multiple energy levels within the AlGaN bandgap are dominant at moderate to large reverse bias. Additionally, deep trap levels of high density localized near the gate/AlGaN interface cause significant leakage at 473 K at low to moderate reverse bias, which could be specific to the device we have analyzed. We extracted about 10 12 cm − 2 traps near the AlGaN/GaN interface from the difference of the barrier layer electric field profile obtained from the experimental high-frequency capacitance–gate voltage and the one needed for final matching. The thermionic- and the thermionic field-emission currents are considerably low; the latter, however, dominates in the defect-free case. Finally, the simulation framework we developed here helped us identify various conduction mechanisms contributing to the reverse-biased gate leakage and the density and electronic structure of the responsible defects. [ABSTRACT FROM AUTHOR]

Strain plays an important role in the performance and reliability of AlGaN/GaN high electron mobility transistors (HEMTs). However, the impact of strain on the performance of proton irradiated GaN HEMTs is yet unknown. In this study, we investigated the effects of strain relaxation on the properties of proton irradiated AlGaN/GaN HEMTs. Controlled strain relief is achieved locally using the substrate micro-trench technique. The strain relieved devices experienced a relatively smaller increase of strain after 5 MeV proton irradiation at a fluence of 5 × 1014 cm−2 compared to the non-strain relieved devices, i.e., the pristine devices. After proton irradiation, both pristine and strain relieved devices demonstrate a reduction of drain saturation current (Ids,sat), maximum transconductance (Gm), carrier density (ns), and mobility (μn). Depending on the bias conditions the pristine devices exhibit up to 32% reduction of Ids,sat, 38% reduction of Gm, 15% reduction of ns, and 48% reduction of μn values. In contrast, the strain relieved devices show only up to 13% reduction of Ids,sat, 11% reduction of Gm, 9% reduction of ns, and 30% reduction of μn values. In addition, the locally strain relieved devices show smaller positive shift of threshold voltage compared to the pristine devices after proton irradiation. The less detrimental impact of proton irradiation on the transport properties of strain relieved devices could be attributed to reduced point defect density producing lower trap center densities, and evolution of lower operation related stresses due to lower initial residual strain. [ABSTRACT FROM AUTHOR]

This work demonstrates a high-performance monolithically integrated GaN inverters platform, which incorporates enhancement-mode (E-mode) and depletion-mode (D-mode) GaN high-electron-mobility transistors (HEMTs) simultaneously using an Al:HfOx-based charge trapping layer. The developed E-mode HEMT exhibits a positive threshold voltage of 2.6 V, a high ON–OFF current ratio of 1.9 × 108, a current density of 376 mA/mm, and an ON-resistance of 15.31 Ω·mm. Moreover, the direct-coupled field-effect-transistor logic (DCFL) GaN inverter was characterized with and without D-mode device threshold voltage (VTH) modulation, demonstrating improved output swing and switching threshold shift by proposed VTH modulation. The optimized DCFL GaN inverter manifests a switching threshold of 2.34 V, a logic voltage output swing of 4.98 V, and substantial logic-low and logic-high noise margins of 2.16 and 2.49 V, respectively, at a supply voltage of 5 V. These results present a promising approach toward realizing monolithically integrated GaN logic circuits for power IC applications. [ABSTRACT FROM AUTHOR]

The factors limiting channel mobility in AlSiO/p‐type GaN metal–oxide–semiconductor (MOS) field‐effect transistors are examined by performing Hall‐effect measurements in conjunction with a gate bias, with and without a thin AlN interlayer. In the absence of this interlayer, the free carrier concentration associated with the Hall effect is significantly reduced compared with the net gate charge density estimated from capacitance–voltage data, indicating that electrons are trapped to a significant extent at the MOS interface. These interface traps are found to have an energy ≈20 meV above the Fermi level in strong inversion based on temperature‐dependent Hall effect data. The insertion of a 0.8 nm‐thick AlN interlayer eliminates charge trapping such that almost all gate charges are mobile. The mobility components could be divided into types based on their effect on the effective electric field perpendicular to the channel. Coulomb scattering centers resulting from interface states are evidently reduced by inserting the AlN interlayer, which also enhances the channel mobility to over 150 cm2 V−1s−1. [ABSTRACT FROM AUTHOR]

The aim of this article is to show that it is possible to rapidly estimate the activation energies of electron traps in AlInN/GaN transistors operating at room temperature by combining pulsed electrical measurements with photoionization techniques using infrared illumination. This technique avoids the time‐consuming task of performing electrical measurements at different temperatures to determine the activation energies of the electron traps using Arrhenius laws. Thus, a deep level at 1.3 eV is detected and attributed to the presence of carbon in GaN buffer of the component. Moreover, we have highlighted that the trapping effect can be screened when the transistors are biased with a high drain‐source voltage during pulsed measurements. [ABSTRACT FROM AUTHOR]

In this paper, the degradation behaviors of the ferroelectric gate Gallium nitride (GaN) high electron mobility transistor (HEMT) under positive gate bias stress are discussed. Devices with a gate dielectric that consists of pure Pb(Zr,Ti)O3 (PZT) and a composite PZT/Al2O3 bilayer are studied. Two different mechanisms, charge trapping and generation of traps, both contribute to the degradation. We have observed positive threshold voltage shift in both kinds of devices under positive gate bias stress. In the devices with a PZT gate oxide, we have found the degradation is owing to electron trapping in pre-existing oxide traps. However, the degradation is caused by electron trapping in pre-existing oxide traps and the generation of traps for the devices with a composite PZT/Al2O3 gate oxide. Owing to the large difference in dielectric constants between PZT and Al2O3, the strong electric field in the Al2O3 interlayer makes PZT/Al2O3 GaN HEMT easier to degrade. In addition, the ferroelectricity in PZT enhances the electric field in Al2O3 interlayer and leads to more severe degradation. According to this study, it is worth noting that the reliability problem of the ferroelectric gate GaN HEMT may be more severe than the conventional metal–insulator–semiconductor HEMT (MIS-HEMT). [ABSTRACT FROM AUTHOR]

Kink effect is observed in Al 0.83 In 0.17 N/GaN high electron mobility transistor by measuring I D -V D S characteristics at a low sweep rate. It is inferred that the kink is induced due to the trapping/detrapping of charge carriers at deep levels present in the GaN buffer in the gate–drain access region. The detrapping of charge carriers from the deep levels is by the hot-electron-assisted mechanism. Two types of traps with activation energies, 0.29 eV (donor-like) and 0.57 eV (acceptor-like) were extracted by temperature-dependent transient drain current analysis. It is concluded that the deep-acceptor-like trap with a large emission time constant is responsible for the kink effect. [ABSTRACT FROM AUTHOR]

