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(3 nm)/Sb-doped SnO2 (ATO) (200 nm) ohmic contacts to p-GaN (5x10(17) cm(-3)). It is shown that the samples become ohmic with a specific contact resistance of 8.7x10(-5) Omega cm(2) upon annealing at 530 degreesC for 1 min in air. The oxidized contacts produce an extremely high light transmittance of 99% at a wavelength of 400 nm. The light-emitting diodes (LEDs) fabricated with the annealed Ag/ATO p-type contact layers give a forward-bias voltage of 3.42 V at injection current of 20 mA, which is better than that of LEDs with the most common oxidized Ni(5 nm)/Au(5 nm) contact layers. Based on scanning electron microscopy and x-ray photoemission spectroscopy results, the ohmic formation mechanisms are discussed. (C) 2004 American Institute of Physics.