OPTICAL BAND-GAP IN ORDERED GA0.5IN0.5P

Symmetry breaking effects on the top-most of the valence band in long- range ordered Ga0.5In0.5P have been investigated by means of reflectiv ity and photoluminescence spectroscopy. The results are consistent wit h a band scheme where the trigonal crystal field splits the valence ba nd in a high energy level of GAMMA6v, symmetry and a low energy level of GAMMA4v + GAMMA5v, symmetry. The corresponding optical transitions, GAMMA6v --> GAMMA6c and (GAMMA4 + GAMMA5)v --> GAMMA6c, are fairly we ll described in terms of trigonal selection rules.