ALD grown AZO contacts for AlGaN/GaN HEMT Device Applications

GaN-based high electron mobility transistor (HEMT) is a promising candidate for high-power and high-frequency applications due to it unique material properties. A low contact resistance (Rc) is curicial for the device performance including output power, high-efficiency, high-frequency and noise performances. Ti-based low-resistance ohmic contacts in AlGaN/GaN HEMT devices require high-temperature annealing (>800 oC) which can deteriorate material quality, surface morphology, and edge acuity of the metal stacks which makes it difficult to carry out further operations to form the gate region. Recently, non-alloyed ohmic contact which are not required high temperature post annealing have become a novel approach to form ohmic contacts. Aluminum-doped zinc oxide (AZO) films are widely used as a reliable electrode material for electronic and opto-electronic. ALD grown AZO films, which show a low electrical resistance, smooth surface morphology and suitable bandgap of 3.3 eV could be an alternative way of forming ohmic contacts for GaN based HEMT structures.This study focused on ALD grown AZO ohmic contacts and their comparison of alloyed and non-alloyed ohmic contacts GaN/AlGaN HEMT. Contact morphologies and contact resistance were investigated for AZO ohmic contacts, alloyed and non-alloyed ohmic contacts. Comparison of output characteristics of the fabricated HEMT devices was also performed