High-Temperature Electrical Characteristics of High-Voltage AlN Schottky Barrier Diodes on Single-Crystal AlN Substrates

In this work, high-voltage aluminum nitride (AlN) Schottky barrier diodes (SBDs) were fabricated on single-crystal AlN substrates with varying anode-to-cathode distances ${L}_{\text {AC}}$ of 5, 10, 25, and $50~\boldsymbol {\mu }$ m, and their high-temperature characteristics were comprehensively investigated. The device with ${L}_{\text {AC}}$ of $5~\boldsymbol {\mu }$ m showed excellent rectification with high on/off ratio of $10^{{7}}$ , low ideality factor $\boldsymbol {\eta } $ of ~1.65, and high effective Schottky barrier height $\boldsymbol {\varphi } _{\text {eff}} $ of ~1.94 eV. In contrast, other devices with larger ${L}_{\text {AC}}$ showed larger $\boldsymbol {\eta } $ (>3) and lower $\boldsymbol {\varphi } _{\text {eff}}$ (~1.1 eV). These findings suggest that AlN SBDs deviate from the thermionic emission (TE) model due to increased surface-induced current transport as the area of the devices increases. Furthermore, the temperature-dependent forward and reverse I–V characteristics were studied. At forward bias, the carrier transport regimes with respect to ${L}_{\text {AC}}$ and temperature were elucidated, providing guidance for designing AlN SBDs with ideal TE transport. The devices exhibited more pronounced inhomogeneous Schottky contact behavior with increasing ${L}_{\text {AC}}$ , indicating a larger deviation from the TE model. At reverse bias, different mechanisms were discussed for the reverse leakage of the AlN SBDs. Breakdown testing indicated the breakdown voltages (BVs) of 0.64, 1.1, 1.9, and 2.3 kV for devices with ${L}_{\text {AC}} =5$ , 10, 25, and $50~\boldsymbol {\mu }$ m, respectively. A field-plated structure was added to improve the BV further and reduce the leakage current due to mitigated electric field crowding at the anode edge. This work can serve as an important guideline for the future development of high-temperature and high-voltage AlN electronics.