Cyclotron Resonance of Inversion Electrons on InSb

Abstract

Quasi two-dimensional electron systems as realized in space-charge layers on semiconductors have extensively been studied with spectroscopic methods on various materials in recent years.1 The most interesting feature on narrow-gap semiconductors like InSb or Hg1-xCdxTe is the coupling of valence and conduction band which results from their small gap energy. As a consequence the conduction band is strongly nonparabolic, i.e., the apparent mass strongly increases with energy. This behavior is well-known for three-dimensional narrow-gap semiconductors and also has been observed in two-dimensional systems of inversion or accumulation layers. In such systems the motion of electrons is restricted in one spatial dimension perpendicular to an interface by the action of the surface electric field. Due to the presence of this field new effects2 result from the interaction of electron states in the conduction band and hole states in the valence band: electrons in inversion layers can tunnel into the valence band. This effect leads to a resonant state, i.e., the electron in the inversion layer and the hole in the bulk are coupled.3,4 The subband energies are decreased as compared to parabolic semiconductors with large gaps. This effect has been studied experimentally with intersubband spectroscopy in accumulation layers on Hg1-xCdxTe.5 Excitation of intersubband resonances with light polarized parallel to the interface becomes possible as a result of a coupling between the free motion parallel to the interface and the quantized motion perpendicular to it. This has been demonstrated experimentally in inversion layers on InSb and InAs.6