SHALLOW OHMIC CONTACT TO BOTH N-GAAS AND P-GAAS

A shallow Pd/Ge/Ti/Pt/ohmic contact for both n- and p-GaAs has been investigated. The contacts were rapid thermally annealed in N2 for 15 s at temperatures from 350 to 550-degrees-C. The lowest average specific contact resistances were 4.7 X 10(-7) and 6.4 X 10(-7) OMEGA cm2 for the n- and p-GaAs, respectively, when the n-GaAs was doped with Si to 2 X 10(18) cm-3 and the p-GaAs was doped with carbon to 5 X 10(19) cm-3. Electrical measurements and Auger depth profiles showed that the contacts were stable as they remained ohmic after an anneal at 300-degrees-C for 20 h for both n- and p-GaAs. The p contact is more stable than the n contact at the higher temperatures where there is more As outdiffusion as determined by Auger depth profiles. Transmission electron microscopy showed that the interfaces between the p-GaAs and the contacts were smooth for both as-grown and annealed samples, and no oxides were detected.