Observation of Discrete Energy Levels by Tunneling Spectroscopy

Abstract

Tunneling spectrum observation was carried out on a Pb(Tl)Te film grown by hot-wall epitaxy method. The observed spectrum characteristics on Ag--SiO_x--Pb(Tl)Te junctions reflect a series of discrete energy levels E_n below the conduction band edge E_c, besides the quasi localized Tl impurity states in the valence band. These discrete energy levels E_n are well expressed by E_n-E_c=-1.6/n² (n: integer) in eV, and show quite a good consistency with the result by Esaki et al. Esaki From the investigation using the hydrogen-like ionization model, these donor-like deep centers seem to be realized only in such a highly degenerated p-type semiconductor with the minor n-type centers in the vicinity of surface region.