【Member Papers】Xiamen University---Increase fixed charge at Al₂O₃/Ga₂O₃ interface for high-performance Ga₂O₃ trench Schottky barrier diodes by atomic nitrogen treatment

      Researchers from the Xiamen University have published a dissertation titled "Increase fixed charge at Al₂O₃/Ga₂O₃ interface for high-performance Ga₂O₃ trench Schottky barrier diodes by atomic nitrogen treatment" in Applied Physics Letters.

Project Support

      This work was supported by the National Natural Science Foundation of China (Grant No. 62171396) and the Shenzhen Science and Technology Program (Grant No. JCYJ20240813145617023).

Background

      β-Ga₂O₃, with its wide bandgap (4.5–4.9 eV) and high theoretical breakdown field (8 MV/cm), has emerged as a promising material for high-voltage and high-power applications. Compared to conventional wide bandgap semiconductors such as GaN and SiC, β-Ga₂O₃ offers significant advantages, including lower production costs due to its cost-effective melt growth method. This cost advantage makes β-Ga₂O₃ particularly attractive for large-scale commercial applications. Generally, conventional planar Ga₂O₃ Schottky barrier diodes (SBDs) suffer from severe electric field crowding at the Schottky contact edges under reverse bias, which triggers premature breakdown and elevates reverse leakage currents. However, trench Schottky barrier diode (TSBD) architecture tackles this challenge innovatively. By vertically embedding the Schottky contact within the trench structure, TSBDs effectively redistribute the electric field away from the contact periphery, thereby suppressing field crowding and enhancing the effective breakdown strength. Such fundamental improvements over planar architectures solidify TSBDs as a critical enabler for β-Ga₂O₃ to transcend the limitations of conventional SBDs in high-voltage scenarios.

Abstract

      We demonstrate a significant improvement in the breakdown voltage of vertical β-Ga₂O₃ metal-insulator-semiconductor (MIS) trench Schottky barrier diodes (TSBDs) through atomic nitrogen treatment at the Al₂O₃/β-Ga₂O₃ interface. The treated TSBDs show a breakdown voltage increasing from 832 to 1200 V while maintaining a low turn-on voltage of 0.9 V and a low specific on-resistance of 12.1 mΩ cm². As indicated by the x-ray photoelectron spectroscopy analysis, atomic nitrogen treatment reduces oxygen vacancies on the β-Ga₂O₃ surface and promotes the formation of ternary Ga–O–N compounds at the Al₂O₃/Ga₂O₃ interface. These compounds passivate ICP (Inductively Coupled Plasma)-induced defects on the Ga₂O₃ trench surface, reducing the leakage current in the Al₂O₃/Ga₂O₃ MIS TSBDs. Meanwhile, the atomic nitrogen treatment induces a positive shift in the flatband voltage of Ga₂O₃ MOS capacitors with Al₂O₃ dielectric, a sign of an increase in the fixed charge density (Q₁) at the Al₂O₃/Ga₂O₃ interface, which expands the depletion region under reverse bias and strengthens the contact barrier. These findings testify to the fact that atomic nitrogen treatment effectively optimizes the trench MIS interface, promising to an effective strategy for high-performance Ga₂O₃-based Schottky barrier diodes.

Summary

      In summary, we have demonstrated that atomic nitrogen treatment of the Al₂O₃/Ga₂O₃ interface in Ga₂O₃ TSBDs significantly improves device performance by increasing the breakdown voltage from 832 to 1200V while maintaining low V_on and R_on,sp. Meanwhile, the XPS spectra substantiate that the treatment reduces oxygen vacancies and facilitates formation of Ga-O-N compounds at the interface, the latter of which passivates defects and reduces leakage current. Moreover, the C–V measurements show that the treatment boosts the fixed charge density at the Al₂O₃/Ga₂O₃ interface, which expands the depletion region and further strengthens the contact barrier. TCAD simulations further confirm that the introduction of fixed negative charges at the Al₂O₃/Ga₂O₃ interface through atomic nitrogen treatment effectively optimizes electric field distribution, thereby enhancing the device’s breakdown capability. These findings demonstrate the effectiveness of atomic nitrogen treatment in advancing Ga₂O₃-based trench Schottky barrier diodes for high-power electronics, establishing this approach as a promising strategy to push the performance boundaries of gallium oxide devices.