Temperature dependent characteristics of Ti/Al/Ni/Au Ohmic contact on lattice-matched In0.17Al0.83N/GaN heterostructures

Abstract

In this work, we fabricated the transmission line model test structures of Ti/Al/Ni/Au Ohmic contact on the lattice-matched In0.17Al0.83 N/GaN heterostructures, grown on the silicon and sapphire substrates respectively, and studied the temperature-dependent characteristics of the sheet resistance (Rsh) and the specific contact resistivity (ρSC). The ln(Rsh)-ln(T) plot has two distinct linearly dependent regions: 1) At T < 200 K, the slope is close to zero, indicating the comparable impurity and phonon scattering components; 2) At T > 200 K, it becomes much smaller than zero, as the phonon scattering effect becomes significant. Increasing the temperature from 100 K to 523 K, ρSC exhibits a typical roll-over behavior: 1) At T < 350 K, a “metal-like” property is important, featuring a power-law coefficient of α ~ 1.95, which is ascribed to the formation of TiN protrusions across the InAlN barrier after the rapid thermal annealing; 2) At T > 350 K, a thermionic field emission current model agrees well with the experimental data points, and the effective barrier heights are extracted to be about 1.21 eV and 0.81 eV for the samples on the silicon and sapphire substrates, respectively.