Highly transparent Ag∕SnO2 ohmic contact to p-type GaN for ultraviolet light-emitting diodes

We report on the formation of highly transparent and low-resistance Ag(3nm)∕Sb-doped SnO2 (ATO) (200nm) ohmic contacts to p-GaN (5×1017cm−3). It is shown that the samples become ohmic with a specific contact resistance of 8.7×10−5Ωcm2 upon annealing at 530°C for 1min in air. The oxidized contacts produce an extremely high light transmittance of 99% at a wavelength of 400nm. The light-emitting diodes (LEDs) fabricated with the annealed Ag/ATO p-type contact layers give a forward-bias voltage of 3.42V at injection current of 20mA, which is better than that of LEDs with the most common oxidized Ni(5nm)∕Au(5nm) contact layers. Based on scanning electron microscopy and x-ray photoemission spectroscopy results, the ohmic formation mechanisms are discussed.