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In this work, we studied the mechanisms and switching properties of AlGaN/GaN high-electron-mobility-transistors (HEMTs) passivated by amorphous-SiN x and monocrystal-like AlN. The effects of interface traps and polarization charges on current collapse are investigated by TCAD simulations and experimental characterizations. Surface/interface deep levels can be compensated by both shallow donor-like traps (SiN x passivation) and polarization charges (AlN passivation) at passivation/heterostructure interface, but with different levels of effectiveness under fast switching conditions. SiN x -passivation introduces shallow donor-like trap states with short time constant that favors a fast emission of trapped electrons in the access region and suppressed current collapse, but nevertheless exhibits more severe time-dependent recovery of dynamic on-resistance. For AlN passivation, interface traps are compensated by the fixed positive polarization charges and the off-state depletion region (in the 2DEG channel) is formed predominantly by electric-field effect, leading to an immediate accumulation of high channel electron concentration after switching the HEMT devices back to on-state and instant response of drain current to gate and drain bias. The field plate structure is necessary in SiN x -passivated devices for both current collapse suppression and electric field alleviation. With AlN passivation, the field plate can be solely designed for achieving more uniform electric field distribution for gate reliability concern without the concern of current collapse.

In this work, we investigated the mechanisms of nitride-based passivation (i.e. SiNx and AlN) and their impact on high-voltage switching of AlGaN/GaN heterojunction power transistors with TCAD simulations. It was found that they play a vital role for nitride-passivated devices to simultaneously achieve low dynamic ON-resistance (R-ON) and uncompromised breakdown capability. Simulated 2-D electrostatic OFF-state potential distributions and R-ON transients after switching suggested that the polarization charges together with fast-response shallow traps situated at the passivation/gap interface would improve the dynamic R-ON stability and at the same time effectively lower electric fields at the drain-side gate edge. The difference between SiNx and AlN as surface passivant for GaN HEMTs were also analyzed.

Passivation of group III-nitride hetero junction devices is described herein. The passivation facilitates simultaneous realization of effective/high current collapse suppression and low leakage current without the use of a sophisticated multiple-field plate technique. The passivation can be achieved by growing a charge-polarized AlN thin film on the surface of a group III-nitride based heterojunction device by plasma-enhanced atomic layer deposition such that positive polarization charges are induced at the interface to compensate for a majority of negative charges at the interface.

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 (VTH) of +0.6 V at a drain current of 10 μA/mm, a maximum drive current of 730 mA/mm, an ON-resistance of 7.07 Ω · mm, and an OFF-state breakdown voltage of 703 V at an OFF-state drain leakage current of 1 μA/mm. From room temperature to 200 °C, the device exhibits a small negative shift of VTH (∼0.5 V) that is attributed to the high-quality dielectric/F-implanted-(Al) GaN interface and the partially recessed barrier. © 1980-2012 IEEE.

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 ( RON) 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 RON degradation due to the trapping of additional hot electrons. © 2015 IEEE.

We report normally-off Al2O3/AlGaN/GaN metal-isolator-semiconductor high-electron-mobility transistor (MIS-HEMT) with improved thermal stability in DC and dynamic performance. The MIS-HEMTs featuring a partially recessed (Al)GaN barrier were realized by a fluorine-plasma implantation/etch technique. Both the well-controlled slow dry etching for gate recess and implanting fluorine ions into the AlGaN barrier are carried out with CF4 plasma at a relative high RF driving power. The partially recessed barrier leads to improved thermal stability, while the fluorine implantation can convert the device from depletion-mode to enhancement-mode without completely removing the barrier and sacrificing the high mobility heterojunction channel. From room temperature to 200 °C, the device exhibits improved thermal stability with a small negative shift of VTH (∼0.5 V) that is attributed to the high-quality dielectric/F-implanted-(Al)GaN interface and the partially recessed barrier. © 2015 IEEE.

Al2O3/AlGaN/GaN enhancement-mode (E-mode) metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) featuring a partially recessed (Al)GaN barrier was realized by a fluorine-plasma implantation/etch technique.

We report normally-off Al2O3/AlGaN/GaN metal isolator -semiconductor high-electron-mobility transistor (MISHEMT) with improved thermal stability in DC and dynamic performance. The MIS-HEMTs featuring a partially recessed (Al)GaN barrier were realized by a fluorine-plasma implantation/etch technique. Both the well-controlled slow dry etching for gate recess and implanting fluorine ions into the AlGaN barrier are carried out with CF4 plasma at a relative high RF driving power. The partially recessed barrier leads to improved thermal stability, while the fluorine implantation can convert the device from depletion-mode to enhancement-mode without completely removing the barrier and sacrificing the high mobility heterojunction channel. From room temperature to 200 C, the device exhibits improved thermal stability with a small negative shift of V-TH (-0.5 V) that is attributed to the high-quality dielectric/F-implanted-(Al)GaN interface and the partially recessed barrier.

A SiNx/AlN dielectric stack, which has been shown to provide a practical, robust, and effective passivation for GaN-based lateral heterojunction power switching devices, was characterized in this work to provide insights on the mechanisms of its current collapse suppression ability. The interface between the SiNx/AlN passivation stack and the AlGaN/GaN structure was characterized by investigating the interface state distribution and its chemical composition. Such interface was found to have much less trap states and significantly less oxidation than that in the heterostructure passivated by an Al2O3/AlN stack, validating that SiNx/AlN passivation is superior to Al2O3/AlN passivation. (C) 2015 The Japan Society of Applied Physics

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.

