The two-dimensional electron gas adjacent to the grain boundary in a bicrystal of the narrow-gap semiconductor p-type ${\mathrm{Hg}}_{0.79}$${\mathrm{Cd}}_{0.19}$${\mathrm{Mn}}_{0.02}$Te has been studied by means of cyclotron-resonance measurements in the mega-Gauss field range with ${\mathrm{CO}}_2$ and CO laser radiation sources. Under these conditions, the resonance energies are larger than both the depth of the confining potential well and the band-gap energy. For a photon energy of ħω=120 meV a pronounced single resonance line is observed at 23 T. The corresponding cyclotron effective mass exhibits a strong nonparabolicity—it increases about three times between 23 and 100 T, in agreement with the results of our self-consistent band-structure computations. Measurements in tilted magnetic fields reveal a lack of the angular dependence of the resonance field. The resonance linewidth at 23 T is larger by a factor of 7 than that evaluated from low-field transport data. This is interpreted as a result of the degeneracy of the first excited Landau level with the quasicontinuum of higher subband levels. In addition, the linewidth exhibits an abrupt increase in the magnetic-field range between 20 and 30 T. This is discussed in terms of two possible mechanisms: one is the magnetic-field-induced transfer of electrons into the ground-state subband, which is charcterized by efficient scattering of electrons by grain boundary defects; the other is the magnetic-field-induced localization of the two-dimensional electron gas at the grain boundary.

• Received 20 July 1995

DOI:https://doi.org/10.1103/PhysRevB.52.16588