Observation of an atomlike energy spectrum with large g values by tunneling spectroscopy

We report the observation of localized energy levels in the forbidden gap of PbTe by tunneling spectroscopy in PbTe-Al2O3-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 n2 (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. © 1968 The American Physical Society.