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In this work, we manifest that the epitaxial structure for p-GaN gate high-electron-mobility transistor is a versatile platform to develop electronics for operating in an extremely wide temperature range (X-WTR) from 2 to 675 K, with comprehensive X-WTR studies on device operation and circuit behaviors. The key enabler for the high-temperature operation is the wide bandgap that substantially suppresses the thermal excitation of the intrinsic carrier. However, for the low-temperature side, the two-dimensional electron and hole gas (2DEG and 2DHG) channels at the heterojunctions are formed by the temperature-insensitive polarization fields, which free the carriers from freezing out. The monolithically integrated GaN n-FET, p-FET, and the resultant complementary circuits are, therefore, shown to operate in X-WTR. [ABSTRACT FROM AUTHOR]

In this work, AlN polarization-enhancement interlayer (AlN-PEL) is adopted to enhance two-dimensional hole gas (2DHG) density in a p-GaN/AlN-PEL(∼2 nm)/AlGaN(<6 nm)/GaN heterostructure, aiming at monolithic integration of p/n-channel field effect transistors (p-FETs) on GaN-on-Si substrate. Owing to the strong built-in polarization of the AlN-PEL, high density 2DHG over 2.3 × 1013 cm−2 with good immunity to thermal freeze out effect is realized. Assisted by a two-step gate trench etching process, enhancement-mode (E-mode) buried-channel GaN p-FETs with temperature independent ON-resistance RON, and ON/OFF current ratio ION/IOFF (>108), have been fabricated. The fabricated p-FETs also deliver thermally stable subthreshold swing as well as threshold voltage Vth, and smaller Vth shift than that of p-FETs without the AlN-PEL, which is primarily due to enhanced 2DHG confinement by the AlN-PEL. The proposed structure is an attractive platform for monolithic integration of GaN-based logic and power devices for cryogenic applications as low as 10 K. [ABSTRACT FROM AUTHOR]

The p-GaN/AlGaN/GaN heterostructure, predominantly epitaxially grown on large-scale silicon wafers, has been widely used for producing consumer power switching devices and recently manifested favorable for developing GaN-based complementary devices and circuits. This work investigates the hole distribution and transport in this structure based on wide-temperature-range (20–600 K) Hall measurements and TCAD simulations. It is revealed that the p-channel thereof is composed of the bulk holes in the p-GaN and the two-dimensional hole gas (2DHG) at the p-GaN/AlGaN interface, and both substantially contribute to the lateral p-type conduction at room temperature. Their complementary temperature responses lead to conductivity enhancement at both high- and low-temperature regimes. The high-density (1.2 × 1013 cm−2) 2DHG is formed owing to the polarization-induced potential well and the ionization of the Mg acceptors that thermally diffused into the barrier during the epi-growth. Such ionized Mg acceptors would partially deplete the two-dimensional electron gas (2DEG) at the access region in the n-channel side where the p-GaN is removed and result in a trade-off between the carrier density of 2DHG and 2DEG. [ABSTRACT FROM AUTHOR]

Enhancement-mode (E-mode) p-channel gallium nitride (GaN) field-effect transistors (p-FETs) are essential components for GaN-based complementary logic circuits. For the ease of integration with n-FETs, they could be fabricated on the commercial p-GaN gate high-electron-mobility-transistor (HEMT) platform, on which the two-dimensional electron gas at the AlGaN/GaN hetero-interface is completely depleted in as-grown epi-structures. However, under the gated region where p-GaN is recessed and depleted at thermal equilibrium, a parasitic electron channel (PEC) could appear at the AlGaN/GaN interface. This Letter reports experimental investigations on the PEC with specifically designed structures, confirming that the PEC does exist but imposes limited impacts on electrical characteristics of p-FETs. When connected with an external contact, the PEC could act as a back gate to modulate the overlaying p-channel. If isolated from external contacts, which is the case of p-FETs under normal operations, electrons in the PEC would redistribute under the active region of p-FETs in the horizontal direction (i.e., parallel to the surface) under different biases but are mostly confined near the AlGaN/GaN interface in the vertical direction (i.e., perpendicular to the surface). [ABSTRACT FROM AUTHOR]

