SPLITTING OF DEGENERACY OF VALENCE BAND IN STRAINED GAAS-LAYERS OBSERVED FROM POLARIZATION OF PHOTOELECTRONS

Eight specimens composed of a thin GaAs layer on top of a thick GaAsP layer were grown by metalorganic vapor phase epitaxy on GaAs substrates. The strain in the GaAs layers was estimated by X-ray diffraction, assuming that both the thick GaAsP layers and the substrates are free from strain. The release of the strain in the GaAs layers whose thicknesses are higher than the critical ones is realized and this results in dividing the layers into many subgrains. Some amount of strain still remains and deforms the subgrains. The rate of the release is described using the layer thickness normalized by the critical thickness. The remaining strains will split the degeneracy of the electron states in the valence band. The dependence of the amount of splitting on the strain was confirmed by the high spin polarization of photoelectrons.