OPTICAL SPECTROSCOPIC OBSERVATION OF SPONTANEOUS LONG-RANGE ORDERING IN ALGAINP

We report the unambiguous optical spectroscopic observation of spontan eous lang-range crystal ordering in AlGaInP epitaxial layers grown by metalorganic vapor phase epitaxy. Polarized spectroscopy demonstrates the existence of an in-plane anisotropy for samples grown on substrate s oriented close to (100). This anisotropy results from the order-indu ced splitting of the normally degenerate zone-center valence-band stat es. Our measurements allow the size of the valence-band splitting to b e measured and also allow a determination of the order-induced band-ga p reduction, Both of these quantities are found to decrease with incre asing misorientation of the substrate away from (100), indicating that the degree of ordering also decreases with increasing misorientation. (C) 1996 American Institute of Physics.