GaN‐based materials are the hottest research topic in UV photodetectors (PDs) because of their low operating voltage, small volume, long lifetime, high‐temperature resistance, and low energy consumption. However, there are still fundamental issues to be overcome, and the most important issue is to get a photoconductive gain. In this paper, the following new approaches are provided to innovatively improve the photoconductive gain of UV PDs in GaN‐based materials. First, the aspect ratio of the 1D GaN microwire (MW) structure is dramatically improved by analyzing the pulse growth mechanism using the metal‐organic vapor deposition system. Second, the comprehensive strain behavior in the MW epitaxial growth system is successfully analyzed. Third, the fabricated metal‐semiconductor‐metal‐based MW UV PD shows photoresponsivity and sensitivity of 28.365 A W−1 and 93.16%, respectively, at the −2 V bias, which significantly outperforms the conventional structures in the UV region. Finally, a trap‐assisted Poole–Frenkel effect‐based energy bandgap mechanism, that allows the defect level formed by lattice mismatch between the substrate and GaN to be used as an electron carrier path, is newly defined. This study will present the direction of future UV PDs by providing a new MW structure based on GaN materials, a third‐generation semiconductor. [ABSTRACT FROM AUTHOR]

A detailed study comparing defect incorporation between laser-assisted metal-organic chemical vapor deposition (MOCVD)-grown GaN and conventional low- and high-growth-rate MOCVD GaN was conducted. Using deep-level transient and optical spectroscopy, traps throughout the bandgap were characterized where traps were found at EC-0.25 eV, EC-0.57 eV, EC-0.72 eV, EC-0.9 eV, EC-1.35 eV, EC-2.6 eV, and EC-3.28 eV in all three samples. This indicates no new traps were observed in the laser-assisted MOCVD GaN sample. Overall, the trap concentrations in the laser-assisted MOCVD sample were ∼2× higher than the optimal low-growth-rate sample, but this is primarily due to the increase in gallium vacancy EC-2.6 eV and carbon-related EC-3.28 eV trap concentrations. The EC-0.9 eV trap concentration was ∼2× higher in the laser-assisted sample, so proton irradiation experiments were conducted to identify the physical source of this level. The results indicated this was a native point defect likely related to gallium interstitials. Overall, this study shows that the laser-assisted MOCVD growth method is promising for future thick, high-quality GaN epilayers after further growth optimizations. [ABSTRACT FROM AUTHOR]

The characteristics of an AlGaN/GaN high-electron-mobility transistor buffer structure are studied and optimized by employing an AlN/GaN superlattice (SL) structure. Through vertical leakage analysis and back-gate measurement, combined with Silvaco-TCAD simulation, the influence of buffer trapson the carrier transport behaviors and electrical performance for SL buffer structures under a high electric field is analyzed. The AlN/GaN SL buffer structures are further optimized with various AlN/GaN thickness ratios and their total thickness through both simulation and experimental studies. As a result, a high breakdown voltage of up to 1.3 kV with a maximum breakdown electric field of 2.8 MV cm−1 has been achieved. Moreover, the buffer trapping effect is dramatically suppressed, leading to a minimum drop of channel current for the optimized sample, in which donor traps are found to play a positive role in the device dynamic characteristics. [ABSTRACT FROM AUTHOR]

Multichannel high electron mobility transistor (MC-HEMT) heterostructures are one of the choices for improved power performance of GaN HEMTs. By comparing the experimentally obtained two-dimensional electron gas (2DEG) concentration of unintentionally doped (UID) AlGaN/GaN MC-HEMTs with simulated 2DEG concentration, we hypothesized that hole trap(s) exist at the buried GaN/AlGaN interfaces, which act as sources of 2DEG in UID MC-HEMT heterostructures. Furthermore, these hole traps stop the Fermi level from cutting the valence band at GaN/AlGaN interfaces, which in turn precludes the generation of parallel two-dimensional hole gas (2DHG) in the MC-HEMT. However, no experimental report is present as a proof for the existence of such a hole trap in MC-HEMT heterostructures. In this study, a capacitance–conductance method on single and dual channel HEMTs revealed traps with higher time constant of 19–28.7 μs exclusively for the dual channel HEMT heterostructure. These traps are observed at the buried GaN/AlGaN interface of the dual channel HEMT; hence, they are attributed to possible hole traps at this interface. By conducting systematic deep level transient spectroscopy measurements, the existence of hole traps is confirmed at the buried GaN/AlGaN interface with an activation energy of 717 meV and a capture cross section of 1.3 × 10−14 cm2. This experimental evidence of the existence of hole traps at the GaN channel/AlGaN interface further supports our claim that these hole traps act as the source of 2DEG in UID MC-HEMTs and that buried parallel 2DHG channels do not exist in MC-HEMTs. [ABSTRACT FROM AUTHOR]

In this work, the effects of proton-induced trap evolution on the electrical performances of AlGaN/GaN metal–insulator–semiconductor (MIS) high-electron-mobility-transistors (HEMTs) have been investigated in detail. Contrary to observed proton-induced degradation in sheet electron density (ns), carrier mobility (μn), and sheet resistance (RSH), a significant improvement in gate leakage current (IG) and off-state drain–source breakdown voltage (BVDS) is found in irradiated devices. The low-frequency noise (LFN) results show that the density of traps in the AlGaN layer and AlGaN/GaN interface increases after irradiation, which leads to a degradation in ns, μn, and RSH and an improvement in BVDS due to enhanced electron trapping and depletion. Furthermore, the measurement results obtained from the frequency-dependent conductance technique show that irradiated devices exhibit decreased trap density (DT) at the insulator/semiconductor interface with hardly changed trap energy level (ET), which confirms the observed proton-induced decrease in IG. An increase in DT at the AlGaN/GaN interface is also found after irradiation, which is consistent with LFN results. These traps with deeper ET induce a serious Coulomb scattering effect. This work provides valuable information for the systematic understanding of the proton irradiation effect of AlGaN/GaN MIS-HEMTs. [ABSTRACT FROM AUTHOR]

