Optimization of ohmic contact for the fabrication of InGaN/GaN multiple quantum well blue LED

A 'p-contact first' process flow for InGaN/GaN LED with Al as n-contact and Ni/Au as p-contact resulted in high series resistance due to degradation in p-contact resistance during subsequent thermal processing steps. However, in order to adopt an 'n-contact first' process, it is necessary to develop a contact metallization scheme for n-GaN, which can withstand annealing in oxygen ambient, necessary for activation of p-contact. Al/Au, Ti/Al and Ti/Al/Au are studied as possible alternatives to Al for n-contact. It is found that Al/Au, Ti/Al and Ti/Al/Au contact results in lower contact resistance than Al alone contact. Thermal stability and immunity to oxidizing ambient for these contacts is studied by subjecting the samples to oxidizing ambient in the temperature range of 550 - 700°C. While Ti/Al contact results in the lowest contact resistivity, it suffers from poor thermal stability. The contact resistance with Ti/Al/Au contact is comparable to Ti/Al. Ti/Al/Au also offers good thermal stability and immunity to oxidizing ambient. Thus use of Ti/Al/Au allows the use of 'n-contact first' process that is expected to improve the series resistance of the device and hence the efficiency of LEDs. © 2012 SPIE.