OBSERVATION OF SPIN-SPLITTING CROSSING BETWEEN SUBBANDS IN THE OPTICALLY DETECTED CYCLOTRON-RESONANCE SPECTRA OF IN0.53GA0.47AS/IN0.52AL0.48AS HETEROJUNCTIONS

We present an investigation of the properties of a two-dimensional electron gas confined at an In0.53Ga0.47As/In0.52Al0.48As interface by optically detected cyclotron resonance (ODCR). ODCR spectra structured by quantum oscillations and subharmonic cyclotron resonances have been observed. Quite unexpectedly, the ODCR spectra also reveal a very strong and sharp peak with several fine structures. It is shown that this observation is due to the energy-level crossing of the spin splitting between the first and second subbands of the two-dimensional electron gas. The strong and sharp absorption is made possible only under conditions such that the energy separation of Landau levels is equal to the incident far-infrared photon energy, the Fermi energy lies in the center of a Landau level, and the uppermost occupied states of the two subbands have the same energy and spin. This behavior provides a precise determination of the effective mass and g factor.