In this Letter, threshold voltage instability of p-GaN gate AlGaN/GaN HEMTs under high-temperature reverse bias (HTRB) stress has been investigated in detail. The experimental results show that the threshold voltage increases by 0.62 V after 100 ks stress at 200 °C. Especially, the degradation phenomenon is unrecoverable. A deep-level transient spectroscopy (DLTS) technique is used to characterize the defect evolution process during the stress. Two kinds of electron traps within the p-GaN layer were proposed to explain the degradation, which were generated by the injected high-energy electrons from the gate electrode. One is referred to as fixed charge trap, and another is trap E3 (EC-0.7 eV). With the aid of high temperature, more electrons are injected and trapped in the fixed charge trap, which causes the permanent threshold voltage increase. In addition, the concentration and capture cross section of trap E3 were extracted as well, which are considered to dominate the recoverable degradation of the device due to the relatively shallower energy level. [ABSTRACT FROM AUTHOR]

Herein, the performance of AlGaN/GaN high-electron-mobility transistor (HEMT) devices fabricated on Si and sapphire substrates is investigated. The drain current of the AlGaN/GaN HEMT fabricated on sapphire and Si substrates improved from 155 and 150 mA/mm to 290 and 232 mA/mm, respectively, at VGS = 0 V after SiO2 passivation. This could be owing to the improvement in the two-dimensional electron gas charge and reduction in electron injection into the surface traps. The SiO2 passivation resulted in the augmentation of breakdown voltage from 245 and 415 V to 400 and 425 V for the AlGaN/GaN HEMTs fabricated on Si and sapphire substrates, respectively, implying the effectiveness of SiO2 passivation. The lower transconductance of the AlGaN/GaN HEMT fabricated on the Si substrate can be ascribed to the higher self-heating effect in Si. The X-ray rocking curve measurements demonstrated that the AlGaN/GaN heterostructures grown on sapphire exhibited a full-width half maximum of 368 arcsec against 703 arcsec for the one grown on Si substrate, implying a better crystalline quality of the AlGaN/GaN heterostructure grown on sapphire. The AlGaN/GaN HEMT fabricated on the sapphire substrate exhibited better performance characteristics than that on the Si substrate, owing to the high crystalline quality and improved surface. [ABSTRACT FROM AUTHOR]

Many kinds of defects are present in AlGaN/GaN-on-Si based power electronics devices. Their identification is the first step to understand and improve device performance. Electron traps are investigated in AlGaN/GaN-on-Si power diodes using deep level transient Fourier spectroscopy (DLTFS) at different bias conditions for two Schottky contact's etching recipes. This study reveals seven different traps corresponding to point defects. Their energy level ET ranged from 0.4 eV to 0.57 eV below the conduction band. Among them, two new traps are reported and are etching-related: D3 (ET = 0.47–0.48 eV; σ ≈ 10−15 cm2) and D7 (ET = 0.57 eV; σ = 4.45 × 10−12 cm2). The possible origin of the other traps are discussed with respect to the GaN literature. They are proposed to be related to carbon and nitrogen vacancies or to carbon, such as CN-CGa. Some others are likely due to crystal surface recombination, native defects or a related complex, or to the nitrogen antisite: NGa. [ABSTRACT FROM AUTHOR]

Production rate (PR = trap concentration/incident fluence) of traps formed by energetic particles is important for predicting device degradation caused by radiation when developing radiation-resistant devices. We demonstrate a clear correlation between non-ionizing energy loss (NIEL) and PR of an electron trap at about 0.12–0.20 eV below the conduction band edge [EC − (0.12–0.20) eV] for various types of energetic particles in gallium nitride (GaN). NIEL values in GaN for electrons, protons, and α -rays were calculated using a screened-relativistic treatment, and NIEL values for gamma-rays were calculated by simulating slowed-down spectra due to shielding material. To obtain the PRs of the electron trap, 60Co gamma-rays with an average photon energy of 1.25 MeV and electron beams with energies from 137 keV to 2 MeV were irradiated onto n-type GaN Schottky barrier diodes. We measured the concentration of an electron trap at EC − (0.13–0.14) eV using deep-level transient spectroscopy. We also used the PRs of electron traps with similar energy levels of EC − (0.12–0.20) eV from previous studies on electrons, protons, and α -rays irradiated on GaN. All the trap PRs were proportional to the NIEL in a range of eight orders of magnitude, which confirms that the energy levels formed by various energetic particles have the same origin of being generated by atomic displacements. The obtained relationship coefficient between the NIEL and PRs of the trap is useful for predicting the degradation of GaN-based devices due to traps formed by various kinds of radiation. [ABSTRACT FROM AUTHOR]

We report on the fabrication and electrical characterization of AlGaN/GaN normally off transistors on silicon designed for high-voltage operation. The normally off configuration was achieved with a p-gallium nitride (p-GaN) cap layer below the gate, enabling a positive threshold voltage higher than +1 V. The buffer structure was based on AlN/GaN superlattices (SLs), delivering a vertical breakdown voltage close to 1.5 kV with a low leakage current all the way to 1200 V. With the grounded substrate, the hard breakdown voltage transistors at VGS = 0 V is 1.45 kV, corresponding to an outstanding average vertical breakdown field higher than 2.4 MV/cm. High-voltage characterizations revealed a state-of-the-art combination of breakdown voltage at VGS = 0 V together with low buffer electron trapping effects up to 1.4 kV, as assessed by means of substrate ramp measurements. [ABSTRACT FROM AUTHOR]

Electron traps in AlGaN/GaN high electron mobility transistors were studied by combining theoretical and experimental methods. Energy levels about EC-0.9 eV due to irradiation are identified by deep-level transient spectroscopy (DLTS). Two electron traps, H1 (EC-0.63 eV) and H2 (EC-0.9 eV), were observed in the DLTS spectra. H1 was produced in device or material manufacturing, and H2 was caused by displacement damage. First, we reported that the signal peak of H2 can contribute from three defects labeled H2-1, H2-2, and H2-3 with energies EC-0.77 eV, EC-0.9 eV, and EC-0.98 eV, respectively. According to defect migration temperature and first principles calculation results, it is found that different configurations of di-nitrogen vacancy structures are the source of EC-0.77 eV and EC-0.9 eV signals. The defect of EC-0.98 eV is more stable at high temperatures, which may be related to gallium vacancy. [ABSTRACT FROM AUTHOR]

A 3-MeV proton irradiation experiment was carried out on an AlGaN/GaN high-electron-mobility-transistor (HEMT). The results showed that the device's saturation drain current decreased, the threshold voltage drifted positively, and the maximum transconductance decreased after irradiation. Interestingly, the forward gate leakage current was almost unchanged, and the reverse gate leakage current was reduced by two orders of magnitude. We found that this experimental phenomenon can be well explained by the Poole–Frenkel emission model. Proton irradiation led to deeper defect energy levels and higher defect concentrations of the device. Deeper defect energy levels made it more difficult for electrons to be excited from the trap state into the conduction band. Thus, the reverse gate leakage current decreased. Higher defect concentrations led to degradation of the output and transfer curves of the device. The deep level transient spectroscopy characterization defect further proved the correctness of this model. The reduction in the reverse gate leakage current had a positive impact on AlGaN/GaN HEMT devices in high power or high frequency applications. [ABSTRACT FROM AUTHOR]

