Internal photoemission spectroscopy of semiconductor-insulator interfaces

Abstract

A review of the internal photoemission (IPE) (photoinjection) spectroscopy studies of the semiconductor-insulator (SI) interfaces is presented. While the conventional photoelectron spectroscopy represents a powerful tool for investigations of the initial stages of the interface formation, the IPE from the semiconductor into the insulator deals with the well-formed structures with a relatively thick top insulating layer (>10 nm) and seems to be a complementary technique for the structures used in electronic devices. Some techniques being employed in the photoemission can also be used in the IPE spectroscopy: the threshold spectroscopy and the yield spectroscopy. The first one provides a possibility of the interfacial barrier determination and the latter one can be used for the study of critical points of the electron band structure spectroscopy in the case of semiconductor emitter. The IPE into the insulator is used for the development of new techniques for the interface studies, including the hole injection into the insulator, the photoionization of the near interface states, the registration of the electron scattering and others. The characterization of the near-barrier insulator region is performed to determine the parameters of the insulator transition region. All these abilities of the IPE spectroscopy are described analytically and illustrated by the results of experimental study of the Si-SiO 2 interface as well as the Si-CaF 2 and the GaAs-(Ca, Sr)F 2 systems. The data available for other SI interfaces are reviewed too. The main attention is concentrated on the mechanisms of the interfacial barrier formation. The participation of both the interfacial dipoles and the weakly screened interfacial charges in the barrier evolution are demonstrated. As the result, the height of the interfacial barrier can be significantly changed when compared with that can be determined in the initial stages of the interface formation. On the other hand, these effects provide the possibility to change the barrier shape and height in a well controlled manner using appropriate technologies.