We investigated theoretically the ordering-induced change of the ${\mathrm{E}}_1$, ${\mathrm{E}}_2$, and ${\mathrm{E}}_0^{\prime }$ transitions in ${\mathrm{Ga}}_{0.5}$${\mathrm{In}}_{0.5}$P using symmetry arguments and first-principles band-structure calculations. We show that upon (111) superlattice ordering these transitions are altered dramatically—some states shift up in energy, some shift down, and new “ordering-induced” transitions, absent in the disordered phase, now become allowed. Experimental observation of these changes could serve as new fingerprints of ordering. We have also studied the pressure dependence of the energies of the ${\mathrm{X}}_{1\mathrm{c}}$ and ${\mathrm{L}}_{1\mathrm{c}}$ derived states in the ordered superlattice. The recent experimental observation of the “${\mathrm{X}}_{1\mathrm{c}}$-like” state at higher pressure is identified as a mixture of the folded ${\mathrm{L}}_{1\mathrm{c}}$ and ${\mathrm{X}}_{1\mathrm{c}}$ states. A microscopic explanation is given.

• Received 8 November 1994

DOI:https://doi.org/10.1103/PhysRevB.51.13097