Cross-sectional TEM of Pd/InP and Au/InP interfaces formed at substrate temperatures near 300 and 77K

Depositing Pd or Au on InP at cryogenic substrate temperatures has previously been found to significantly increase the barrier height of the resulting Schottky diode. In this work, cross-sectional transmission electron microscopy was used to determine the structural differences between metal/semiconductor (MS) interfaces formed at 300K (RT) and at 77K (LT). In the Pd/InP case, RT samples exhibited a thick amorphous interaction layer at the MS interface, while LT samples only had a thin phosphorous-rich interfacial layer. However, in the Au/InP case, no amorphous interlayers were observed in any of the samples. Instead, a small amount of Au was found to extend into the InP lattice in the RT case which was not present in LT samples. The thermal stability of the barrier height was studied as well. LT Au/InP samples were found to exhibit a distinct barrier height shift when annealed at 200 degrees C which was linked to a grain coarsening in the polycrystalline Au layer at this temperature. X-ray diffraction was used to verify changes in the polycrystalline metal's average grain size. We conclude that a significant reduction in the interaction between the deposited metal and InP was responsible for the greatly enhanced barrier height observed in LT interfaces.