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

In order to directly detect the quasi localized TI impurity states, tunneli ng spectrum observation has been carried out on PbTe films doped with a lit tle amount of Tl impurity. As a result, Tl impurity states, QL1 and QL2 wit h energy intervals of 13-15 meV, are reproducibly observed, independently o f the kinds of tunneling junctions and the samples with different amount of Tl impurity. Through the tunneling observations, a series of quasi localiz ed 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 discre te levels detected on PbTe films. Here, the probable origins for observed d iscrete levels in this highly degenerated Pb(Tl)Te sample are discussed. (C ) 1999 Elsevier Science S.A. All rights reserved.