ELECTROREFLECTANCE POLARIZATION STUDY OF VALENCE-BAND STATES IN ORDERED GA0.5IN0.5P

Anisotropic optical transitions in an ordered Ga0.5In0.5P alloy semico nductor have been studied by electroreflectance (ER) polarization spec troscopy. The atomic ordering of column-III sublattices causes a split ting of the valence-band maximum into two doubly degenerated levels at k=0. The ER spectra reveal signals originated from the GAMMA6c-GAMMA4 v, GAMMA5v and GAMMA6c-GAMMA6v transitions caused by the ordering. The [110) and [110BAR] ER signals due to the GAMMA6c-GAMMA6v transition s how strong anisotropic characters of their intensity and line shape. O n the other hand, the signal due to the GAMMA6c-GAMMA4v, GAMMA5v trans ition changes only in the intensity by the polarization direction. The ER intensities measured at various polarization angles follow the the oretically derived trends based on the selection rule for electronic-d ipole transitions in the ordered crystal.