(Invited, Digital Presentation) Exploring the Potential and Limits of Gallium Oxide Electronics: In-Situ Dielectrics, Heterointegration and High-k Field Plates
Authors: Roy Saurav , Bhattacharyya Arkka , Krishnamoorthy Sriram 
Published: July 2022

The intrinsic properties of beta phase Gallium Oxide such as the high breakdown field strength makes it a very attractive material for next generation electronics. Rapid progress has been made over the last few years in pushing the performance of Gallium Oxide-based vertical Schottky diodes and lateral field effect transistors and impressive figure of merit has been reported. However, the device performance is farther from the expected performance based on intrinsic properties. Exploration of the intrinsic potential is rather limited by several factors such as the quality of dielectrics and dielectric/semiconductor interfaces, electric field management challenges due to the lack of p-type material, to name a few. In this work, we will highlight a few approaches to tackle some of these challenges.

(1) In-situ dielectrics: High quality dielectric-semiconductor interfaces are critical for reliable high-performance transistors. We report in situ metal–organic chemical vapor deposition of Al2O3 on β-Ga2O3 as a potentially better alternative to the most commonly used atomic layer deposition (ALD) [1]. The growth of Al2O3 is performed in the same reactor as Ga2O3 using trimethylaluminum and O2 as precursors without breaking the vacuum at a growth temperature of 600 °C. The fast and slow near interface traps at the Al2O3/β-Ga2O3 interface are identified and quantified using stressed capacitance–voltage (CV) measurements on metal oxide semiconductor capacitor (MOSCAP) structures. The density of shallow and deep level initially filled traps (Dit) are measured using ultraviolet-assisted CV technique. The average Dit for the MOSCAP is determined to be 6.4 × 1011 cm−2eV−1. The conduction band offset of the Al2O3/ Ga2O3 interface is also determined from CV measurements and found out to be 1.7 eV which is in close agreement with the existing literature reports of ALD Al2O3/Ga2O3 interface. The current–voltage characteristics are also analyzed and the average breakdown field is extracted to be approximately 5.8 MV cm−1.

(2) Field management using High-K field Plate: We report a vertical (001) β-Ga2O3 field-plated (FP) Schottky barrier diode (SBD) with a novel extreme permittivity dielectric field oxide [2] . A thin drift layer of 1.7μm was used to enable a punch-through (PT) field profile and very low differential specific on-resistance (Ron-sp) of 0.32 mΩ-cm2. The extreme permittivity field plate oxide facilitated the lateral spread of the electric field profile beyond the field plate edge and enabled a breakdown voltage (Vbr) of 687 V. The edge termination efficiency increases from 13.2%for non-field plated structure to 61% for high permittivity field plate structure. The high permittivity field plated SBD demonstrated a record high Baliga's figure of merit (BFOM) of 1.47 GW/cm2 showing the potential of Ga2O3 power devices for multi-kilovolt class applications.

(3) p-type III-nitride/Ga2O3 integration for field management: This work presents the simulation and analysis of a novel Ga 2 O 3 vertical Schottky diode with three different guard ring (GR) configurations to reduce the peak electric field at the metal edges [3]. Highly doped p-type GaN, p-type nonpolar AlGaN, and polarization-doped graded p-AlGaN are simulated and analyzed as the GR material, which forms a heterojunction with the Ga 2 O 3 drift layer. GR with nonpolar graded p-AlGaN with a bandgap larger than Ga 2 O 3 is found to show the best performance in terms of screening the electric field at the metal edges. The proposed GR configuration is also compared with a reported Ga 2 O 3 Schottky diode with no GR and a structure with high-resistive nitrogen-doped GR. The optimized design is predicted to have a breakdown voltage as high as 6.2 kV and a specific ON-resistance of 3.55 mΩ-cm 2, which leads to an excellent power figure of merit of 10.8 GW/cm 2.

The approaches discussed here can offer a pathway towards understanding the true potential and limitations of Gallium Oxide for extreme electric field devices. We acknowledge funding support from NSF (DMR-1931652) and the AFOSR MURI program (FA9550-18-1-0507).

References: [1] Roy, S., Chmielewski, A. E., Bhattacharyya, A., Ranga, P., Sun, R., Scarpulla, M. A., Alem, N., Krishnamoorthy, S., In Situ Dielectric Al2O3/β-Ga2O3 Interfaces Grown Using Metal–Organic Chemical Vapor Deposition. Adv. Electron. Mater. 2021, 7, 2100333.

[2] Roy, S., Bhattacharyya, A., Ranga, P., Splawn, H., Leach, J., & Krishnamoorthy, S. High-k Oxide Field-Plated Vertical (001) β-Ga2O3 Schottky Barrier Diode with Baliga’s Figure of Merit Over 1 GW/cm2. IEEE Electron Device Letters. (2021)

[3] Roy, S., Bhattacharyya, A., & Krishnamoorthy, S. Design of a β-Ga 2 O 3 Schottky Barrier Diode With p-Type III-Nitride Guard Ring for Enhanced Breakdown. IEEE Transactions on Electron Devices, 67(11), 4842-4848. (2020).