Redistribution of constituent elements in Pd/Ge contacts to n-type GaAs using rapid thermal annealing

Abstract

Pd/Ge contact to n-type GaAs is performed by using electron-beam evaporation and rapid thermal annealing. The rapid thermal annealing is performed at 400–500 °C for various time durations. Low specific contact resistivity on the order of 10−6 Ω cm2 is obtained from measurements based on the transmission line model method. The contact depth profiles are analyzed by secondary ion mass spectrometry (SIMS). A very shallow ohmic contact is achieved. The redistribution of constituent elements after heat treatment is examined. A gallium SIMS signal bump is detected in the contact layer and is correlated with good ohmic contact behavior. A model based on Ga vacancies is proposed to explain this phenomenon. This shallow ohmic contact technology has been successfully utilized to fabricate GaAs/AlGaAs and GaAs/InGaAs/AlGaAs negative resistance field-effect transistors, for which shallow ohmic contact is critical.