High-Reflectivity A1-Pt Nanostructured Ohmic Contact to p-GaN

Ho Young Kim, Birck Nanotechnology Center and Department of Physics, Purdue University
P Deb, Birck Nanotechnology Center, School of Materials Engineering, Purdue University
Timothy D. Sands, Birck Nanotechnology Center, School of Materials Engineering, and School of Electrical and Computer Engineering, Purdue University

Abstract

The effect of nanoscale Pt islands on the electrical characteristics of contacts to p-type gallium nitride (GaN) has been investigated to explore the feasibility for the flip-chip configuration light-emitting diodes (LEDs) using an A1-based reflector. An as-deposited A1 contact to p-GaN with a net hole concentration of 3x10^17 cm^-3 was rectifying. However, an A1 contact with nanoscale Pt islands at the interface exhibited ohmic behavior. A specific contact resistivity of 2.1x10^-3 ohm•cm^2 and a reflectance of 84% at 460 nm were measured for the A1 contact with nanoscale Pt islands. Current-voltage temperature measurements revealed a Schottky barrier height reduction from 0.80 eV for the A1 contact to 0.58 eV for the A1 contact with nanoscale Pt islands. The barrier height reduction may be attributed to electric field enhancement and the enhanced tunneling due to the presence of the nanoscale Pt islands. This will offer an additional silver-free option for the p-type ohmic contact in flip-chip configuration LEDs. Theory suggests that the ohmic contact characteristics may be improved further with smaller Pt islands that will enhance tunneling across the interface with the GaN and in the vicinity of the Pt-A1 interface.