Vertical β-(Al_xGa_1−x)₂O₃ Schottky Barrier Diodes with a BN Interlayer

Ultrawide bandgap (UWBG) semiconductors have attracted significant attention due to their potential applications in power electronics, optoelectronics, and RF electronics. Among these materials, β-Ga2O3 stands out as a promising candidate for UWBG semiconductors owing to its notable properties such as a high breakdown field of 8 MV/cm and a wide bandgap ranging from 4.6 to 4.9 eV. Additionally, it exhibits a high Baliga’s figure of merit (BFOM) in comparison to GaN and SiC. Moreover, the availability of large native substrates makes β-Ga₂O₃ highly promising for cost-effective high-voltage power electronics. By alloying β-Ga₂O₃ with Al₂O₃, (Al<i>_x</i>Ga<i>_1−x</i>)₂O₃ is produced with a tunable bandgap (e.g., 4.8-6.2 eV for <i>x</i> = 0 to 0.71). This alloy is expected to possess a higher BFOM than β-Ga₂O₃, making it more suitable for power electronic applications. Recent research has shown optoelectronic and power devices utilizing β-(Al<i>_x</i>Ga<i>_1–x</i>)₂O₃, yet most of these power devices operate laterally, which often underperforms compared to their theoretical limits. In contrast, vertical architectures dominate in commercial Si and SiC power devices, particularly in high-voltage and high-power applications. Vertical architectures offer advantages such as increased current and voltage handling capability, superior avalanche capability, absence of surface-related issues, enhanced heat dissipation, and reduced chip area.<br/><br/>Various methods have been proposed to enhance the reverse leakage current performance of Schottky barrier diodes (SBDs), including field plates, guard rings, and junction termination extensions. Additionally, metal–insulator–semiconductor (MIS) diodes have emerged as an appealing alternative to improve reverse performance. Introducing an ultrathin dielectric layer can effectively suppress reverse leakage current and mitigate electrical field effects at Schottky contact edges. Boron nitride (BN) is a promising candidate for MIS diodes due to its UWBG of 6 eV, high breakdown electric field of 12 MV/cm, high stability, and flat surface.<br/><br/>This study successfully demonstrated β-(Al<i>_x</i>Ga<i>_1–x</i>)₂O₃ metal–insulator–semiconductor (MIS) vertical diodes with a ~10 nm BN interlayer. β-(Al<i>_x</i>Ga<i>_1−x</i>)₂O₃ epilayer with an Al composition of 21% and a nominal Si doping of 2 × 10¹⁷ cm^-3, grown by molecular beam epitaxy. BN interlayer was directly deposited on the β-(Al<i>_x</i>Ga<i>_1–x</i>)₂O₃ epilayer using pulsed laser deposition. Pt/Ti/Au was utilized on the BN layer as the top Schottky contact, while Ti/Au served as the bottom Ohmic contact. Forward and reverse I-V measurements were conducted, revealing excellent rectification with a high on/off ratio of ∼10⁹. Remarkably, the insertion of the thin BN layer led to a nearly two-order decrease in reverse leakage current compared to traditional vertical β-(Al<i>_x</i>Ga<i>_1−x</i>)₂O₃ SBDs, with the turn-on voltage increasing from 1.5 to 2 V. This approach presents a promising solution to address reverse leakage current issues in β-(Al<i>_x</i>Ga<i>_1–x</i>)₂O₃-based vertical devices, paving the way for next-generation high-power electronics.