Temperature Dependent Characteristics of Quasi-vertical AlN Schottky Diodes on Bulk AlN Substrate

TL;DR

This study reports on the fabrication and temperature-dependent behavior of AlN Schottky diodes, revealing high current densities, stable operation up to 300°C, and insights into carrier transport and leakage mechanisms.

Contribution

First detailed temperature-dependent characterization of MOCVD-grown quasi-vertical AlN Schottky diodes on bulk AlN substrates, including interface analysis and leakage mechanisms.

Findings

High current density exceeding 2 kA/cm2 at 10 V

Stable operation up to 300°C with increased current density at higher temperatures

Leakage dominated by Poole-Frenkel emission with a trap energy of ~0.34 eV

Abstract

We report on the fabrication and temperature-dependent characterization of MOCVD-grown quasi-vertical AlN Schottky barrier diodes (SBDs) on bulk AlN substrates. The SBDs exhibited high current densities exceeding 2 kA/cm2 at 10 V, with a turn-on voltage of ~3.0 V (at 1 A/cm^2) and an on/off ratio >10^9 at room temperature. Stable rectifying operation was maintained up to 300 C (the highest measured temperature), with a pronounced increase in current density at elevated temperatures due to thermally activated carrier transport, accompanied by an increase in extracted Schottky barrier height and a reduction in ideality factor. Capacitance voltage measurements showed strong temperature dependence due to the deep donor nature of Si in AlN, resulting in an increase in the net donor concentration (ND-NA) from ~5x10^17 cm-3 at 300 K to ~1x10^18 cm-3 at 373 K. Temperature-dependent reverse-bias characteristics were consistent with Poole-Frenkel emission as the dominant leakage mechanism, with an estimated trap energy of ~0.34 eV. Characterization using transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed a ~5 nm AlNxOy interfacial layer at the metal/semiconductor junction, which likely influences both forward and reverse transport. These results provide insight into carrier transport, leakage mechanisms, interface chemistry, and high-temperature characteristics, and guidance for the future development of high-performance AlN power devices.