(111), (001) and (110) oriented CuInS2 films were grown epitaxially on H-te
rminated Si substrates by molecular beam epitaxy. The epilayers had surface
compositions in the range 0.27 < [In]/([Cu] + [In])(sf) < 0.63. Their elec
tronic and atomic surface structure were investigated by means of photoelec
tron spectroscopy and low energy electron diffraction (LEED). LEED pattern
symmetries of CuInS2(111)-(1 x 2). CuInS2(001)-(1 x 1), and CuInS2(110)-(1
x 1) were observed for near-stoichiometric films (cubic indices). Based upo
n simulations of LEED patterns, the origin of the CuInS2/Si(111)(cub)-(1 x
2) superstructure is attributed to a cation ordering of CuAu type in the fi
lm surface. For (110) oriented films, a complete faceting of the film surfa
ce into CuInS2(111) surface facets was found, independent of the surface co
mposition. A partial (111)-faceting was obtained for near-stoichiometric Cu
InS2/Si(001), which, however, could be suppressed under Cu-rich growth cond
itions. Usingvalence band spectroscopy, a clear signature of the (001) surf
ace was detected and is interpreted as due to a surface resonance. Ionizati
on energies and surface Fermi energies of differently oriented CuInS2 epila
yers were found to be non orientation dependent. For stoichiometric and Cu-
poor CuInS2 an electron affinity X of (4.9 +/- 0.15) eV was found, which is
distinctly higher than previously reported X values of CuInS. The electron
affinity decreases significantly with increasing Cu/In ratio in the film s
urface, down to similar to4.1 eV for [In]/([Cu] + [In])(sf) similar to 0.3.
The surface Fermi level of stoichiometric films is energetically located s
imilar to0.8 eV above the valence band edge. (C) 2001 Elsevier Science B.V.
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