Chemical analysis of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures

Ohmic contacts to AlGaN/GaN heterostructures, which have low contact resistance and a good surface morphology, are required for the development of high temperature, high power and high frequency electronic devices. The paper presents the investigation of a Ti/Al based Ti/Al/Ni/Au ohmic contact to AlGaN/GaN heterostructures. Multilayer metallization of Ti/Al/Ni/Au was evaporated by an electron gun (titanium and nickel layers) and a resistance heater (aluminum and gold layers). The contacts were annealed by rapid thermal annealing (RTA) system in a nitrogen ambient atmosphere over the temperature range from 715 to 865 °C. The time of the annealing process was 60 seconds. The chemical analysis, formation and deterioration mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures were studied as a function of the annealing process conditions by a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS).