Hsin-Chu Chen

Recessed-gate AlGaN/GaN MISHEMTs are promising candidates for power electronics but often suffer from interface defects introduced during gate recessing, which degrade device performance and reliability. In this work, a supercritical fluid nitrogen passivation (SCFNP) technique is developed to address this limitation. The process is carried out at 180 °C under high pressure and enables efficient defect repair at both the Al₂O₃/AlGaN interface and the recessed-gate surface. Devices treated with SCFNP exhibited significantly improved electrical performance, including a positive threshold voltage (V_TH) shift to +2.2 V (extracted at I_D = 1 mA/mm), an increased maximum drain current of 600 mA/mm, a substantially reduced gate leakage current of 9.9 × 10^–8 mA/mm, and a high on/off current ratio of 5.0 × 10⁹. The gate leakage current decreased by nearly 2 orders of magnitude, while the OFF-state breakdown voltage (BV) increased by 27.8% (from 557 to 712 V). Dynamic on-resistance (R_ON) measurements further revealed a 25.6% reduction in current collapse under high-voltage stress. TCAD simulations corroborate these experimental results by demonstrating that reduced interface trap density suppresses peak electric fields at the drain edge, thereby validating the observed BV enhancement mechanism. Overall, SCFNP represents a low-temperature and scalable postfabrication passivation strategy for reliable GaN power devices.

This work presents a comprehensive analysis of the DC and RF characteristics of T-gate (0.25 μm) AlGaN/GaN high-electron-mobility transistors (HEMTs) by incorporating AlGaN back barriers with thicknesses of 50 and 15 nm into the epitaxial structure. The inclusion of the 50 nm AlGaN back barrier significantly enhanced the DC performance, achieving a high on/off current ratio of 1.5 × 10⁴, two orders of magnitude greater than that of the device employing a thinner 15 nm barrier. This improvement is due to a reduced drain-induced barrier lowering (DIBL) of 68 mV V⁻¹, compared to 72 mV V⁻¹ for the 15 nm AlGaN back barrier, highlighting the 50 nm back barrier effectiveness in mitigating short-channel effects. Additionally, the thicker back barrier effectively suppresses vertical carrier penetration, thereby lowering carrier trapping in the buffer layer and enhancing drain lag performance. The RF characteristics also showed notable performance, with small-signal and large-signal parameters demonstrating a cut-off frequency (F_T) of 59 GHz, a maximum oscillation frequency (F_MAX) of 138 GHz, a power-added efficiency (PAE) of 16.75%, and an output power (P_out) of 21.55 dBm at 28 GHz.

Revolutionizing semiconductor fabrication, ALD, ALE, and NBE deliver atomic-scale precision, driving unprecedented performance and scalability in next-generation miniaturized devices.

We successfully demonstrated a 72% reduction in current collapse under high-field driving conditions (V_D = 300 V) for AlGaN/GaN MISHEMT using low-temperature supercritical fluid nitridation (SCFN) treatment at 180 ^∘C for 1 h. A significant improvement in the OFF-state (V_G = -10 V) gate leakage current was observed in MISHEMT with SCFN treatment, resulting in a high breakdown voltage (BV) capability of up to V_D = 710 V (at 1 μA/mm), compared to only V_D = 110 V without SCFN. Furthermore, in terms of characteristics, the device was improved with a 4.6% increase in maximum drain current (I_D,max), a 2.9% increase in maximum transconductance (G_m,max), and an 11.1% decrease in drain-source ON resistance R_DS(on). These improvements can be attributed to the repairs of dangling bonds on the AlGaN surface and the elimination of the Al₂O₃/AlGaN interface traps, which collectively lead to improved performance and stability. Based on the abovementioned results, the X-ray photoelectron spectroscopy (XPS), conduction band edge of defect state density (D_it), and gate leakage trap-related hopping conduction mechanism were analyzed to explain the phenomenon.

