Low-temperature photoluminescence excitation spectra are used to determine the order-dependent parameters: valence-band splitting and band-gap reduction in spontaneously ordered GaInP2. Effects due to composition fluctuations between different samples and the associated strain, as well as the excitonic binding energies, have been properly taken into account to yield accurate band-gap reduction and valence-band splitting values. The results from recently published ab initio band structure calculations are used to extrapolate the band-gap reduction from the strongest experimentally realized degree of ordering to perfect ordering. We find a total band-gap reduction of 471±12 meV, which is very close to recent theoretical predictions.

The optical properties of spontaneously ordered GaInPz grown by MOVPE are studied by means of photoluminescence, time-resolved photoluminescence, and polarization dependent photoluminescence excitation spectroscopy. Ordered samples grown on a substrate which is misoriented 6" toward [111]B show clear excitonic features both in luminescence and absorption. In excitation spectra both valence band edges are clearly resolved and are shown to be polarization dependent as predicted by band structure calculations. In these samples an additional non-excitonic low-energy photoluminescence emission is observed the peak energy of which depends strongly on excitation density and temperature and which shows extremely long luminescence lifetimes. A density of states model for ordered GaInP2 is proposed which allows to explain the results obtained in the last few years. The density of states model is discussed with respect to the microstructure of the ordered alloy as known from TEM investigations.

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Using dark-field transmission electron microscopy images of ordered GaInP samples, we show how the ordering domain size depends on the growth temperature. Samples with different average domain sizes are compared with regard to their photoluminescence ͑PL͒ and excitation spectra. We find a close correlation between the size of the ordered domains and the relative intensity of the PL peak from band-band recombination compared with the rapidly shifting, below-band-gap luminescence emission.