E1, E2, and E0' transitions and pressure dependence in ordered Ga0.5In0.5P

We investigated theoretically the ordering-induced change of the E1, E2, and E0' transitions in Ga0.5In0.5P 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 X1c and L1c derived states in the ordered superlattice. The recent experimental observation of the ''X1c-like'' state at higher pressure is identified as a mixture of the folded L1c and X1c states. A microscopic explanation is given