Electronic and Optical Properties of Laterally Composition-Modulated AlxIn1-xAs, GaxIn1-xP, and GaxIn1-xAs Alloys

Results of a systematic study of the band structure and optical properties of laterally-composition-modulated semiconductor alloys AlxIn1-xAs, GaxIn1-xP, and Gaxin1-xAs are reported. [110] composition modulation occurs spontaneously during growth of (001) short-period superlattices or bulk epilayers of these alloys. The effect of this long-range lateral modulation is modeled using k.p theory andthe envelope-function approximation, while the vertical short-period superlattice is emulated by a uniaxial perturbation. We have studied the dependence of the electronic and optical properties of such structures on the modulation amplitude, profile, and negative feedback due to the coherency strain field. We find that (i) among the three-alloy systems, for a given modulation amplitude, thelargest band-gap reduction can be achieved in AlxIn1-xAs, and the smallest in GaxIn1-xAs, (ii) a step-function modulation gives a larger band-gap reduction that a sinusoidal modulation; (iii) when the coherency strain is tetragonal in the modulated direction, a strong in-plane optical anistropy is expected and when it is tetragonal in the growth direction, a weak in-plane optical anistropy isanticipated; (iv) the vertical short-period superlattice enhances the band-gap reduction, but reduces the in-plane optical anisotropy; and (v) the lateral composition modulation is inherently associated with a diminishing of the vertical short-period superlattice. The possibility and conditions of type-II band alignment in these modulated structures are discussed.