INVERSE-PHOTOEMISSION STUDY OF GE(100), SI(100), AND GAAS(100) - BULK BANDS AND SURFACE-STATES

We present momentum-resolved inverse-photoemission data from Ge(100)2 X 1, Si(100)2 X 1, and GaAs(100)4 X 2 surfaces. The bulk conduction bands of these three semiconductors are mapped along the GAMMAX direction. The following critical points are obtained (relative to the valence-band maximum): For Ge, L3c = 4.4 eV and L2c' = 7.8 eV; for Si, GAMMA15c = 3.05 ev, GAMMA2c' = 4.1 eV, and X1c = 1.25 eV; for GaAs, L3c = 5.45 eV and L1c = 8.6 eV. The L points are reached via surface umklapp processes. The experimental band dispersions and the critical points are consistent with state-of-the-art quasiparticle calculations. The empty pi* surface state is seen in Si and Ge. Its cross section changes significantly with the photon energy, reflecting a wave-function character derived from that of the bulk states near GAMMA.