Department of Electric Materials Engineering, Kwangwoon University, Seoul 01897, Korea (Received June 13, 2024; Revised July 8, 2024; Accepted July 10, 2024) Abstract: Wide bandgap (WBG) devices, especially SiC, are gaining traction as materials for high-power EV conversion devices due to their superior efficiency and switching capabilities compared to Si-based power devices. SiC allows for high power, high temperature, and high frequency applications because of its outstanding thermal conductivity, saturation velocity, and dielectric breakdown field. SiC-based MPS diodes combine the advantages of SiC-based SBDs and PiN diodes, allowing high-frequency switching operation with low leakage currents under high voltage conditions. However, MPS diodes exhibit snapback phenomena influenced by the P⁺ region’s size, necessitating optimization. A TCAD simulation studied the impact of the P+ region’s depth and width on MPS diode performance. Increasing the P⁺ width raised the On-specific resistance (R_on,sp) and lowered the maximum voltage during snapback (V_snap). Increasing the depth decreased both Breakdown voltage (BV) and V_snap. A trade-off between the semiconductor performance index BFOM and V_snap was identified, leading to optimized dimensions. The optimized MPS diode shows a low V_snap of about 3.89 V and a high BFOM of 1.72 GW·㎠, highlighting its potential as a next-generation high-performance power conversion device.

Gallium oxide (Ga₂O₃) is emerging as a next-generation power semiconductor material due to its excellent electrical properties, including an ultra-wide bandgap of approximately 4.8 eV and a breakdown electric field of about 7 MV/cm. However, its low thermal conductivity of around 0.13 W/cmK presents significant challenges to the performance and reliability of Ga₂O₃- based devices. In this study, we employed the Silvaco TCAD simulator to analyze the thermal and electrical characteristics of Ga₂O₃ Schottky barrier diodes (SBDs) with heat sinks of varying thermal conductivities. The results demonstrate that heat sinks with higher thermal conductivity effectively mitigate the temperature rise in the device, leading to an increase in current density. The limitation in heat dissipation due to parasitic on-state resistance not only affects device performance but also impacts longterm reliability. Therefore, this study contributes to the development of effective thermal management strategies for Ga₂O₃-based power semiconductors.

This reports the electrical properties of single-crystal β-gallium oxide (β-Ga₂O₃) vertical Schottky barrier diodes (SBDs) with a different guard ring structure. The vertical Schottky barrier diodes (V-SBDs) were fabricated with two types guard ring structures, one is with metal deposited on the Al₂O₃ passivation layer (film guard ring: FGR) and the other is with vias formed in the Al₂O₃ passivation layer to allow the metal to contact the Ga₂O₃ surface (metal guard ring: MGR). The forward current values of FGR and MGR V-SBD are 955 mA and 666 mA at 9 V, respectively, and the specific on-resistance (Ron,sp) is 5.9 mΩ·cm² and 29 mΩ·cm². The series resistance (Rs) in the nonlinear section extracted using Cheung’s formula was 6 Ω, 4.8 Ω for FGR V-SBD, 10.7 Ω, 6.7 Ω for MGR V-SBD, respectively, and the breakdown voltage was 528 V for FGR V-SBD and 358 V for MGR V-SBD. Degradation of electrical characteristics of the MGR V-SBD can be attributed to the increased reverse leakage current caused by the guard ring structure, and it is expected that the electrical performance can be improved by preventing premature leakage current when an appropriate reverse voltage is applied to the guard ring area. On the other hand, FGR V-SBD shows overall better electrical properties than MGR V-SBD because Al₂O₃ was widely deposited on the Ga₂O₃ surface, which prevent leakage current on the Ga₂O₃ surface.

In this paper, we discussed the effect of field plate dielectric materials such as silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and hafnium oxide (HfO₂) on the breakdown characteristics of β-Ga₂O₃ Schottky barrier diodes (SBDs). The breakdown voltage (BV) of the SBDs with a field plate was higher than that of SBDs without a field plate. The higher dielectric constant of HfO₂ contributed to the superior reduction in electric field concentration at the Schottky junction edge from 5.4 to 2.4 MV/cm. The SBDs with HfO₂ field plate showed the highest BV of 720 V, and constant specific on-resistance (R_on,sp) of 5.6 mΩ·㎠, resulting in the highest Baliga’s figure-of-merit (BFOM) of 92.0 MW/㎠. We also investigated the effect of dielectric thickness and field plate length on BV.

We investigated deep levels in n-type 4H-SiC epitaxy layer of the Schottky barrier diodes (SBD) and Junction Barrier Schottky (JBS) diodes by using deep level transient spectroscopy (DLTS). The I-V characteristics of the JBS devices show ~100 times lower leakage current level than SBDs owing to the grid structures in JBS. The reliable responses of the diodes for deep level transient analysis showed from C-V characteristics. Several deep electron traps were revealed by DLTS measurements in epitaxial layers in 4H-SiC. In both types of diodes, the peaks corresponding to shallow energy levels were observed with slightly different values of 0.132 eV for JBS and 0.186 eV for SBDs. The two remarkable deep level peaks (J2 and J3) have been obtained with 0.257 eV and 0.273 eV in JBS, and they were analyzed to have a similar trap concentration of ~10¹⁴ cm^-3. The comparison results showed that the defects could be related with device fabrication procedures such as ion-implantation and growth.

Abstract: We have fabricated schottky barrier diode (SBDs) using polar (c-plane) and non polar (a-, m-plane) n-type 6H-SiC wafers. Ni/SiC ohmic contact was accomplished on the backside of the SiC wafers by thermal evaporation and annealed for 20minutes at 950℃ in mixture gas (N(2) 90% + H(2) balanced). The specific contact resistance was 3.6×10-4 Ω㎝2 after annealing at 950℃. The XRD results of the alloyed contact layer show that formation of NiSi2 layer might be responsible for the ohmic contact. The active rectifying electrode was formed by the same thermal evaporation of Ni thin film on topside of the SiC wafers and annealed for 5 minutes at 500℃ in mixture gas (N(2) 90% + H(2) balanced). The electrical properties of SBDs have been characterized by means of I-V and C-V curves. The forward voltage drop is about 0.95 V, 0.8 V and 0.8 V for c-, a- and m-plane SiC SBDs respectively. The ideality factor (η) of all SBDs have been calculated from log(I)-V plot. The values of ideality factor were 1.46, 1.46 and 1.61 for c-, a- and m-plane SiC SBDs, respectively. The schottky barrier height (SBH) of all SBDs have been calculated from C-V curve. The values of SBH were 1.37 eV, 1.09 eV and 1.02 eV for c-, a- and m-plane SiC SBDs, respectively.