Sulfur passivation of AlxGa1−xAs for ohmic contact formation

Abstract

The use of sulfur to passivate Al0.3Ga0.7As surfaces to aid in the formation of Au and Al–Ni–Ge ohmic contacts has been studied using current–voltage measurements, Auger electron spectroscopy, and scanning electron microscopy (SEM). After cleaning the surfaces with solvents, the surfaces were passivated using (NH4)2S. The samples were exposed to laboratory air, then placed in a vacuum for evaporation of Au or Al–Ni–Ge. The samples were then analyzed as deposited or after heat treatment in forming gas at temperatures and times up to 500 °C and 30 min. Current–voltage measurements indicate that S passivation reduced the specific contact resistance for Au contacts but not for Al–Ni–Ge contacts. The Au films were stripped from the surface and SEM used to study the reaction ‘‘pits’’ on the Al0.3Ga0.7As surface. Presumably sulfur passivation assisted in ohmic contact formation with Au by preventing the formation of surface native oxides.