Compact modeling of charge trapping processes in GaN transistors is of fundamental importance for advanced circuit design. The goal of this article is to propose a methodology for modeling the dynamic characteristics of GaN power HEMTs in the realistic case where trapping/detrapping kinetics are described by stretched exponentials, contrary to ideal pure exponentials, thus significantly improving the state of the art. The analysis is based on: 1) an accurate methodology for describing stretched-exponential transients and extracting the related parameters and 2) a novel compact modeling approach, where the stretched exponential behavior is reproduced via multiple RC networks, whose parameters are specifically tuned based on the results of 1). The developed compact model is then used to simulate the transient performance of the HEMT devices as a function of duty cycle and frequency, thus providing insight on the impact of traps during the realistic switching operation. [ABSTRACT FROM AUTHOR]

This study investigates the recovery behavior of GaN high-electron mobility transistors on SiC substrates under different hot-carrier stress conditions. The threshold voltage shifts positively due to hot electron trapping at the buffer layer under hot-carrier stress. However, the recovery between semi-on (Vt < VG < 0 V) hot-carrier stress and on-state (VG > 0 V) carrier stress is significantly different. This phenomenon is systematically discussed in terms of the applied gate voltage under stress condition, which affects the occupation of the surface donor states. After applying a semi-on hot-carrier stress, the threshold voltage continues to shift positively after relaxing the applied voltage. In contrast, the threshold voltage exponentially recovers after applying an on-state hot-carrier stress. Silvaco technology computer aided design (TCAD) simulation was performed to verify the effect of the surface donor state on the threshold voltages. Since switching between on-state and off-state in RF-applications includes both conditions, we suggest that the surface donor states are crucial to determine the failure of devices. [ABSTRACT FROM AUTHOR]

This article analyzes the energy loss Eloss in GaN enhancement-mode (E-mode) devices under unclamped inductive switching (UIS) stresses. Based on the second-order circuit analysis and the equivalent circuit model of RS and CS in series for devices, the analytical model is developed with quantitative relationships among the Eloss, RS, and the time shift Δt between device current and voltage. The origin and physical mechanism of Eloss are revealed with the help of Technology Computer Aided Design (TCAD) simulation. The imbalance of the charges in devices due to the dynamic trapping and de-trapping of the acceptor traps is the origin of RS and Eloss. Under various configurations of energy level and density acceptor traps, the physical mechanism is discussed with simulations of electron and displacement currents. Results show that proper amount of acceptor traps at the relatively shallow energy level of ET < EV + 0.5 eV are critical to lowering the Eloss of GaN devices under UIS stresses. The calculation results using the proposed analytical model can fit well with the measurement data. This article can provide practical models and physical mechanism to analyze the device behavior and estimate the energy loss of GaN E-mode devices in the field applications under UIS stresses. [ABSTRACT FROM AUTHOR]

A double π-gate engineering technique is proposed to analyse the device performance and enhance the reliability by reducing the surface traps and buffer traps using Silvaco TCAD simulator tool. Peak electric field due to V gs , under the gate can worse the device performance and cause memory effects. The peak electric field destructs the charge carrier density (2-DEG) in the channel, lowers the charge carrier density in the channel and results in current collapse. The peak electric field make the electrons/holes (in n-type/p-type) to get energized (hot electron) and injected into buffer region and other epi-layers by the process trapping/de-trapping. Drain current collapse (∆ I dmax) and threshold voltage shift (∆V th) occur due to trapping/de-trapping. Proposed method has T-gate which is spilt into 3-pillars referred to as double-π shaped gate structure. Results obtained from the suggested technique showed that perfect peak current in the channel and uniform electric field distribution is achieved. The dc characteristics pulsed I-V, pulsed C-V, and pulsed S-parameters are analysed to study the trapping effects. • A double π-gate AlGaN/GaN HEMT is proposed with reduced surface and buffer traps. • Uniform electric field distribution is achieved with the proposed model. • Up to 400 mS of transconductance is obtained and degradation due to Kink effects are not noticed. • Buffer traps are compensated by adopting a buffer doping of 3 × e17 per cm−3. • High cut-off frequency and current gain are noticed and employed in the design of RF amplifiers. [ABSTRACT FROM AUTHOR]

In this Letter, the effects of trap states in AlN/GaN superlattice channel HEMTs (high electron mobility transistors) under total ionizing dose with γ-irradiation have been systematically investigated. After 1 Mrad γ-irradiation with a dose rate of 50 rad/s, negative drifts in threshold voltage and C–V characteristics are observed. Simultaneously, the two-dimensional electron gas sheet density of the upper channel increases from 5.09 × 1012 to 5.47 × 1012 cm−2, while that of the lower channel decreases from 4.41 × 1012 to 3.86 × 1012 cm−2, respectively. Furthermore, frequency-dependent capacitance and conductance measurements are adopted to investigate the evolution of trap states in an electron channel. The trap state density (DT = 0.21–0.88 × 1013 cm−2 eV−1) is over the ET range from 0.314 to 0.329 eV after irradiation for the upper channel, while the trap state in the lower channel decreases from 4.54 × 1011 cm−2 eV−1 at ET = 0.230 eV to 2.38 × 1011 cm−2 eV−1 at ET = 0.278 eV. The density (1.39–1.54 × 1011 cm−2 eV−1) of trap states with faster τT (0.033–0.037 μs) generated in a lower channel is located at shallower ET between 0.227 and 0.230 eV. The results reveal the mechanism of trap states in the channel, affecting the performance of HEMTs, which can provide a valuable understanding for hardening in space radiation. [ABSTRACT FROM AUTHOR]

A tunnel-oxide-free GaN-based non-volatile memory (NVM) device is proposed to untangle the trilemma among speed, retention, and endurance in the implementation of conventional NVM. The program and erase (P/E) are based on bipolar charge injection controlled by individual junction barriers, whereas the data retention relies on bipolar charge trapping in an interfacial charge storage layer. The wide bandgap energy of GaN allows the formation of deep-level traps at a dielectric/GaN interface and high junction barriers in GaN, both of which benefit long-term retention. As such, the GaN-based NVM device could get rid of the tunnel oxide, thereby enabling faster P/E processes and facilitating to decouple the enhancement of endurance from that of speed and retention. The proposed device demonstrates a P/E time of 100 ns, endurance over 106 cycles, and long retention time. [ABSTRACT FROM AUTHOR]