In this work, a deliberate etching-based top-down approach is proposed to fabricate the GaN nanorod (NR) Schottky barrier diode (SBD). As a key step during the fabrication, the impact of the wet-etching process on device performance is systematically studied. By virtue of the reduced surface states at the sidewall, the performance of NR SBD with the wet-etching process is substantially improved, delivering a forward turn-on voltage of 0.65 V, a current density of ∼10 kA/cm2 at 3 V, an ideality factor of 1.03, an ON/OFF current ratio of ∼1010, and no severe current collapse, along with a reverse breakdown voltage of 772 V. [ABSTRACT FROM AUTHOR]

In this work, by using an on-chip integrated Schottky-on-heterojunction light-emitting diode (SoHLED) which is seamlessly integrated with the AlGaN/GaN high electron mobility transistor (HEMT), we studied the effect of on-chip light illumination on the de-trapping processes of electrons from both surface and bulk traps. Surface trapping was generated by applying OFF-state drain bias stress, while bulk trapping was generated by applying positive substrate bias stress. The detrapping processes of surface and/or bulk traps were monitored by measuring the recovery of dynamic on-resistance Ron and/or threshold voltage Vth of the HEMT. The results show that the recovery processes of both dynamic Ron and threshold voltage Vth of the HEMT can be accelerated by the on-chip SoH-LED light illumination, demonstrating the potentiality of on-chip hybrid opto-HEMTs to minimize the influences of traps during dynamic operation of AlGaN/GaN power HEMTs. [ABSTRACT FROM AUTHOR]

In this work, by using an on-chip integrated Schottky-on-heterojunction light-emitting diode (SoHLED) which is seamlessly integrated with the AlGaN/GaN high electron mobility transistor (HEMT), we studied the effect of on-chip light illumination on the de-trapping processes of electrons from both surface and bulk traps. Surface trapping was generated by applying OFF-state drain bias stress, while bulk trapping was generated by applying positive substrate bias stress. The detrapping processes of surface and/or bulk traps were monitored by measuring the recovery of dynamic on-resistance Ron and/or threshold voltage Vth of the HEMT. The results show that the recovery processes of both dynamic Ron and threshold voltage Vth of the HEMT can be accelerated by the on-chip SoH-LED light illumination, demonstrating the potentiality of on-chip hybrid opto-HEMTs to minimize the influences of traps during dynamic operation of AlGaN/GaN power HEMTs. [ABSTRACT FROM AUTHOR]

This article was originally published online on 27 December 2023 with an error in the affiliation. The affiliation appears correct above. All online versions of this article were corrected on 4 April 2024.By Yingjie Wang; Sen Huang; Qimeng Jiang; Xinhua Wang; Zhongchen Ji; Jie Fan; Haibo Yin; Ke Wei; Xinyu Liu; Qian Sun and Kevin J. ChenReported by Author; Author; Author; Author; Author; Author; Author; Author; Author; Author; Author [Extracted from the article]

The surface of the p-GaN layer in Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) can be reinforced with enhanced immunity to hot electron bombardment by reconstructing the surface region of p-GaN into GaON. The surface region of p-GaN is treated by remote oxygen plasma and subsequently annealed at 800 °C, thereby becoming a thin crystalline gallium oxynitride (GaON) layer that will be in direct contact with the Schottky metal. The GaON exhibits a lower valence band maximum energy than that of the p-GaN, which leads to a higher Schottky barrier at the metal/GaON interface to holes and, thus, greatly suppresses the forward gate leakage. More importantly, with higher thermodynamic stability and a larger bandgap of ∼4.1 eV, the GaON reinforces the susceptible metal/p-GaN interface against the hot electrons and, thus, substantially enhances the long-term gate reliability of p-GaN gate HEMTs under forward bias stress. The high-temperature thermal process is indispensable for the surface reconstruction, without which the plasma oxidation only reduces the gate leakage but fails to prolong the time-dependent gate breakdown lifetime. [ABSTRACT FROM AUTHOR]

