XPS study on the change of surface potential of GaSe and InSe induced by Ar+ sputtering

The changes of surface potential, directly induced by Ar ion sputtering, have been studied using X-ray photoelectron spectroscopy for both p-type GaSe and n-type InSe with no dangling bonds on the cleaved surface. Since the sputtering makes the surface metal-rich in these compounds, it is then predicted that the surface potential dramatically changes. The change of work function due to sputtering is obtained by measuring the emission spectrum of slow secondary electrons. It decreases from 5.7 eV to 5.3 eV in GaSe and increases from 4.5 eV to 5.0 eV in InSe. The magnitude of band bending due to sputtering is estimated from the shift of core levels. It is found that the band bends downwards by about 0.2 eV in GaSe and upwards by about 0.6 eV in InSe. These experimental results are explained in terms of the thin metallic layer and the interface states on the sputtered surface.