Electrostatic Effects of Self Trapped Holes in Gallium Oxide Devices

TL;DR

This study reveals how self-trapped holes generated by illumination affect the electrostatics and conduction in gallium oxide devices, using tunneling theory to explain photocurrent behavior.

Contribution

It introduces a tunneling-based model to explain photocurrent gain in gallium oxide, challenging traditional barrier-lowering explanations.

Findings

Photocurrent gain cannot be explained by conventional barrier lowering models.

Fowler-Nordheim tunneling accounts for the observed photocurrents and capacitance changes.

Illumination-induced charge significantly modifies device electrostatics.

Abstract

Gallium oxide is an ultra-wide bandgap semiconductor with exceptional properties for power electronics and UV-C optoelectronics, but its behavior under illumination remains poorly understood. In this work, we investigate how optically generated self-trapped holes influence electrostatics and current conduction in gallium oxide devices. Using a vertical Schottky photodiode with a semi-transparent Ni anode, we performed capacitance-voltage, current-voltage, and temperature-dependent I-V measurements under dark and above-bandgap illumination. Analysis of photocurrent gain reveals that conventional image-force barrier-lowering models require unrealistically high interfacial electric fields, suggesting the presence of an alternative mechanism. By applying Fowler-Nordheim tunneling theory, we reconcile measured photocurrents and photo-capacitance results with physically plausible fields and quantify the two-dimensional concentration of self-trapped holes. Our findings demonstrate that illumination-induced charge significantly alters device electrostatics. Understanding this tunneling-based photocurrent gain mechanism is critical for designing gallium oxide devices for UV-C detectors and power electronics.