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The effects of interface oxidation on the transport behavior of the 2-D electron gas (2DEG) in AlGaN/GaN heterostructures by plasma-enhanced-atomic-layer-deposited AlN (PEALD-AlN) passivation were investigated using temperature-dependent Hall-effect and X-ray photoelectron spectroscopy (XPS) characterizations. AlGaN/GaN heterostructure with a 4-nm-thick PEALD-AlN passivation exhibits good 2DEG transport behavior and stability at moderately high temperature (e.g., 275 °C). However, serious oxidation of the AlN/GaN (cap layer) interface occurs as the sample is heated up to 400 °C in low-pressure atmosphere, as verified by an increased Ga-O bond in Ga 3d core-level spectra. The oxidation leads to a significant reduction of 2.47 × 1012 cm-2 in the 2DEG density in the channel. A modified AlN passivation structure with Al2O3/AlN (10/4 nm) stack is shown to be able to effectively suppress the oxidation of the AlN/GaN interface, demonstrating an enhanced 2DEG density and high-temperature stability even when the sample is heated up to 500 °C. Based on XPS and 2DEG recovery experiments, it is suggested that acceptor-like deep levels have been generated in the near-surface region of AlGaN/GaN heterostructure because of the oxidation, and trapping of these deep levels results in significant depletion of the 2DEG in the channel. The effects of PEALD-AlN passivation on the strain in the AlGaN barrier of AlGaN/GaN heterostructures are also evaluated with high-resolution X-ray diffraction technique. [ABSTRACT FROM AUTHOR]

In this letter, we consider the problem of direction detection in deterministic interference and partially homogeneous noise. The target echoes, reflected by a distributed target, all come from the same direction. However, the signal steering vector is only known to lie in a subspace of dimension greater than one. The interference belongs to a subspace linearly independent of the signal subspace. We propose two effective detectors according to the two-step design criteria of the generalized likelihood ratio test and the Wald test. It is shown that the proposed detectors possess the constant false alarm rate property and have better detection performance than their counterparts. [ABSTRACT FROM PUBLISHER]

Effective interface engineering techniques in III-nitride heterojunction power devices, aiming at yielding high VTH stability in insulated-gate devices and suppressed current collapse in high-voltage switching operation, are of critical significance to enhance device performance and reliability. In this work, we present an interface enhancement technology featuring in situ low-damage NH3/Ar/N2 pre-gate plasma treatment prior to the ALD-Al2O3 deposition for high-performance III-nitride MIS-HEMTs. It is manifest that this technology can effectively remove the native oxide while forming a monocrystal-like nitridation interfacial-layer (NIL) on the III-nitride surface. The Al2O3(NIL)/GaN/AlGaN/GaN MIS-heterostructures with high-quality interface exhibit well-behaved electrical characteristics, including a small subthreshold swing of ∼64 mV/dec, a small hysteresis of ∼0.09 V, tiny f/T dispersions in the C- V characteristics, and low interface trap density of ∼1 × 1012-6 × 1012 cm−2eV−1. Cross-sectional TEM micrograph of the Al2O3/III-nitride gate stack with a monocrystal-like nitridation interfacial-layer (NIL). [ABSTRACT FROM AUTHOR]

Al2O3–AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) featuring indium tin oxide transparent gate electrode are fabricated for the purpose of evaluating the gate reliability. The transparent gate electrode allows electroluminescence (EL) observation in the region directly under the gate, which cannot be performed in conventional MIS-HEMTs with opaque gate electrode. Normally OFF transparent-gate MIS-HEMTs were realized by implanting fluorine ions into the AlGaN barrier prior to the deposition of Al2O3. The dependence of EL on bias condition was investigated with the color of EL resolved by filters. Gate dielectric degradation in MIS-HEMTs was induced by OFF state drain-bias stress, as detected by the increased gate leakage current. Location of the gate degradation could be clearly identified by EL imaging through the transparent gate. From the EL image, the passivation layer under the overhang of T-shaped gate is found to be vulnerable to OFF-state stress, which is confirmed by simulation. [ABSTRACT FROM AUTHOR]

