SURFACE DONORS INDUCED BY HYDROGEN AND CESIUM ABSORBED ON INP(110) SURFACES

The adsorption of Cs and H on n- and p-InP(110) surfaces at 170 K were studied by using a Kelvin probe (CPD) and ultraviolet photoemission spectroscopy (UPS). For p-InP it was found that both Cs and H induce surface Fermi-level pinning at about 1.3 eV above the valence-band maximum for low coverages and low exposures, respectively, while for n-InP the Fermi-level position within the band gap does not change as a function of coverage in both cases. This means that Cs as well as H are inducing surface states of donor type. These absorbates exhibit one s-valence-electron and the formation of adatom-induced surface donors may be understood in the surface-molecule picture. This model also suggests that both cesium and hydrogen are preferentially bound to surface indium atoms. The present study also shows that CPD combined with UPS is a very useful tool to measure surface band-bending. © 1990 IOP Publishing Ltd.