Investigation of Ni/Ag contact to p-GaN with an O ₂ plasma treatment and its application to GaN-based LEDs

In this paper, the contact structure of Ni-Ag/p-GaN with different O ₂ plasma treatment times for 1 and 5 min was utilized for investigation. From experimental results, the Ni-Ag contact to p-GaN with different O ₂ plasma treatment for 1 and 5 min reveals Schottky behaviors. Based on the variation of the specific contact resistance with respect to temperature, the dominant transport mechanism of Ni-Ag/p-GaN structure presented form thermionic emission to field emission as increasing time from 1 to 5 min. From the X-ray photoelectron spectroscopy (XPS) results, the increase of the N vacancies and antisite defects (O _N) would enhance the resistance of the treated p-GaN underneath the contact, which would make the Ni-Ag/p-GaN contact reveal Schottky behavior. With a 20 mA current injection, the operation voltage of light-emitting diodes (LEDs) with Ni/Ag contact to p-GaN through O ₂ plasma treatment 400 W-5 min was 3.13 V larger than the LEDs with Ni/Ag contact to p-GaN through O ₂ plasma treatment 400 W-1 min. This is due to the larger specific contact resistance. The 3.13 V operation voltage is still good and acceptable. Furthermore, the largest output power among all devices can be achieved. Besides, the reliability is still good.