Highly transparent AgSn O2 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 Sn O2 (ATO) (200 nm) ohmic contacts to p-GaN (5× 1017 cm-3). It is shown that the samples become ohmic with a specific contact resistance of 8.7× 10-5 Ω cm2 upon annealing at 530 °C 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.