The Effect of Al and Pt/Ti Simultaneously Annealing on Electrical Characteristics of n-GaN Schottky Diode

Wideband gap semiconductor GaN has received increasing attention for its potential for wide variety of high-power, high- performance switching and high-frequency devices application. In this paper the simultaneous annealing effect at a temperature of 400degC ~700degC in N₂ ambient for 12 min on aluminum (1500 Adeg) as an ohmic contact while Pt/Ti (700 Adeg/700 Adeg) bilayer as a Schottky contact on the electrical characteristics of n- GaN Schottky diode was investigated. It was found that at a annealing temperature of 400degC produced the best (I-V) characteristics, barrier height (Phi_B) 1.1 eV, ideality factor (eta) 1.1 as compared to the other annealing temperature. The (C-V) characteristics of n-GaN Schottky diode were measured at 100 kHz and 1 MHz frequency at different annealing temperature. It was found that at annealing temperature of 400degC, the depletion region is maximum with the capacitance value varied from 0.02 pF ~ 0.04 pF. At low frequency 100 kHz the capacitance increase with increasing forward voltage which is frequency independent, while at high frequency 1 MHz the capacitance- voltage curve is almost flat. The surface morphology of n-GaN Schottky diode before annealing and after annealing was observed by SEM, XRD. It was found that Al (1500 Adeg) didn´t show any significant loss of dimensional stability at annealing temperature 400degC~700degC, while Pt/Ti (700 Adeg/700/Adeg) show balling effect, surface morphology degradation at above 400degC which was confirmed by XRD measurement. Hence we conclude that rectifying behavior of n-GaN Schottky diode was observed at annealing temperature 400deg C while annealing at above 400degC~700degC the rectifying characteristics of n-GaN Schottky diode changed to ohmic behavior due to Pt/Ti (700 Adeg/700 Adeg) island form of surface morphology occurred, while Al (1500 Adeg) as a ohmic contact show thermal stability at high temperature annealing above 400degC of n-GaN Schottky diode.