Interplay of alloying and ordering on the electronic structure of GaxIn1xP alloys

In this work, we extend the study of the electronic structure of disordered and ordered GaxIn1�xP alloys from the focus of most previous effort, x 0.5, to the whole composition range, 0x 1, using an improved empirical pseudopotential method with a supercell approach that employs a sufficiently large supercell size of 28 000 atoms—a size needed to realistically model disordered and partially ordered alloys. This study provides insights into the underlying physics of the alloy system in two important phases—disordered and CuPt ordered—and the interplay of alloying and ordering effects. It also offers much-needed guidance for the optimal use of ordering phenomenon in a range of applications including telecommunications, photovoltaics, and solid-state lighting. Critical-point energies, interband transition matrix elements, and optical anisotropy are calculated for both the disordered and ordered phases. The deviation of the wave function of an alloy state from that of a virtual-crystal state is analyzed using a spectral function. The implications of such deviation are examined explicitly for the above-mentioned properties. Unusual ordering effects are revealed in the indirectband-gap composition region of the alloy. The connection and distinction between the ordered and disordered structures are discussed. An often-used perturbation theory, known as “a quasicubic model,” is found to be reasonably accurate for predicting the anisotropy of the interband transition but inadequate for predicting the intensity variation with varying order parameter.