Internal Photoemission Measurements for the Determination of Schottky Barrier Height on a-Si, Ge:H, F Alloys

We report measurements of internal photoemission from Ni, Au, and Pd contacts into a-Si, Ge:H, F alloys. The alloys were prepared by d.c. glow discharge decomposition of either SiF4 or SiH4 and GeF4, and H2. The sharp exponential drop in subgap absorption in these alloys, measured by the Constant Photocurrent Method (CPM), allows the determination of barrier heights using internal photoemission thresholds. The barrier heights of Ni, Au and Pd contacts are presented as a function of alloy composition. We find Ni has the lowest barrier heights while Au shows the highest barrier heights over the entire range of Eopt. We also find that for the Ni and Au contacts, ΦB varies as 1/2 the optical gap. In the case of Pd, ΦB shows a dependence of 1/3 the optical gap. We observed an increase in ΦB for Pd contacts when etched with a diluted HF solution prior to metallization. A similar increase in ΦD was not observed for the Au and Ni contacts.