Spectroscopy of electron subband levels in an inversion layer on InSb

We report the observation of resonant transitions between electron subbands in an inversion layer on the surface of p-InSb. The transitions are excited with IR-radiation polarized parallel to the sample surface. This is possible because of the non-parabolicity of the surface subband structure. We compare the measured resonance positions with the results of a recent calculation by Arai et al. and find satisfactory agreement. In the light of both present experiments and theory we conclude that previously published photoconductivity work from Katayama et al. did not detect intersubband transitions.