Fabrication and Characterization of a Novel Varistor Based on AlInGaN/GaN Heterojunction Epitaxy on High Resistance Silicon (111) Substrates

A high-resistance Si-based AlInGaN/GaN heterojunction epitaxy specifying AlN/AlGaN laminated buffer layers and AlInGaN barrier layer with 45% Al composition was successfully produced to show a high electron density of
$1.93\times10$
¹³
cm
⁻²
and mobility of 2829.24 cm
²
/Vs and based on which a novel varistor is proposed in this work. The varistor is composed with a narrow groove etched into the GaN channel and Ti/Al/Ni/Au (20/130/50/50 nm) metal electrodes attached to the epitaxy surface. The processes to fabricate the varistor were investigated in-depth, including a narrow groove etching based on dry-wet hybrid cyclic etching technology employing oxygen plasma and hydrochloric acid and an optimized metal electrodes ohmic contact process based on HCl:H
₂
O = 1:10 liquid surface treatment and annealing at 875 °C to achieve a low contact resistance of
$0.45 \Omega \cdot $
mm. The device with a groove width of
$3 ~\mu \text{m}$
and length of
$600 ~\mu \text{m}$
exhibits typical varistor characteristics with opening voltage (
$V_{{\mathrm {ON}}}$
) of 33.8 V and a high nonlinear coefficient of 82.97 in the current range from 1 to 10 mA. The
$V_{{\mathrm {ON}}}$
value of the varistors is directly proportional to the narrow groove width with a scaling coefficient of 10.18 V/
$\mu \text{m}$
, which means
$V_{{\mathrm {ON}}}$
can be adjusted by altering the width of the groove. The varistor with a simple structure could be used in GaN on-chip integrated switches, electro-static discharge (ESD) protection, and other applications.