This work investigated deep levels in p-type GaN originating from intrinsic point defects, using deep level transient spectroscopy (DLTS) to examine homoepitaxial GaN p+–p−–n+ junction diodes grown via metalorganic vapor-phase epitaxy. Following exposure to an electron beam with an energy of 137 keV that generated nitrogen vacancies (VN) and nitrogen interstitials (NI), a peak due to EHa hole traps (at 0.52 eV) was observed in DLTS spectra. The injection of minority carriers resulting from applying a forward bias generated signals for EHb (0.5 eV) and EHc (0.8 eV) hole traps while decreasing the EHa signal and increasing the net accepter concentration. The generation of EHa traps can likely be attributed to VN (3+/+) or NI (2+/+) defects based on the results of first-principles calculations. The EHb and EHc hole traps may have been associated with complex defects, including those that generated EHa traps, because these two traps appeared as the concentration of EHa traps decreased. [ABSTRACT FROM AUTHOR]

Herein, Al2O3/InAlGaN/GaN metal–insulator–semiconductor high‐electron‐mobility transistors (MIS‐HEMTs) using H2O vapor pretreatment to decrease the amount of deficient indium oxide (InOx) is successfully developed. InOx acts as an electron trap in the oxide on the surface of the InAlGaN barrier layer. It is clarified that when O2 plasma is used as an oxidant source for atomic‐layer‐deposited (ALD) Al2O3 (O2 plasma‐Al2O3), the forward breakdown voltage increases using the MIS‐HEMT, due to a high density and a low leakage current of O2 plasma‐Al2O3. Furthermore, when using O2 plasma‐Al2O3 for InAlGaN/GaN MIS‐HEMTs, H2O vapor pretreatment is effective in decreasing the amount of InOx and electron traps in the oxide on the surface, thus suppressing current collapse. These results demonstrate the improved output power characteristics of the fabricated Al2O3/InAlGaN/GaN MIS‐HEMT and show the potential of surface‐oxide‐controlled MIS structures as promising process technologies for next‐generation high‐power radio frequency devices. [ABSTRACT FROM AUTHOR]

An unrecoverable degradation of gate leakage is observed in AlGaN/GaN high electron mobility transistors (HEMTs) under high OFF‐state drain bias stress up to 200 V. Current‐mode deep‐level transient spectroscopy is developed for in situ observation of evolution of traps in the HEMTs before and after stress. It is revealed that two discrete traps, with activation energy of 0.54 and 0.69 eV, have converted into a deeper and broader trap (0.86 eV) after the stress, along with an increased apparent capture cross section (from 1.71 × 10−17–1.11 × 10−15 cm2 to 9.05 × 10−15 cm2). The conversion lowers down the tunneling barrier between metal and the AlGaN barrier, which facilitates trap‐assisted gate leakage in reversed biased AlGaN/GaN HEMTs. Engineering of deep traps in the AlGaN/GaN epilayers is essential for promoting and upgrading of power capability of GaN‐based RF HEMTs. [ABSTRACT FROM AUTHOR]

We propose a physics-based analytical model that accurately captures the effects of buffer traps on dc characteristics of gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs). The model is then semi-analytically extended to additionally include the transient behavior. Analytical formulations for the shift in the threshold voltage ${(}{V}_{\text {OFF}}{)}$ and two-dimensional electron gas (2-DEG) density due to the presence of buffer traps in the steady state are presented. In pulsed operation, technology computer-aided design (TCAD) simulations indicate that a time-dependent negative potential (NP) is developed under the gate, resulting in a modified ${V}_{\text {OFF}}$ and current collapse (CC). An expression for the modified ${V}_{\text {off}}$ helps capture the pulsed current–voltage characteristics. The model captures the dependence of bias, time, temperature, trap concentration, capture cross section area, and activation energy of traps on the steady-state and transient characteristics. The model is implemented in Verilog-A in an existing compact model framework using a diode and RC sub-circuit and validated using measured data and TCAD simulations. The modeling results are in excellent agreement with the experimental data and TCAD simulations. Since the model is physics-based, it requires fewer number of parameters compared to that in the existing models. [ABSTRACT FROM AUTHOR]

In this work, a hybrid combination structure of fin-channel array, gate-recessed structure, and LiNbO3 ferroelectric charge trap gate-stacked oxide layers was utilized in AlGaN/gallium nitride (GaN) enhancement-mode metal–oxide–semiconductor high-electron-mobility transistors (E-MOSHEMTs). The C+ ferroelectric polarization of the LiNbO3 blocking layer, deposited by a pulsed laser deposition system, increased the stored amount of electron charges in the HfO2 charge trap layer, leading to a high positive threshold voltage of 2.9 V for the enhancement-mode operation. In studying the initialization features, it was found that the threshold voltage shifted to a more positive voltage with an increase of initialization voltage. The devices changed to enhancement-mode from depletion-mode when the gate voltage larger than 4 V was applied to initialize the devices. Compared with a planar channel structure, the devices with 500-nm-wide fin-channel array structure improved the maximum extrinsic transconductance from 89.5 to 110.9 mS/mm, the subthreshold swing from 224.8 to 120.5 mV/dec, the extrinsic unit gain cutoff frequency from 5.0 to 7.4 GHz, the maximum oscillation frequency from 9.1 to 11.7 GHz, and the normalized noise power from $1.9\times 10^{-{14}}$ to $2.5\times 10^{-{15}}$ Hz−1. [ABSTRACT FROM AUTHOR]

This article presents how the emission time constant of deep-level traps is responsible for the achievable linearity (linearizability) degradation of gallium nitride high electron mobility transistor (GaN HEMT)-based power amplifiers. It is shown that the worst case scenario happens when the emission rate is on the order of the signal bandwidth, with substantial improvement when they begin to differ. Moreover, because of the strong temperature dependence of the emission time constant, self-heating is shown to play a major role in that linearizability degradation. To demonstrate the importance of the coupling of these two effects (electrothermal and trapping), two GaN HEMT dies with the same structure but different trap activation energies (which dictate the impact of temperature on trapping) were used. Digital predistortion tests using long-term evolution-like signals showed that these devices present different adjacent channel power ratios and normalized mean squared errors, after linearization with the same procedure, which varied with the signal bandwidth as theoretically predicted. [ABSTRACT FROM AUTHOR]