We investigate in detail the influence of AlN passivation on dynamic ON-resistance ( \(R_{\mathrm{{\scriptstyle ON}}}\) ) and electric field ( \(E\) -field) distribution in high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate based on pulsed \(I\) – \(V\) measurements, electroluminescence (EL) microscopy, and 2-D physics-based numerical device simulations. It is found that the dynamic \(R_{\mathrm{{\scriptstyle ON}}}\) increase has been significantly suppressed to below 10% at various temperatures ranging from −50 to 200 °C owing to the effective and robust compensation of deep acceptor-like trap states at the AlN/GaN (passivation/cap) interface by the additional positive polarization charges induced in the epitaxial AlN thin passivation layer grown in a plasma-enhanced atomic layer deposition system. To the best of our knowledge, this is the first time that highly suppressed current collapse in an AlGaN/GaN HEMT on a Si substrate within a wide temperature range is ever reported. By monitoring the dynamic \(R_{\mathrm{{\scriptstyle ON}}}\) for 100 consecutive 133-kHz switching cycles, its variation is observed to be less than 2.5%, indicating excellent stability of the passivation effectiveness. The electric field in an AlN-passivated device is found to be well confined at the drain-side gate edge, as shown in EL measurement and numerical simulation results. This phenomenon directly suggests that the virtual gate effect arising from surface trap charging has been effectively alleviated by the AlN passivation technique. [ABSTRACT FROM AUTHOR]

The GaN-to-Si vertical conduction mechanisms on a low resistivity p-type (111) Si substrate under high-voltage operation are investigated using the temperature-dependent high-voltage C-V characterization and device simulation. It is found the deep depletion and weak inversion in Si will result in a high electric field at the GaN/Si interface and induce the impact ionization of Si. The generated electrons will be injected into GaN buffer layer, fill in buffer traps and act as free carriers in GaN, eventually leading to considerable vertical leakage in the AlGaN/GaN-on-Si structures. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a high-voltage low-standby power startup circuit for powering up the off-line switched-mode power supply (SMPS) during the startup period by exploiting monolithically integrated enhancement/depletion-mode metal–insulator–semiconductor high electron mobility transistors (E/D-mode MIS-HEMTs) fabricated on a GaN-on-Si power device platform. The E/D-mode MIS-HEMTs exhibit a threshold voltage of +1.2 and -11~V, respectively. The high-voltage D-mode device used in the demonstration features an OFF-state breakdown voltage of 640 V and a safe operating area with a thermal limitation of 11.6 W/mm, whereas the low-voltage E-mode device features a source-gate breakdown voltage of 98 V, satisfying the requirement of the startup circuit. The functionality of the startup circuit is successfully achieved with an input voltage range 10–200 V and a startup current of 1.08 mA. [ABSTRACT FROM AUTHOR]

In this paper, a surface potential-based terminal charge and capacitance model, including parasitic components for AlGaN/GaN HEMTs is developed. First, by solving the charge control equations, the sheet charge density in the channel is modeled with a close-form expression. Then, using this result, based on the surface potential definition, the intrinsic terminal charges and capacitances are derived consistently with current model. Finally, by introducing parasitic components, the capacitances for the full structure of the HEMT devices are given. The model is evaluated step-by-step with good agreements compared with the TCAD simulations and the experimental data. Meanwhile, the effects of bulk traps and surface traps in the capacitances are analyzed. The complete model, including currents and capacitances has been implemented in i-MOS platform for evaluations and circuit simulations. [ABSTRACT FROM PUBLISHER]

