FORMATION AND EVALUATION OF OHMIC CONTACTS TO GAAS BY ALLOYING TECHNIQUE

Abstract

Alloying is the most promising technique for making ohmic contacts on Gallium Arsenide. A simple, economical and reliable process for making ohmic contacts on GaAs by this technique has been developed. Some faeoiiities and fixtures required to, meet the specific needs of the process in the department were designed and established# Uniform thin coatings of Indium and Gold were evaporated on both pM and n-type GaAs for formation -of the ohmic contacts. The ideal proportion of In and Au was found to be 90 wt per-cent In and 10 wt peroent Au. Alloying was performed in vacuum at 5xi4P0R . at a constant temperature of 50000 for 30 seconds. Substrate temperature during evaporation was varied to find the optimum value. 3b demonstrate the effect of the ohmic contact thus formed,, contacts to GaAs were also made with Aluminium, and the results have been compared. Overall device resistance, symmetry of the current voltage characteristics and reproducibility have been examined. The resistance with Aluminium is lower than that without any fiLim on GaAs and is the lowest when In, Gold are alloyed, The contacts formed give the lowest contact resistance with 90 wt percent In and 10 wt percent .du, at a substrate temperature of 30000 and alloying temperature time cycle of 50000 for 30 seconds. The current voltage characteristics for the same contacts show linearity.