Trapping phenomena degrade the dynamic performance of wide-bandgap transistors. However, the identification of the related traps is challenging, especially in presence of non-ideal defects. In this paper, we propose a novel methodology (trap-state mapping) to extract trap parameters, based on the mathematical study of stretched exponential recovery kinetics. To demonstrate the effectiveness of the approach, we use it to identify the properties of traps in AlGaN/GaN transistors, submitted to hot-electron stress. After describing the mathematical framework, we demonstrate that the proposed methodology can univocally describe the properties of the distribution of trap states. In addition, to prove the validity and the usefulness of the model, the trap properties extracted mathematically are used as input for TCAD simulations. The results obtained by TCAD closely match the experimental transient curves, thus confirming the accuracy of the trap-state mapping procedure. This methodology can be adopted also on other technologies, thus constituting a universal approach for the analysis of multiexponential trapping kinetics. [ABSTRACT FROM AUTHOR]

A drain-controlled current-mode deep level transient spectroscopy (I-DLTS), was developed for investigation of Semi-ON-state current collapse in AlGaN/GaN high electron mobility transistors (HEMTs). By inserting a graded AlGaN back-barrier between the GaN channel and AlGaN buffer layer, hot-electron effect induced charging of buffer traps is effectively blocked, which contributes to a remarkable suppressed current collapse in AlGaN/GaN HEMTs under Semi-ON-state stress. A broad-distributed electron trap ${E}_{\text {T1}}$ , which features an energy level depth ${E}_{\text {C}}$ - ${E}_{\text {T}}$ and apparent capture cross section ${\sigma }_{\text {T}}$ of 0.25 ± 0.05 eV and $9.0\,\, {\pm } 1.0 {\times } 10^{-18}$ cm2, was verified to locate in the AlGaN buffer layer by I-DLTS. A combination of pulsed ${I}$ - ${V}$ and I-DLTS measurements, could be an effective method for in-situ study of current collapse mechanism in AlGaN/GaN HEMTs. [ABSTRACT FROM AUTHOR]

A cost-effective fabrication process is developed to improve the power performance of AlGaN/GaN High Electron Mobility Transistors (HEMTs). This process uses nitrogen ion (N+) implantation to form multiple parallel nanoribbons on AlGaN/GaN heterostructures, with a thin buffer layer (AlGaN/GaN NR-HEMTs). The stopping and range of ions in matter simulations of the N+ implantation combined with measured current-field characteristics reveal a good electrical isolation beneath the two-dimensional electron gas, resulting in substantial increase in the breakdown field of the NR-HEMTs, when compared to conventional AlGaN/GaN HEMTs. The fabricated AlGaN/GaN NR-HEMTs performed (i) an ON/OFF current ratio more than two orders of magnitude larger and (ii) a buffer leakage current more than one order of magnitude weaker than that of the conventional AlGaN/GaN HEMTs. The on-resistance, RON, and series resistance, RS, of AlGaN/GaN NR-HEMTs are both reduced by one order of magnitude when compared to those of the conventional AlGaN/GaN HEMTs. These have boosted the drive current density by up to 435%. Furthermore, we have found that the architecture of the AlGaN/GaN NR-HEMTs reduces the destructive impact of electron traps in the device. An optimized AlGaN/GaN NR-HEMT exhibited a better electrostatic integrity, a subthreshold slope of ∼210 mV/dec instead of 730 mV/dec for a conventional GaN HEMT. A higher linearity in the transconductance, gm, of NR-HEMTs is observed, twice of that of a conventional GaN HEMT. These results demonstrate the great interest of developed process technology of NR-HEMTs for high-power switching applications. [ABSTRACT FROM AUTHOR]

The electron trapping in AlGaN/GaN high-electron mobility transistors (HEMTs) with iron (Fe)-doped buffer is investigated through Drain Current Transient (DCT) measurements and TCAD physics-based 2D device simulations. The DCT characterization reveals two prominent deep-level electron traps E1 (∼0.5 eV) and E2 (∼0.6 eV) in the AlGaN/GaN HEMT. The measured DCT spectrum is analyzed at different trap-filling pulse durations (10 µs–100 ms) to obtain the information of trapping kinetics. As the first step in the simulation, the TCAD physical model parameters are calibrated by matching the simulated DC characteristics with the experimental data. It is shown that the TCAD model incorporating the acceptor-type trap at EC – 0.5 eV in the GaN buffer quantitatively reproduces the measured DCT spectra over the temperature range of 25–100 °C. To explore the buffer trapping effects, the simulated DCT is inspected by varying the activation energy, capture cross section, and concentration of the buffer trap. [ABSTRACT FROM AUTHOR]

The combined effects of proton irradiation and forward gate-bias stress on the interface traps of AlGaN/GaN heterostructure have been studied in this article. It is found that the effect of proton irradiation and forward gate-bias on the shift of flat band voltage $V_{\mathrm {FB}}$ is independent. By utilizing the frequency-dependent conductance technique, it is found that the trap density $D_{\mathrm {T}}$ at metal/AlGaN interface decreases after proton irradiation and the $D_{\mathrm {T}}$ at most energy levels increases after the following forward gate-bias. The $D_{\mathrm {T}}$ at AlGaN/GaN interface increases after proton irradiation and then decreases after the following forward gate-bias. The energy level range of metal/AlGaN interface traps reduces significantly under the forward gate-bias for the irradiated devices, however, that of AlGaN/GaN interface traps decreases little. In summary, the combined effect of proton irradiation and forward gate-bias stress on the interface traps is more complex than that on the bulk traps in AlGaN layer. [ABSTRACT FROM AUTHOR]

The presence of surface traps is an important phenomenon in AlGaN/GaN HEMT. The electrical and physical properties of these surface traps have been analyzed through the study of 2DEG electron concentration along with the variation of aluminum percentage in the barrier layer of HEMT. This analysis shows that from deep to shallow donors, the percentage change in electron density in 2DEG gets saturated (near 8%) with change in aluminum concentration. The depth of the quantum potential well below the Fermi level is also analyzed and is found to get saturated (near 2%) with aluminum percentage when surface donor states energy changes to deep from shallow. The physics behind this collective effect is also analyzed through band diagram too. The effect of surface donor traps on the surface potential also has been discussed in detail. These surface states are modeled as donor states. Deep donor (EC − ED = 1.4 eV) to shallow donor (EC − ED = 0.2 eV) surface traps are thoroughly studied for the donor concentration of 1011 to 1016 cm−2. This study involves an aluminum concentration variation from 5 to 50%. This paper for the first time presents the comprehensive TCAD study of surface donor and analysis of electron concentration in the channel and 2DEG formation at AlGaN–GaN interface. [ABSTRACT FROM AUTHOR]