The threshold voltage ( VT) instability of metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) is investigated. In the enhancement-mode AlGaN/GaN MIS-HEMT fabricated by fluorine plasma implantation technique featuring Al2O3 gate dielectric, a hysteresis of 0.6 V in transfer characteristics is observed by quasi-static I - V (current-voltage) measurement, in which the gate bias is swept at a low rate (0.7 V/s). Pulsed transfer characteristics measurement, however, unveils much larger hysteresis under the same gate voltage swing. The VT-instability is attributed to the traps located at the dielectric/III-nitride interface as well as in the bulk of gate dielectric. It is proposed that pulsed measurement can count for the effect of fast traps (shallow traps) while the quasi-static measurement can only reflect slow traps (deep traps), and is more accurate for VT-instability evaluation. In addition, the existence of bulk traps is implied by a slow time-dependent shift of VT under large gate bias. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

High-frequency and high-temperature dynamic performance of plasma-enhanced atomic layer deposition AlN-passivated enhancement-mode GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) has been investigated under hard switching conditions. Low dynamic ON-resistance ( $R_{{\mathrm{{\scriptscriptstyle ON}}}})$ degradation with small frequency dispersion and weak temperature dependence is obtained. The effectiveness of AlN passivation in suppressing current collapse is proved even under hard switching operations, which, according to other reports of SiNx-passivated devices, could worsen the dynamic $R_{{\mathrm{{\scriptscriptstyle ON}}}}$ degradation due to the trapping of additional hot electrons. [ABSTRACT FROM AUTHOR]

Al2O3/AlGaN/GaN enhancement-mode metal-isolator-semiconductor high-electron-mobility transistor (MIS-HEMT) featuring a partially recessed (Al) GaN barrier was realized by a fluorine plasma implantation/etch technique. By properly adjusting the RF power driving the fluorine plasma, the fluorine plasma is able to produce two desirable results: 1) a well-controlled slow dry etching for gate recess and 2) implanting fluorine ions into the AlGaN barrier. The fluorine ions become negatively charged in the barrier layer and induce a positive shift in the threshold voltage. The proposed MIS-HEMT exhibits a threshold voltage ( V\mathrm {\mathbf {TH}}) of +0.6 V at a drain current of 10~\mu \textA /mm, a maximum drive current of 730 mA/mm, an ON-resistance of 7.07~\Omega \,\cdot \, mm, and an OFF-state breakdown voltage of 703 V at an OFF-state drain leakage current of 1~\mu \text{A} /mm. From room temperature to 200 °C, the device exhibits a small negative shift of V_{\mathrm {\mathbf {TH}}}$ ( $\sim 0.5$ V) that is attributed to the high-quality dielectric/F-implanted-(Al) GaN interface and the partially recessed barrier. [ABSTRACT FROM AUTHOR]

We report a high-performance normally-off Al2O3/AlN/GaN MOS-channel-high electron mobility transistor (MOSC-HEMT) featuring a monocrystalline AlN interfacial layer inserted between the amorphous Al2O3 gate dielectric and the GaN channel. The AlN interfacial layer effectively blocks oxygen from the GaN surface and prevents the formation of detrimental Ga-O bonds. Frequency-dispersion in C–V characteristics and threshold voltage hysteresis are effectively suppressed, owing to improved interface quality. The new MOSC-HEMTs exhibit a maximum drain current of 660 mA/mm, a field-effect mobility of 165 cm \(^{2}\) /V \(\cdot \) s, a high on/off drain current ratio of \(\sim 10^{10}\) , and low dynamic on-resistance degradation. [ABSTRACT FROM AUTHOR]

This letter reports a 0.2-\mum gate AlGaN/GaN high-electron-mobility transistors (HEMTs) on an Si substrate passivated with an AlN/SiNx (4/20 nm) stack layer. The 4-nm-thick AlN was grown by plasma-enhanced atomic-layer-deposition. The AlN/SiNx-passivated HEMTs exhibit a high maximum drain current of 930 mA/mm, an three-terminal OFF-state breakdown voltage (BVDS) of 119 V, and a small threshold voltage shift of 130 mV in a wide drain bias range (VDS=3-24~V). Owing to the additional positive polarization charge in the AlN passivation layer, the access resistance Rs in the GaN-on-Si HEMTs is significantly reduced while maintaining small parasitic gate-drain capacitance Cgd, contributing to a high power-gain cutoff frequency fMAX of 182 GHz and a high Johnson's figure of merit of BVDS\times f\,T of 6.43\times 10^12~V/s simultaneously. The accuracy of the RF performance is verified by a small signal modeling based on measured S-parameters. [ABSTRACT FROM AUTHOR]