In this work, the impact ionization-induced OFF-state breakdown is revealed and systematically investigated in 100 V Schottky-type p-GaN gate high-electron-mobility transistors. Impact ionization is found to occur in the peak electric-field region at the source-terminated field-plate edge and is initiated by electrons injected from the source-side two-dimensional electron gas channel through the buffer layer. Hot electrons generated from impact ionization, when being captured by surface traps, could lead to redistribution and peak value reduction of electric-field. Consequently, the sudden rise in the OFF-state leakage current by impact ionization could be self-clamped temporally to avoid catastrophic rupture of the device. The impact ionization is further verified by the increase in dynamic OFF-state leakage current and a negative shift in threshold voltage, both of which result from positively charged holes (generated from impact ionization) drifting toward the gated channel. [ABSTRACT FROM AUTHOR]

The low-temperature gate reliability of Schottky-type p-GaN gate AlGaN/GaN heterojunction field-effect transistors under forward gate voltage stress is investigated. Both temperature-accelerated and voltage-accelerated time-dependent gate breakdown stress experiments are performed. The p-GaN gate exhibits a shorter time-to-failure at a lower temperature. It is found that the time-to-failure at "use conditions" predicted by acceleration tests at high gate bias stress could be overestimated at low temperatures. Such a discrepancy stems from the distinct dominant gate leakage mechanisms at high/low gate bias stress conditions. The dominant physical mechanism of the low-temperature gate leakage current is identified to be Poole–Frenkel emission at low gate bias and Fowler–Nordheim tunneling at high bias. From the physical model, a more accurate lifetime projection can be obtained for given use conditions. [ABSTRACT FROM AUTHOR]

The variations in surface potential and the Schottky barrier height [lowercase_phi_synonym]B in fluorine-plasma-treated AlxGa1-xN/GaN heterostructures are systematically studied by x-ray photoelectron spectroscopy, providing insights to the mechanisms underlying the strong threshold voltage (Vth) modulation achieved by the F plasma treatment technology. It is found that a large amount of AlF3 appeared on the surface after the treatment, indicating a fluorinated surface. In addition, the surface potential of Al0.25Ga0.75N/GaN heterostructure was increased by ∼0.38 eV during the first 60 s of the treatment and then rises slowly with additional treatment. Annealing at 400 °C in N2 ambient for 10 min does not affect the surface potential, but results in quick reduction in AlF3, consistent with the relative poor thermal stability of AlF3 reported in literature. [lowercase_phi_synonym]B between Ni and F-plasma-treated Al0.25Ga0.75N surface was extrapolated from the shift in Ga 2p3/2 core-level and exhibits a small increase of 0.20 eV. The enhanced [lowercase_phi_synonym]B is much smaller than the positive shift in Vth observed from high electron mobility transistors fabricated with the same treatment conditions, suggesting that the primary factor responsible for the conversion from depletion-mode to enhancement-mode AlxGa1-xN/GaN by F plasma treatment is not the surface modifications but rather the negative fixed charges carried by F ions in AlxGa1-xN/GaN heterostructures. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate an easy channel-engineering method using oxygen-plasma treatment followed by in-situ annealing before gate dielectric deposition on GaN. A crystalline GaON nanophase was identified to serve as an optimized channel layer in the gate region of E-mode GaN metal-insulator-semiconductor field-effect transistors (MIS-FETs). The atomic-scale element distribution and crystalline structure of the GaON nanophase were revealed by aberration-corrected scanning transmission electron microscopy. First-principles calculations further correlate the enhanced thermal stability with the atomic observation of the refined structure in the GaON nanophase. Owing to the atomically sharp gate-dielectric/channel interface and low interface trap density (Dit), the boosted performance of the E-mode MIS-FET was achieved with the GaON channel. This study not only validates an approach of local channel modification for high-performance normally off GaN MIS-FETs but also opens possibilities of utilizing this crystalline GaON nanophase as a promising channel material in various GaN devices. [ABSTRACT FROM AUTHOR]

