Tunneling spectrum characteristic reflecting discrete energy levels in Pb(Tl)Te Films

Abstract

In order to directly detect the quasi localized Tl impurity states, tunneling spectrum observation has been carried out on PbTe films doped with a little amount of Tl impurity. As a result, Tl impurity states, QL1 and QL2 with energy intervals of 13–15 meV, are reproducibly observed, independently of the kinds of tunneling junctions and the samples with different amount of Tl impurity. Through the tunneling observations, a series of quasi localized states were observed besides the quasi localized Tl impurity states, and those energy levels E n are well expressed by E n — E c — 1.6/n 2 (eV) ( n; integer), which was once adopted by Esaki et al. to assign similar discrete levels detected on PbTe films. Here, the probable origins for observed discrete levels in this highly degenerated Pb(Tl)Te sample are discussed.