Very Stable Ge/Au/Cr/Au Ohmic Contacts to GaAs

Abstract

The electrical and metallurgical annealing properties of Ge/Au/Cr/Au contacts have been studied on samples with different implantation doses. Especially the contacts with higher doses exhibit excellent thermal stability with low specific transfer resistance pt = 95 12~m. When they were annealed at 390~ for 128h, p~ was still as low as 140 t2~m. TEM cross sections of samples analyzed after a heat-treatment of 390~ revealed a smooth surface morphology and a smooth interface of the contact metal with the GaAs substrate. Taking into account thermochemical arguments the high thermal stability is attributed to the Au(Ga) solid solution formed during the alloying reaction. Current is found to flow from these Au(Ga) grains to the heavily Ge doped semiconductor interface via a tunneling mechanism according to the classical model. While the spreading resistance model is not applicable to the system under study the recent model of Dingfen et al.