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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> of 5, 10, 25, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\boldsymbol {\mu }$ </tex-math></inline-formula>m, and their high-temperature characteristics were comprehensively investigated. The device with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5~\boldsymbol {\mu }$ </tex-math></inline-formula>m showed excellent rectification with high on/off ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{7}}$ </tex-math></inline-formula>, low ideality factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\eta } $ </tex-math></inline-formula> of ~1.65, and high effective Schottky barrier height <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\varphi } _{\text {eff}} $ </tex-math></inline-formula> of ~1.94 eV. In contrast, other devices with larger <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> showed larger <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\eta } $ </tex-math></inline-formula> (>3) and lower <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\varphi } _{\text {eff}}$ </tex-math></inline-formula> (~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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula>, 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}} =5$ </tex-math></inline-formula>, 10, 25, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\boldsymbol {\mu }$ </tex-math></inline-formula>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.