IN OVERLAYERS ON SB PASSIVATED GAAS

Photoemission spectroscopy has been performed on Sb/GaAs. We have shown that Sb/nGaAs returns to near flatband (approximately 0.3 eV below the conduction-band minimum) upon annealing. This is in contrast to previous results which demonstrated this behavior on p type (movement to approximately 0.1 eV above the valence-band maximum) but not on n-type substrates [F. Schaffler, R. Ludeke, A. Taleb-ibrahimi, G. Huges, and D. Rieger, J. Vac. Sci. Technol. B 5, 1048 (1987); R. Cao, K. Miyano, T. Kendelewicz, 1. Lindau, and W. E. Spicer, Surf. Sci. 206, 413 (1988)] and in agreement with the results of Zahn et al. [T. Zahn, Technische Universitat Berlin (private communication)] showing analogous behavior in n-type GaAs. Indium overlayers have been deposited on these surfaces and band bending, chemistry and overlayer morphology have been studied. Analysis of Ga (3d) and As (3d) spectra indicate' that much stronger clustering is observed on p-type than on n-type substrates. Consistent with this assertion is that stronger chemistry is observed on n-type substrates as is evident from the In (4d) and Sb (4d) spectra. The fact that the same clustering behavior is observed for In/GaAs for both n- and p-type substrates suggests that the Sb interlayer is primarily responsible for the inequivalent clustering observed. Band bending results indicate that for Sb passivated substrates the Fermi-level pins at 0.6 and 0.4 eV as opposed to 0.75 and 0.5 eV above the VBM for n and p-type GaAs on the unpassivated surface.