RESTRUCTURING OF THE ENERGY-SPECTRUM AND LIGHT-ABSORPTION IN A SEMICONDUCTOR IN AN INTENSE ELECTROMAGNETIC-FIELD

The two-band equation of Kane's model of a semiconductor is solved by the Bogoliubov-Mitropolskii method (1974) of averaging and the quasi-energy spectrum of electron-hole excitations in an intense electromagnetic field is investigated. The paramagnetic resonance case, when the frequency of the strong electromagnetic wave omega is close to the width of the energy gap of a semiconductor, is considered. According to the results obtained, the quasi-energy spectrum of electron-hole excitations depends significantly on the polarisation of the electromagnetic wave. In the case of circular polarisation the electromagnetic field removes the spin degeneracy of energy levels of free electrons and holes, one of the formed dispersion curves suffering discontinuity which leads under certain conditions to the appearance of a gap in the energy spectrum. In the case of linear polarisation the spin degeneracy is not removed but a gap in the spectrum also appears. In the most interesting case of elliptically polarised electromagnetic wave two energy gaps may be formed.