The objective of this study is to optimize the trade-off between threshold voltage (V_TH) and maximum drain current (I_D,max) in recessed gate AlGaN/GaN metal insulator semiconductor high electron mobility transistor (MISHEMT) using atomic layer etching (ALE) technology, with technical computer-aided design (TCAD) simulations assisting in the analysis of the underlying mechanisms to demonstrate the high performance and reliability of GaN-based power application. A normally-off recessed gate MISHEMT with varying AlGaN remaining thickness (2 nm, 3 nm, and 5 nm) was fabricated using the ALE process, ensuring precise etch depth and minimal surface damage. The device with a 5 nm AlGaN remaining thickness exhibited excellent performance, with an I_D,max current of 347 mA mm⁻¹, a V_TH of +2.6 V, and a breakdown voltage (BV) of 830 V, compared to the AlGaN barrier with remaining thicknesses of 3 nm and 2 nm, which only reached 120 V and 75 V, respectively. The different recessed gate AlGaN remaining electric field distribution results were verified according to TCAD simulations. This is attributed to the hot electrons effect under the action of the high electric field to promote electrons to overcome potential energy barriers that are injected into a buffer, barrier, or insulating layers and trapped there, degrading off-state BV capability.

The objective of this study is to develop an efficient process to synthesize wafer scale p-type cuprous oxide (Cu2O) with the back-end-of-line (BEOL) compatible process (<400 °C). Metallic copper is deposited on SiO2/Si substrates followed by rapid thermal oxidation to oxidize it into large-area, uniform Cu2O. Bottom-gate Cu2O thin-film transistors (TFTs) were fabricated as gate dielectric on 100 nm thermal oxide. The results of the ID-VG curve demonstrate that we have successfully fabricated BEOL-compatible p-type Cu2O TFTs. The drain-off current can be achieved to 0.1 pA, with the highest on/off ratio reaching up to 6 orders. Significantly, the TFT with an on/off ratio of 106 is sufficient to meet the requirements for digital circuit applications, including logic circuits, and the BEOL-compatible process (<400 °C) can fulfill the demands of monolithic 3D integrated circuits, expanding the scope of functional integration applications. Additionally, positive bias stress reliability testing indicated a high-quality passivation layer. These findings suggest that material improvements have significantly enhanced the performance of Cu2O TFTs.

This study investigates the effect of O₂ plasma treatment on the physical and electrical properties of the surface region in Schottky-gate AlGaN/GaN high electron mobility transistor (HEMT). We demonstrate that O₂ plasma treatment significantly reduces the gate leakage current and enhances the on/off ratio by three orders of magnitude compared to devices without treatment. The O₂ plasma treatment removes organic chemical residue and forms Ga–O bonds on the AlGaN surface beneath the gate metal. X-ray photoelectron spectroscopy results indicate that the treatment effectively forms a Ga–O compound oxide layer, which provides surface passivation. Furthermore, atomic force microscope analysis reveals a 50% reduction in surface roughness after the O₂ plasma treatment. Using O₂ plasma oxidation treatment caused a shift in the threshold voltage (V_TH ) of Schottky-gate AlGaN/GaN HEMT. Initially measured at −5.26 V, the V_TH value shifted to +0.5 V. Furthermore, we also employ TCAD simulation to assist in the process developed during the manufacturing process. It is worth noting that the drain current decreases as the Ga–O compound oxide layer increases. This is due to effectively depleted the polarization charges at the AlGaN/GaN interfaces during E-mode operation when reducing the thickness of the AlGaN layer beneath the gate metal. Our results demonstrate the importance of O₂ plasma surface treatment in achieving optimal device performance. This study systematically discusses the effect of O₂ plasma on AlGaN/GaN surface properties and the formation of Ga–O bonding. It offers insights into developing high-performance Schottky-gate AlGaN/GaN HEMT.

In this study, we demonstrate breakdown voltage at 1500 V of GaN on a QST power device. The high breakdown voltage and low current collapse performance can be attributed to the higher quality of GaN buffer layers grown on QST substrates. This is primarily due to the matched coefficient of thermal expansion (CTE) with GaN and the enhanced mechanical strength. Based on computer-aided design (TCAD) simulations, the strong electric-field-induced trap-assisted thermionic field emissions (TA-TFEs) in the GaN on QST could be eliminated in the GaN buffer. This demonstration showed the potential of GaN on QST, and promises well-controlled performance and reliability under high-power operation conditions.