Tunneling spectroscopic analysis of optically active wide band-gap semiconductors

Tunneling spectroscopy has been used to detect the photoexcitation of charge carriers in the wide band-gap semiconductors, ZnO and cubic SiC. Because the process is energy sensitive, valence-to-conduction band or defect charge transfer transitions may be selectively excited and detected with the scanning tunneling microscope. Two types of transitions were detected which change the tunneling response; for cubic SiC valence-to-conduction band transitions were excited, while for Co2+ and Mn2+ doped ZnO electron charge transfer transitions from the dopants to the conduction bands occur. Preliminary results on the effect of a continuous energy (ultraviolet) light source on the tunneling spectrum of ZnO are presented.