Impact of high-temperature Ohmic contact annealing process on AlN Schottky barrier diodes

Abstract

High-temperature Ohmic contact annealing is universally required in aluminum nitride (AlN) power device fabrication, yet its impact on adjacent AlN surfaces subsequently used for Schottky contact formation has never been investigated. We show that the Ohmic metal stack in combination with 950 °C rapid thermal processing markedly roughens the adjacent AlN surface, increasing the root mean square roughness from below 0.5 nm to approximately 2 nm and rendering AlN Schottky barrier diodes non-rectifying. This degradation is absent when the same thermal budget is applied without the metal stack, identifying that the thermal budget alone is not the causal factor. Cross-sectional scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy reveal AlOx- and Al-N-O-related interfacial layers formed at the Schottky contact region as a direct consequence of this annealing process. Sequential pretreatment by buffered oxide etching and atomic layer etching removes these layers, reduces the surface roughness to 0.3 nm, and recovers near-ideal Schottky characteristics with an ideality factor of 1.36. Temperature-dependent reverse current–voltage and multifrequency conductance analyses identify trap-assisted tunneling as the dominant reverse leakage mechanism. These findings uncover a previously unrecognized process-coupling effect between high-temperature Ohmic contact annealing and subsequent Schottky interface formation in AlN power device fabrication and provide a practical surface recovery route toward reliable rectifying contacts.