Search for Photoinduced Dipoles at Heterojunction Interfaces

We tried to apply the mechanism of surface photovoltage (SPV) to a particular class of semiconductor heterojunctions, those having staggered gaps, with the aim of photoinducing charges of opposite sign at the interface notches and of creating a dipole that modifies the band discontinuities. We performed photoemission experiments at room temperature and at low temperature on the Si/InP(110) heterojunction for a thin coverage of silicon on n-doped and p-doped InP substrates. We found a shift of all the electronic features (both from Si and from InP) to higher binding energies at low temperature when using the n-type InP. No shifts were observed for p-type InP, where we expected to find a photoinduced interface dipole and a consequent shift in opposite directions of Si and InP structures. The implications of these results are discussed.