Optimized subsequent-annealing-free Ni/Ag based metallization contact to p-type GaN for vertical light emitting diodes with high yield and extremely low operating voltage (2.75 V@350 mA, >95%)

A Ni/Ag based metallization contact to p-type GaN (p-GaN), free of a subsequent annealing process, was optimized to couple excellent optical reflectance (as high as 90% at 460 nm) and electrical characteristics (specific contact resistivity as low as 2.1 × 10−5 Ω cm2) simultaneously. Vertical light emitting diode devices with optimized Ni/Ag/Pt/Au contacts were fabricated, and they exhibited extremely low forward voltage (2.75 V@350 mA, approaching its corresponding theoretical limit) and light output power was improved by 35%. Chip-on-wafer mapping tests revealed significantly high yield and excellent uniformity across the wafer. X-ray diffraction results indicated improved crystalline quality and more favourable crystal orientation of Ni [1 1 1]∥Ag [1 1 1]∥GaN [0 0 0 2] at high deposition temperature. Auger electron spectroscopy profiles were used to examine the inter-diffusion of Ni/Ag atoms and Ga atoms in p-GaN, which led to the formation of a Ni/Ag–Ga alloy interface and the improvement of hole concentration in p-GaN. As a result, the chips' reliability and Ni/Ag-p-GaN contact characteristics were improved.