DETERMINATION OF THE ANALYTICAL AND THE NON-ANALYTICAL PART OF THE EXCHANGE INTERACTION OF INP AND GAAS FROM POLARITON SPECTRA IN INTERMEDIATE MAGNETIC-FIELDS

The isotropic analytical exchange interaction a of GaAs and InP is determined to be 0.02±0.01 and 0.04±0.015 meV, respectively, for the two materials from a comparison of theoretically generated and experimentally determined transverse exciton energies and oscillator strengths in magnetic fields up to 20 T. The calculation of the theoretical spectra is based on a recent intermediate-field theory including the analytical and nonanalytical part of the exchange interaction. The experimental values are determined from a two-oscillator line-shape analysis of -,- +-, and -polarized magnetoreflection spectra. A newly developed model describing the exciton-free surface layer of a semiconductor by an exponentially decreasing damping of the exciton contribution to the dielectric constant is shown to improve strongly the quality of the line-shape fit. This improvement is achieved without increasing the number of fitting parameters as compared to the older model using a layer of finite thickness with infinite damping. From a similar comparison of theoretical and experimental values of the energies and oscillator strengths of longitudinal-transverse mixed-mode exciton spectra in magnetic fields which are found for the polarization in Voigt configuration (kH) the size of the nonanalytical exchange interaction LT in GaAs is determined to be 0.08±0.02 meV. For InP an upper limit of LT<~0.1 meV is derived. © 1979 The American Physical Society.