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 D-it in MOS structures, Dit in the device with AlN was determined to be in the range of 10(11)-10(12) eV(-1) cm(-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. (C) 2015 AIP Publishing LLC.

Passivation of group III-nitride heterojunction devices is described herein. The passivation facilitates simultaneous realization of effective/high current collapse suppression and low leakage current without the use of a sophisticated multiple-field plate technique. The passivation can be achieved by growing a charge-polarized AlN thin film on the surface of a group III-nitride based heterojunction device by plasma-enhanced atomic layer deposition such that positive polarization charges are induced at the interface to compensate for a majority of negative charges at the interface.

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). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report normally-off Al2O3/AlGaN/GaN metal-isolator-semiconductor high-electron-mobility transistor (MIS-HEMT) with improved thermal stability in DC and dynamic performance. The MIS-HEMTs featuring a partially recessed (Al)GaN barrier were realized by a fluorine-plasma implantation/etch technique. Both the well-controlled slow dry etching for gate recess and implanting fluorine ions into the AlGaN barrier are carried out with CF4 plasma at a relative high RF driving power. The partially recessed barrier leads to improved thermal stability, while the fluorine implantation can convert the device from depletion-mode to enhancement-mode without completely removing the barrier and sacrificing the high mobility heterojunction channel. From room temperature to 200 °C, the device exhibits improved thermal stability with a small negative shift of VTH (∼0.5 V) that is attributed to the high-quality dielectric/F-implanted-(Al)GaN interface and the partially recessed barrier.

We report normally-off Al2O3/AlGaN/GaN metal isolator -semiconductor high-electron-mobility transistor (MISHEMT) with improved thermal stability in DC and dynamic performance. The MIS-HEMTs featuring a partially recessed (Al)GaN barrier were realized by a fluorine-plasma implantation/etch technique. Both the well-controlled slow dry etching for gate recess and implanting fluorine ions into the AlGaN barrier are carried out with CF4 plasma at a relative high RF driving power. The partially recessed barrier leads to improved thermal stability, while the fluorine implantation can convert the device from depletion-mode to enhancement-mode without completely removing the barrier and sacrificing the high mobility heterojunction channel. From room temperature to 200 C, the device exhibits improved thermal stability with a small negative shift of V-TH (-0.5 V) that is attributed to the high-quality dielectric/F-implanted-(Al)GaN interface and the partially recessed barrier.

This letter reports a 0.2-&mu ; m 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 VDS× fT 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. © 2014 IEEE.

A high-temperature (180 °C) gate recess technique featuring low damage and in-situ self-clean capability, in combination with O3-assisted atomic-layer-deposition (ALD) of Al2O3 gate dielectric, is developed for fabrication of high performance normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs), which exhibit a threshold voltage of +1.6 V, a pulsed drive current of 1.1 A/mm, and low dynamic ON-resistance under hard-switching operation. Chlorine-based dry-etching residues (e.g. AlCl3 and GaCl3) are significantly reduced by increasing the wafer temperature during the gate recess to their characteristic desorption temperature, while defective bonds like Al-O-H and positive fixed charges in ALD-Al2O3 are significantly suppressed by substitution of H2O with O3 precursor. © 2014 IEEE.

We carried out detailed characterization and evaluation of dynamic performance of high-voltage AlGaN/GaN high electron mobility transistors (HEMTs) with AlN/SiNx passivation by means of pulsed I-V measurements. Transient OFF-to-ON switching tests verify the effectiveness of surface passivation by PE-ALD grown AlN epitaxial layer. The dynamic ON-resistance (RON) measured 350 ns after the switching event (500 ns) remains as low as only 1.08 times the static RON with an OFF-state drain bias of 60 V. Less than 10% degradation in dynamic RON is achieved under 40-V switching at various frequencies of 1-133 kHz within a wide temperature range of.50-200 °C. The stability of dynamic RON is also confirmed with a simple approach by monitoring the pulsed current at a drain bias of ∼1 V for 100 consecutive switching cycles.

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). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

GaN heterojunction power transistors have shown great promise to replace silicon power MOSFETs in next-generation power converters, owing to their remarkable performance in terms of ON-resistance (RON), breakdown voltage, switching speed, and high-temperature operation, breaking the so-called “Si limit”. Despite the advantages resulting from superior material properties such as high carrier density, high electron mobility and saturation velocity of the 2-D electron gas (2DEG) channel, large critical breakdown electric field, and extremely low intrinsic carrier density, it still remains challenging for GaN devices to reach their performance limit. This is mainly caused by a transient increase in RON under switching conditions, which is commonly known as dynamic RON or current collapse that would lead to lower conversion efficiency and instability issues in a power conversion system. This thesis focuses on the development of passivation technologies for suppressing surface-state-induced current collapse in GaN high-voltage power transistors. An effective passivation technique based on compensation of interface traps with polarization charges in AlN thin film has been recently demonstrated for depletion mode (D-mode) AlGaN/GaN high electron mobility transistors (HEMTs). A more practical and cost-effective solution using an AlN/SiNx stack structure that features higher resistance to moisture and oxygen and compatibility with field plate structures is further designed and developed for 600 V AlGaN/GaN HEMTs that exhibit low dynamic RON and low OFF-state leakage simultaneously. Detailed analysis of the AlN/SiNx-passivated HEMT in support of the passivation mechanism is carried out with temperature-dependent pulsed I–V and high-voltage switching characterization, electroluminescence (EL) microscopy, and TCAD simulations. Since enhancement mode (E-mode) operation is highly desirable for power switches from fa