Thermal stability of Ti/Pt/Au ohmic contacts on InAs graded InGaAs layers

Ohmic metals of Ti/Pt/Au metallization structure has been deposited onto n-type InAs/graded InGaAs layers. The nonalloyed specific contact resistance of 9.8 x 10(-7) Ohm m(2) is achieved. The thermal stability of the ohmic contacts was performed using rapid thermal annealing at various temperature. The associated specific contact resistance decreases with annealing temperature until 350 degrees C and then rapidly increases. The thermal stability can be achieved at least up to 350 degrees C. The degradation of the specific contact resistance at high annealing temperature is attributed to the decomposition of InAs and InGaAs materials. Auger electron spectroscopy depth profiles were performed to investigate the physical mechanism of contact formation of thermal stability during the annealing process. It was observed that the In atoms of the InAs layer diffuse out and penetrate into the Ti layer. In addition, the Ti atoms were slightly shifted into the InAs layer. The composition formation of Ti and In could be deduced. (C) 1998 Elsevier Science Ltd. All rights reserved.