β-Gallium Oxide: Progress in Epitaxial Materials and Power Devices

The availability of shallow donors and large area melt-grown bulk substrates are the key enablers for next-generation power devices based on β-Ga₂O₃. Three key results will be highlighted in this presentation. (1) We demonstrate a hybrid low temperature - high temperature (LT-HT) buffer/channel stack growth using metal organic vapor phase epitaxy with record carrier mobility values (range of 196–85 cm²/Vs) over four orders of doping range (2×10¹⁶– 1×10²⁰ cm⁻³). Record electron mobility of 110 cm²/Vs is also demonstrated in delta-doped (2D) channels (n_s = 9.2×10¹² cm^-2). The improvement in transport properties was achieved mainly by realizing pristine doped channels, eliminating undesired parasitic conduction paths, and minimizing carrier compensation. Lateral transistors utilizing these uniformly Si-doped channels with LT buffers exhibit exceptional device performance. Planar and tri-gate transistors showed very low reverse leakage for breakdown voltages up to 3 kV. Due to enhanced electron mobility, these devices were able to exhibit low on-state resistances for a given device dimension. In conjunction with effective electric-field management (achieved max average breakdown field of over 4 MV/cm with tri-gate architectures), these devices were able to deliver a high power figure of merit of ∼1 GW/cm². (2) We report on the growth and characterization of in-situ Al₂O₃ dielectric on (010) β-Ga₂O₃deposited using metalorganic chemical vapor deposition (MOCVD) to enhance the dielectric quality and lifetime. The dielectrics grown at 600 °C exhibited higher interface trap densities (D_t= 3.2×10¹² cm^-2) and lower breakdown fields (E_BR=6 MV/cm) when compared to the dielectrics grown at 800 °C (E_BR= 10 MV/cm, D_t=5.4×10¹¹ cm^-2) as is evident from the hysteresis and the trap density vs energy characterization which were determined using deep-UV assisted CV measurements and the current-voltage characteristics of the MOS capacitor test structures. The temperature-modulated dielectric sample (interfacial layer grown at 800 °C, and the bulk dielectric grown at 600 °C) has higher breakdown strength (E_BR=7.7 MV/cm) and lower trap density (D_t= 1.1×10¹² cm^-2) compared to the dielectric grown at 600 °C. Time dependent dielectric breakdown (TDDB) (current vs stress time) was performed to characterize the long-term reliability of the grown dielectrics.This approach of in-situ dielectric deposition on β-Ga₂O₃ can pave the way for promising robust gate dielectrics for future β-Ga₂O₃ based high performance MOSFETs due to its promise of improved interface and bulk quality and long-term reliability compared to other conventional dielectric deposition techniques.(3) We report large area (1mm² and 4mm² ) β-Ga₂O₃ trench Schottky barrier diodes with high-k dielectric RESURF.The breakdown voltage of the BTO field-plated SBD increases to 2.1 kV from 816 V (planar SBD) whereas the breakdown voltage increases to 2.8-3kV for the trench SBD with high-k RESURF. The 1 mm² trench SBD exhibits a current of 3.7A(Pulsed)/2.9A(DC) and the 4mm² trench SBD exhibits a current of 15A(Pulsed)/9A(DC) at 5V. The breakdown (catastrophic) voltage of the 1mm² and 4mm² trench SBDs are measured to be 1.4 and 1.8kV, respectively. The rapid progress in the realization of high purity materials, high quality dielectrics , experimentally demonstrated high electric field handling capability along with a pathway to scaling to high absolute current ratings, indicates the promise and potential of Gallium Oxide for next-generation power electronics. This material is based upon work supported by the II-VI Block Gift Program and the Air Force Office of Scientific Research MURI award