In this work, we report a critical semi- ON-state drain stress voltage above which the gate current increases significantly and degrades permanently in AlGaN/GaN high electron mobility transistors (HEMTs). The observed critical voltage was found to be channel field-dependent by analyzing devices with different field plate lengths and passivation thicknesses, along with different gate–drain distances. Besides field dependence, the critical voltage was found to be carrier energy dependent by comparing the performance of devices subjected to semi- ON-state stress with devices under OFF-state stress. Experimentation on HEMTs with different buffer carbon doping variations revealed the degradation phenomenon to be a function of carbon doping in the GaN buffer. Furthermore, detailed electric field and electron temperature analysis revealed the drain edge to be a hot spot in accelerating interaction of hot electrons with traps in the GaN buffer leading to gate current degradation. A mechanism based on hot electron–buffer trap interaction-induced thermoelastic stress buildup and subsequent defect formation in the GaN buffer is proposed to explain the observed performance degradations. Observations such as a significant rise in channel temperature and accumulation of mechanical stress in the GaN buffer validate the proposed mechanism. Finally, the processes responsible for degradation lead to catastrophic failure of the device for longer stress times by the formation of cracks and pits in the GaN buffer, as validated by the postfailure field emission scanning electron microscopy (FESEM) analysis. [ABSTRACT FROM AUTHOR]

The impact of dynamic threshold voltage (${V}_{{\text {th}}}$) on the real-time characteristics of GaN direct-coupled FET logic (DCFL) inverter is investigated using an in-situ voltage tracking method. Due to the electrons’ trapping/de-trapping process at the gate dielectric/AlGaN-barrier interface, a two-step positive shift of the threshold input (${V}_{{\text {T}}}$) is observed in the device-under-test (DUT) inverter circuit, including the start-up periods and the self-adjusted dynamic equilibrium periods. The dependence of the dynamic ${V}_{{\text {T}}}$ upon different temperatures, input voltage magnitude, and operating frequency, is systematically studied and the underlying mechanism is revealed. Compared with the dc ${V}_{\text {T}}$ of the inverter of 3.6 V, the dynamic ${V}_{\text {T}}$ at 1 MHz switching with 8 V input amplitude shifts to ~5 V, which poses a challenge to GaN power integrated circuit (IC). [ABSTRACT FROM AUTHOR]

In this Letter, the degradation mechanism of Schottky p-type GaN (P-GaN) gate stack in GaN power devices under neutron irradiation is studied. After 1-MeV neutron irradiation at fluences of 6 × 1013 and 1 × 1014 neutron/cm2, device threshold voltage VTH is positively shifted and gate leakage current is increased, which indicates the degradation of Schottky P-GaN gate stack. By analyzing the gate current with Frenkel–Poole emission model, barrier height of Schottky P-GaN gate stack is reduced due to the traps induced by neutron irradiation. By employing capacitance–voltage (C–V) and pulse current–voltage (I–V) measurements, we find that the electron and hole traps induced by displacement damages dominate the degradation of gate characteristics after neutron irradiation. Electron traps at EC- (0.38–0.55) eV and hole traps at EV+ (0.56–0.62) eV with a density of 1011–1012 cm−2 eV−1 are shown in irradiated devices. Ionizations of VGa and Gai induced by neutron radiation as well as their interaction with dislocations significantly alter the energy band of P-GaN/AlGaN/GaN heterostructure gate stack. The trapping and de-trapping processes of VGa-related electron traps lead to positive shifts in VTH. Passivation of dislocations by Gai effectively lowers the barrier height for holes and increases the gate leakage current. Measures to improve the quality of P-GaN/AlGaN/GaN heterostructure or raise the potential barrier height can be taken to make the device more resistant to neutron radiation. This work depicts the physical process and mechanism of degradations in Schottky P-GaN gate stack, which can provide deeper insights into the analysis and field application of GaN power devices under neutron irradiation. [ABSTRACT FROM AUTHOR]

Novel normally-OFF AlGaN/GaN MIS-high electron mobility transistors (HEMTs) with a ZrOx charge trapping layer are proposed. The deposition of the ZrOx charge trapping layer on the partially recessed AlGaN in conjunction with the Al2O3 gate dielectric has been accomplished. The developed MIS-HEMTs exhibit a threshold voltage of 1.55 ± 0.4 V and a maximum drain current of 730 ± 6 mA/mm, while associated low ON-resistance of $7.1~\pm ~0.2~\Omega \cdot $ mm, for a gate to drain separation of 3 $\mu \text{m}$. The TCAD simulation results are presented to explore the charge trapping and de-trapping behaviors. Moreover, the devices exhibit a high breakdown voltage. The results indicate the merits of employing ZrOx charge trapping layer to realize the normally-OFF GaN devices with low ON-state resistance. [ABSTRACT FROM AUTHOR]

The gate and drain bias dependence of hot electron-induced degradation in GaN-based metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) was investigated in this work. Devices exhibit an abnormal increase in peak transconductance (${G}_{m}$ ,max) during hot carrier stress (HCS) and a partially quick recovery of that after removing the electrical stress. A physical model is proposed to explain the abnormal electrical characteristics caused by HCS. By using density functional theory (DFT), we calculated the energy for electrons to dehydrogenate preexisting [NGaH3]−1 complexes in GaN layer during stress. The dehydrogenation of defects affects the Gm,max of devices. Meanwhile, the neutralization of donor traps in AlGaN barrier layer also plays a significant role in the increase of Gm,max and the detrapping effect of electrons from these traps after removing the electrical stress accounts for the partially quick recovery of ${G}_{m, \text{max}}$. [ABSTRACT FROM AUTHOR]

In this study, we investigate the threshold voltage (${V} _{{{ \text {th}}}}$) instability of p-gate GaN HEMTs induced by gate bias. Experimental results are acquired by a custom pulse setup for two commercially available devices with an ohmic gate and a Schottky gate. A transient drain current change is observed, which corresponds to a shift of ${V} _{{{ \text {th}}}}$. A negative ${V} _{{{ \text {th}}}}$ instability is identified for the ohmic gate, a mostly positive for the Schottky gate that can also become negative depending on the gate bias voltage and duration. The impact of the gate-bias-induced ${V} _{{{ \text {th}}}}$ instability on the Schottky-gate device is significantly higher compared to the ohmic-gate device, but clearly noticeable at the nominal rated ON-state gate voltage for both devices. Electron depletion and trapping as well as hole accumulation and trapping are identified to cause this transient ${V} _{{{ \text {th}}}}$ instability. [ABSTRACT FROM AUTHOR]

