Observation of an Atomlike Energy Spectrum with LargegValues by Tunneling Spectroscopy

We report the observation of localized energy levels in the forbidden gap of PbTe by tunneling spectroscopy in PbTe-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$-metal junctions. This study reveals the existence of deep centers in the neighborhood of the PbTe surface, in which the energies of major levels are approximately inversely proportional to $n^2$ ($n$ an integer, ≥3). Many of the levels show enormously large $g$ values (up to 18), which seem to suggest a mixing of these localized states with the bands in PbTe.