Low Resistance Ohmic Contact On Epitaxial MOVPE-grown $\beta$-Ga$_2$O$_3$ and $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ Films

TL;DR

This study demonstrates record low resistance Ohmic contacts on MOVPE-grown heavily Si-doped $eta$-Ga$_2$O$_3$ and $eta$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films, advancing the potential for high-frequency power device applications.

Contribution

The paper reports the first realization of ultra-low resistance Ohmic contacts on MOVPE-grown $eta$-Ga$_2$O$_3$ and $eta$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films, with detailed analysis of contact resistance dependence on doping and Al content.

Findings

Record low contact resistance of 1.62e-7 Ohm.cm^2 on $eta$-Ga$_2$O$_3$ with high doping.

Contact resistance varies with Al content, increasing with higher Al percentages.

Annealing generally reduces contact resistance, especially in low Al content films.

Abstract

We report on the realization of record low resistance Ohmic contacts to MOVPE-grown heavily Si-doped $\beta$-Ga$_2$O$_3$ and $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ epitaxial films. Transfer length measurement (TLM) patterns were fabricated on the heavily Si-doped homoepitaxial $\beta$-Ga$_2$O$_3$ films with electron concentration (n) ranging from 1.77 to 3.23e20 cm^-3. Record low specific contact resistance and total contact resistance (Rc) of 1.62e-7 Ohm.cm^2 and 0.023 Ohm.mm were realized for $\beta$-Ga$_2$O$_3$: Si films with n > 3e20 cm^-3. TLM structures were also fabricated on heavily Si doped coherently strained $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ (x=12%, 17% and 22%) films. The film with 12% Al composition (n=1.23e20 cm^-3) showed \r{ho}c of 5.85e-6 Ohm.cm^2, but it increased to 2.19e-4 Ohm.cm^2 for a layer with a 22% Al composition. Annealing the samples post metal deposition has generally led to a decrease in contact resistance, but for high Al content $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$, the contact resistance did not change significantly after the annealing process. The low contact resistance values measured in this work are very promising for the fabrication of high frequency power devices.