The hybrid gate-recessed structure and ferroelectric charge trapping/storage stacked structure were used in AlGaN/GaN enhancement-mode metal–oxide–semiconductor high-electron mobility transistors (E-MOSHEMTs). The stacked structure consisted of a bottom 10-nm-thick Al2O3 tunnel oxide layer, a middle 4-nm-thick HfO2 charge trapping/storage layer, and a top 40-nm-thick LiNbO3 ferroelectric blocking layer. Using the postannealing process, a high polarized C+ domain of the pulsed laser-deposited LiNbO3 ferroelectric blocking layer was formed and the interface quality of the stacked structure was improved simultaneously. Consequently, positive threshold voltage for enhancement-mode operation was obtained. By studying the performances of the resulting devices, it was found that enhancement-mode behaviors were observed for initializing gate more than 5 V, and the threshold voltage of 1.6 V was obtained for initializing gate at 12 V. The high-frequency performances of the extrinsic unit gain cutoff frequency of 5.9 GHz and maximum oscillation frequency of 10.1 GHz were obtained. Furthermore, a low normalized noise power density of about $1.9\times 10^{-14}$ Hz−1 was achieved for the devices operating at a frequency of 10 Hz, a gate–source voltage of 5 V, and a drain–source voltage of 1 V. [ABSTRACT FROM AUTHOR]

The effects of high-energy (1 MeV) electron irradiation on the electrical and trapping properties of AlGaN/GaN high-electron-mobility transistors (HEMTs) are investigated systematically. When the irradiation fluence increases from ${5} \times {10}^{{12}}$ /cm2 to ${1} \times {10}^{{14}}$ /cm2, the drain–source current also increases and the threshold voltage shifts toward the negative direction. A Raman spectroscopy study shows that electron irradiation induces strain relaxation in the HEMT, which results in an improvement in the device’s electrical characteristics. In particular, three traps in the device are identified using the voltage-transient method and the trapping effects in the HEMT are investigated after the final irradiation. When compared with the transient voltages during the pristine stage, the absolute amplitudes of the three traps in the device decrease after irradiation, which indicates a reduction in the density of the traps. Furthermore, it is proposed that the time constants of the three traps increase while the energy levels remain unchanged, which is ascribed to the strain relaxation and the structural ordering of the defects after electron irradiation. The observed changes in the trapping behaviors are consistent with the improvement in the electrical properties of the device and the shift in the Raman spectra. [ABSTRACT FROM AUTHOR]

Buffer related electron trapping and hot electron injection are responsible for Ron degradation in devices, but the effects of substrate termination are still uncertain. In this work, both positive and negative substrate bias are applied to investigate the different vertical trapping mechanisms in 650 V gallium nitride (GaN) power devices. Ron shows an instant and significant increase under vertical bias stress, and the magnitude of downward buffer electron trapping induced Ron increase is relatively larger than that induced by upward trapping. Additionally, the substrate floated and grounded GaN devices are also submitted to both off-state and semi-on-state stresses to investigate the effects of substrate termination on hot electron injection induced Ron increase. The intensity of the upward electron trapping increases faster with temperature resulting in a higher Ron increase than the downward situation. The hot electron effect is only obvious when the substrate is grounded, suggesting that the main injection destination is not in the buffer. The substrate floated device exhibits a lower Ron increase after both off-state and semi-on-state stresses at elevated temperatures. Substrate floated packages are suggested to ensure reliable dynamic performance of device, especially for high voltage application design. [ABSTRACT FROM AUTHOR]

In this study, effect of post-fabrication annealing (PFA) on the electrical performance of the InAlN/GaN high electron mobility transistors (HEMTs) has been investigated. With PFA, the gate Schottky barrier height increases by 94 % (from 1.03 eV to 2.00 eV) and the interface trap state density (D it) is reduced by 27 %. Compared with the device without PFA, a higher on-current (11 %), a larger on/off current ratio (∼1 order), a higher transconductance (3 %), a reduced gate leakage current (84 %) and a lower subthreshold swing (10 %) are recorded in device with PFA. In addition, the improved electron mobility is observed and the reduction of polarization Coulomb field (PCF) scattering is proven in device with PFA due to the enhancement of polarization electrical field in InAlN/GaN heterostructure. [ABSTRACT FROM AUTHOR]

In this work, we have revealed the interplay of various charge sources (surface, polarization, and buffer) and their relative concentrations across the AlGaN/GaN epi-stack governing the electric field distribution and the breakdown mechanism in high electron mobility transistors (HEMTs). The investigations are carried out for Schottky, metal-insulator-semiconductor (MIS), and p-GaN gate stacks while accounting for possible GaN buffer types (Fe-doped and C-doped). A strong correlation between 3-terminal (3T) breakdown voltage, gate design, and relative concentration of various charges was found. % increase in 3T breakdown voltage when physical dimensions were doubled was also found to be strongly correlated with the relative concentration of various charges for both Fe- and C-doped buffer HEMTs. On the other hand, the 2T (source–drain, without gate, and GaN channel below gate) breakdown voltage was independent of all other parameters except buffer properties and physical dimensions. Physical insights are developed to explain the dependence of electric field distribution, carrier injection, and HEMT breakdown on the surface states, polarization charge, and buffer traps, as well as their relative concentrations for both the buffer types and all three gate types. These insights will help to design efficient surface passivation schemes and resolve ambiguities, often observed in experiments, in terms of location of peak electric field (drain side, or gate side or both) as well as OFF-state conduction and breakdown mechanism (gate injection, or punchthrough, or parasitic conduction through buffer or avalanche generation). [ABSTRACT FROM AUTHOR]

In this work, we present the substrate bias enhanced trap effects on time-dependent dielectric breakdown (TDDB) in GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) by experiment. Under different substrate biases, the shape parameter β and scale factor η of the Weibull distribution are extracted from the experimental data. A monotonical decrease in β from intrinsic breakdown to extrinsic breakdown relating to the hole-emission from the acceptor-like buffer traps with increased negative substrate biases has been observed, while η is increased at large positive substrate biases. This unexpected increase in η suggests that the donor-like buffer traps play an important role with a longer lifetime. The trap mechanisms, relating to percolation path establishment, are analyzed based on progressive breakdown (PBD). The capacitance–voltage characteristics are measured during each stress cycle confirming the hole fluence and electron injection in the gate-stack layer with different trap distributions under various substrate biases. Finally, 2-D device simulations are carried out to probe for physical insight into the traps on TDDB failure mechanisms. [ABSTRACT FROM AUTHOR]