TRANSMISSION SCANNING-TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATION OF AU CR CONTACTS TO P-TYPE INP

The change in contact resistance produced by the annealing of Au/Cr metallizations to p-type InP has been correlated with the microstructural changes examined by electron microscopy. The contacts were initially non-ohmic. Their resistance decreased, but remained non-ohmic, even after annealing to temperatures up to 450 degree C. Transmission and scanning transmission electron microscopy of cross-section samples revealed the formation, at elevated temperatures, of CrP and AuIn intermetallic layers at the contact/semiconductor interface. Chromium appeared to initiate compound formation through the dissociation of InP, although gold likely assisted in driving the reactions. CrP formed first, at temperatures below 350 degree C, as a polycrystalline, fine-grained layer between the Cr and InP. The formation of islands of AuIn followed at about 400 degree C and these grew into a continuous layer upon further annealing.