We report the interface characterization of Al2O3/AlN/GaN MOS (metal-oxide-semiconductor) structures with an AlN interfacial layer. A thin monocrystal-like interfacial layer (AlN) is formed at the Al2O3/GaN to effectively block oxygen from the GaN surface and prevent the formation of detrimental Ga-O bonds. The suppression of Ga-O bonds is validated by X-ray photoelectron spectroscopy of the critical interface. Frequency-dispersion in C-V characteristics has been significantly reduced, owing to improved interface quality. Furthermore, using the conventional conductance method suitable for extracting the interface trap density Dit in MOS structures, Dit in the device with AlN was determined to be in the range of 1011-1012eV-1cm-2, showing one order of magnitude lower than that without AlN. Border traps near the gate-dielectric/GaN interface were identified and shown to be suppressed by the AlN interfacial layer as well. [ABSTRACT FROM AUTHOR]

High quality Al2O3 film grown by atomic layer deposition (ALD), with ozone (O3) as oxygen source, is demonstrated for fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Significant suppression of Al-O-H and Al-Al bonds in ALD-Al2O3 has been realized by substituting conventional H2O source with O3. A high dielectric breakdown E-field of 8.5 MV/cm and good TDDB behavior are achieved in a gate dielectric stack consisting of 13-nm O3-Al2O3 and 2-nm H2O-Al2O3 interfacial layer on recessed GaN. By using this 15-nm gate dielectric and a high-temperature gate-recess technique, the density of positive bulk/interface charges in normally-off AlGaN/GaN MIS-HEMTs is remarkably suppressed to as low as 0.9 x 1012cm-2, contributing to the realization of normally-off operation with a high threshold voltage of +1.6 V and a low specific ON-resistance RON,sp of 0.49 mΩ cm². [ABSTRACT FROM AUTHOR]

In this work, we attempt to reveal the underlying mechanisms of divergent V TH-thermal-stabilities in III-nitride metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) and MOS-Channel-HEMT (MOSC-HEMT). In marked contrast to MOSC-HEMT featuring temperature-independent VTH, MIS-HEMT with the same high-quality gate-dielectric/III-nitride interface and similar interface trap distribution exhibits manifest thermally induced VTH shift. The temperature-dependent VTH of MIS-HEMT is attributed to the polarized III-nitride barrier layer, which spatially separates the critical gate-dielectric/III-nitride interface from the channel and allows "deeper" interface trap levels emerging above the Fermi level at pinch-off. This model is further experimentally validated by distinct VG-driven Fermi level movements at the critical interfaces in MIS-HEMT and MOSC-HEMT. The mechanisms of polarized III-nitride barrier layer in influencing VTH-thermal-stability provide guidelines for the optimization of insulated-gate III-nitride power switching devices. [ABSTRACT FROM AUTHOR]

We report that a simple metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet emission at 3.4 eV at a small forward bias larger than ~2V at room temperature. Based on the surface states distribution of AlGaN, a mature impact-ionization-induced Fermi-level depinning model is proposed to explain the underlying mechanism of the electroluminescence (EL) process. By experimenting with different Schottky metals, Ni/Au and Pt/Au, we demonstrated that this EL phenomenon is a "universal" property of metal-AlGaN/GaN Schottky diodes. Since this light-emitting Schottky diode shares the same active structure and fabrication processes as the AlGaN/GaN high electron mobility transistors, straight-forward and seamless integration of photonic and electronic functional devices has been demonstrated on doping-free III-nitride heterostructures. Using a semitransparent Schottky drain electrode, an AlGaN/GaN high electron mobility light-emitting transistor is demonstrated. [ABSTRACT FROM AUTHOR]

