Direct-gap reduction and valence-band splitting of ordered indirect-gap AlInP2studied by dark-field spectroscopy

The order-dependent valence-band splitting and direct-gap reduction in spontaneously ordered indirect-gap AlIn${\mathrm{P}}_2$ are determined by dark-field spectroscopy at room temperature. Similar to direct-gap GaIn${\mathrm{P}}_2$ both parameters depend on the degree of long-range $\mathrm{Cu}{\mathrm{Pt}}_B$-type order. We obtain the direct gap for disordered and the order-induced changes of the spin-orbit splitting and the crystal-field splitting normalized to the direct-gap change for perfectly ordered AlIn${\mathrm{P}}_2$.