Valence-band splitting due to symmetry breaking in long-range-ordered

{Ga}_{0.5}

{In}_{0.5}

P alloys grown on (001) GaAs by organometallic vapor-phase epitaxy has been systematically investigated with photoluminescence (PL) polarization spectroscopy. PL spectra measured along the [110] and [11¯0] directions showed anisotropy in both the peak energy and intensity together with a significant reduction of the peak energy. It has been found that the anisotropy in polarized PL spectra originates from the valence-band splitting between

Γ_{4 v}

Γ_{5 v}

, and

Γ_{6 v}

induced by symmetry breaking due to spontaneous CuPt-type long-range ordering of

{Ga}_{0.5}

{In}_{0.5}

P. On the basis of theoretical treatments of optical transition rates in the ordered crystal, a general formula describing the relative integrated intensity in PL polarization spectra has been obtained. According to this formula, the valence-band splitting energy has been estimated by measuring the temperature dependence of the polarized PL intensity. The correlations between the anisotropic PL and crystal-growth conditions such as growth temperature and gas-flow ratio in the input column-V and column-III sources are also discussed.

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