We report an in situ low-damage pre-gate treatment technology in an atomic layer deposition (ALD) system prior to the ALD-Al2O3 deposition, to realize high-quality Al2O3/III\-nitride (III-N) interface. The technology effectively removes the poor quality native oxide on the III-N surface while forming an ultrathin monocrystal-like nitridation interlayer (NIL) between Al2O3 and III-N surface. With the pre-gate treatment technology, high-performance Al2O3(NIL)/GaN/AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors are demonstrated, exhibiting well-behaved electrical characteristics including suppressed gate leakage current, a small subthreshold slope of \sim64~mV/dec, and a small hysteresis of \sim0.09~V. [ABSTRACT FROM AUTHOR]

In this letter, 600-V normally-OFF SiNx/AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) is reported. Normally-OFF operation and low OFF-state gate leakage are obtained by using fluorine plasma ion implantation in conjunction with the adoption of a 17-nm SiNx thin film grown by plasma-enhanced chemical vapor deposition as the gate insulator. The normally-OFF MIS-HEMT exhibits a threshold voltage of +3.6~V, a drive current of 430 mA/mm at a gate bias of 14 V, a specific ON-resistance of 2.1 m\Omega\cdotcm^2 and an OFF-state breakdown voltage of 604 V at a drain leakage current of 1 \muA/mm with VGS=0~\rm V, and the substrate grounded. Effective current collapse suppression is obtained by AlN/SiNx passivation as proved by high-speed pulsed I\--V and low-speed high-voltage switching measurement results. [ABSTRACT FROM AUTHOR]

An effective passivation technique that yields low off-state leakage and low current collapse simultaneously in high-voltage (600-V) AlGaN/GaN high-electron-mobility transistors (HEMTs) is reported in this letter. The passivation structure consists of an AlN/\SiNx stack with 4-nm AlN deposited by plasma-enhanced atomic layer deposition and 50-nm \SiNx deposited by PECVD. The AlN/ \SiNx-passivated HEMTs with a gate–drain distance of 15 \mu\m exhibit a high maximum drain current of 900 mA/mm, a low off-state current of 0.7 \mu\A/mm at VDS = \600\ \V, and a steep subthreshold slope of 63 mV/dec. Compared with the static on-resistance of 1.3 \m\Omega \cdot \cm^2, the dynamic on-resistance after high off-state drain bias stress at 650 V only increases to 2.1 \m\Omega \cdot \cm^2. A high breakdown voltage of 632 V is achieved at a drain leakage current of 1 \mu\A/mm . [ABSTRACT FROM PUBLISHER]

The physical mechanism of passivation of AlGaN/GaN HEMTs by AlN thin film prepared with plasma-enhanced atomic layer deposition (PEALD) is investigated by characterizing \Ni- \Al2\O3/\AlN-\GaN/\AlGaN/\GaN metal–insulator–semiconductor (MIS) diodes. The dielectric stack \Al2\O3/\AlN (13/2 nm) exhibits similar capability in suppressing the current collapse in AlGaN/GaN HEMTs as the 4-nm PEALD-AlN thin film used in our previous work but delivers much lower vertical leakage to facilitate the capacitance–voltage characterizations. Exceptionally large negative bias ( < -\8\ \V) is required to deplete the 2-D electron gas in the MIS diode's C– V measurement. By virtue of quasi-static C–V characterization, it is revealed that positive fixed charges of \sim\3.2 \times \10^13\ \e/\cm^2 are introduced by the PEALD-AlN. The positive fixed charges are suggested to be polarization charges in the monocrystal-like PEALD-AlN. They can effectively compensate the high-density slow-response acceptor-like interface traps, resulting in effective suppression of current collapse. [ABSTRACT FROM PUBLISHER]