Low-resistance and thermally stable indium tin oxide Ohmic contacts on strained p- In0.15 Ga0.85 Np-GaN layer

We report on the formation of low-resistance and thermally stable indium tin oxide (ITO) Ohmic contacts on p-GaN using a strained p-InGaN (5 nm) layer. Unlike as-deposited ITO contacts on p-GaN, the as-deposited contacts to a strained p-InGaNp-GaN layer exhibit Ohmic behavior. The current-voltage characteristics of the ITOInGaNGaN contacts are further improved upon annealing at 550 °C for 1 min and the specific contact resistance is 3.2 (±0.8) × 10-5 cm2. In addition, the contact resistivity and surface morphology of the ITOInGaNGaN contacts annealed for 30 min are only slightly increased, confirming the thermal stability of this scheme. Based on the electrical and Auger spectroscopic data, the low contact resistivity and thermal stability of the ITOInGaNGaN contacts are described in terms of the polarization effect, increased acceptor concentration, and formation of diffusion barrier layer at the interface.