Thermally stimulated current (TSC) spectroscopy and high-voltage back-gating measurement are utilized to study GaN buffer traps specific to AlGaN/GaN lateral heterojunction structures grown on a low-resistivity Si substrate. Three dominating deep-level traps in GaN buffer with activation energies of ΔET1~0.54 eV, ΔET2~0.65 eV, and ΔET3~0.75 eV are extracted from TSC spectroscopy in a vertical GaN-on-Si structure. High back-gate bias applied to the Si substrate could influence the drain current in an AlGaN/GaN-on-Si high-electron-mobility transistor in a way that cannot be explained with a simple field-effect model. By correlating the trap states identified in TSC with the back-gating measurement results, it is proposed that the ionization/deionization of both donor and acceptor traps are responsible for the generation of buffer space charges, which impose additional modulation to the 2DEG channel. [ABSTRACT FROM AUTHOR]

Iron(Fe)-doped InN (InN:Fe) layers have been grown by molecular beam epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from the semi-insulating property of Fe-doped GaN. However, this heavy n-type doping cannot be fully explained by doped Fe-concentration ([Fe]). Further analysis shows that more unintentionally doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and the surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. This work shows that Fe-doping is one of good choices to control electron density in InN. [ABSTRACT FROM AUTHOR]

We report the study of high-dielectric-constant (high-κ) dielectric LaLuO3 (LLO) thin film that is grown on AlGaN/GaN heterostructure by molecular beam deposition (MBD). The physical properties of LLO on AlGaN/GaN heterostrucure have been investigated with atomic force microscopy, x-ray photoelectron spectroscopy, and TEM. It is revealed that the MBD-grown 16 nm-thick LLO film is polycrystalline with a thin (∼2 nm) amorphous transition layer at the LLO/GaN interface. The bandgap of LLO is derived as 5.3 ± 0.04 eV from O1s energy loss spectrum. Capacitance-voltage (C-V) characteristics of a Ni-Au/LLO/III-nitride metal-insulator-semiconductor diode exhibit small frequency dispersion (<2%) and reveal a high effective dielectric constant of ∼28 for the LLO film. The LLO layer is shown to be effective in suppressing the reverse and forward leakage current in the MIS diode. In particular, the MIS diode forward current is reduced by 7 orders of magnitude at a forward bias of 1 V compared to a conventional Ni-Au/III-nitride Schottky diode. [ABSTRACT FROM AUTHOR]

A high electron mobility transistor (HEMT)-compatible power lateral field-effect rectifier (L-FER) with low turn-on voltage is demonstrated using the same fabrication process as that for normally off AlGaN/GaN HEMT, providing a low-cost solution for GaN power integrated circuits. The power rectifier features a Schottky-gate-controlled two-dimensional electron gas channel between the cathode and anode. By tying up the Schottky gate and anode together, the forward turn-on voltage of the rectifier is determined by the threshold voltage of the channel instead of the Schottky barrier. The L-FER with a drift length of 10 μm features a forward turn-on voltage of 0.63 V at a current density of 100 A/cm2. This device also exhibits a reverse breakdown voltage (BV) of 390 V at a current level of 1 mA/mm and a specific on resistance (RON,sp) of 1.4 mΩ cm2, yielding a figure of merit (BV2/RON,sp) of 108 MW/cm2. The excellent device performance, coupled with the lateral device structure and process compatibility with AlGaN/GaN HEMT, make the proposed L-FER a promising candidate for GaN power integrated circuits. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) devices using two-dimensional electron gas (2DEG) as interdigital transducers (IDTs) on AlGaN/GaN heterostructure has been demonstrated using a planar isolation technique based on the fluoride-based (CF4) plasma treatment technique. The rf characteristics of the SAW filters with planar 2DEG IDTs are compared with SAW devices that are made of metal IDTs or hybrid metal/2DEG IDTs. [ABSTRACT FROM AUTHOR]