Shallow and thermally stable ohmic contacts to p-InAsP

We have investigated the electrical and metallurgical behavior of ohmic contacts to p- InAs0.80 P0.20. Auger depth profiling reveals that Ru, Ti, and V have better thermal stability against reaction than Pt, Pd, and Ni on p-InAsP. However, contacts with Pd deposited as the first layer exhibit lower specific contact resistances than contacts with Ti, V, Ni, Ru, or Pt as the first layer. For this reason, multilayer contacts were studied, adding Au as the top layer to minimize the metal sheet resistance. Transmission electron microscopy indicates that PdRuAu contacts aged for 3 days exhibit a uniform and shallow reaction with p-InAsP, with the Pd consuming only 4 nm of the semiconductor and the Ru serving as an effective diffusion barrier. Specific contact resistances of 3.8× 10-6 Ω cm2 as deposited and 1.7× 10-6 Ω cm2 for contacts aged at 250°C for 90 days in an evacuated quartz tube were measured for the PdRuAu contacts.