Au-Be/Au and Au-Be/Cr/Au ohmic contacts to p-type InP and InGaAsP

A comparison of vacuum-deposited Au-Be/Au and Au-Be/Cr/Au metallisations, used for the preparation of ohmic contacts to p-type InP and InGaAsP, is presented. The electrical and metallurgical properties of such contacts were studied as a function of material parameters and of deposition and alloying conditions. The alloying temperature and time were found to be the important factors that strongly influence the contact properties. As a result, ohmic contacts to p-type InP and 1.3 mu m in InGaAsP (with N A -N D approximately=10 24 m -3 ) could be formed with the lowest values of specific contact resistance of about 3.5-4.5*10 -8 Omega m 2 and 2.5-3.0*10 -9 Omega m 2 respectively, at the optimum alloying conditions of 3 min at 420-430 degrees C. AES depth-composition profile measurements and SIMS surface analysis were used to study the thermally induced reactions at the metallisation-semiconductor interface accompanying the formation of ohmic contacts. The profiles obtained showed that a Cr layer incorporated between the thin Au-Be contact layer and a relatively thick Au top layer, acts as an effective barrier against the out-diffusion of phosphorus from the semiconductor and also against the migration of gold from the Au top layer into the semiconductor during the heat treatment of contacts.