The effects of chemical disorder on the electronic and optical properties of semiconductor alloy multilayers are studied based on the tight-binding theory and single-site coherent potential approximation. Due to the quantum confinement of the system, the electronic spectrum breaks into a set of subbands and the electronic density of states and hence the optical absorption spectrum become layer-dependent. We find that, the values of absorption depend on the alloy concentration, the strength of disorder, and the layer number. The absorption spectrum in all layers is broadened because of the influence of disorder and in the case of strong disorder regime, two optical absorption bands appear. In the process of absorption, most of the photon energy is absorbed by the interior layers of the system. The results may be useful for the development of optoelectronic nanodevices.

Optical absorption spectrum in disordered semiconductor multilayers

The effects of random distribution of magnetic impurities with concentration x in a semiconductor alloy multilayer at a paramagnetic temperature are investigated by means of coherent potential approximation and tight-binding model. The change in the electronic states and the optical absorption spectrum with x is calculated for weak and strong exchange interactions between carrier spins and localized spin moments on magnetic ions. We find that the density of states and optical absorption are strongly layer-dependent due to the quantum size effects. The electronic and optical spectra are broadened due to the spin fluctuations of magnetic ions and in the case of strong exchange interaction, an energy gap appears in both spectra. Furthermore, the interior layers show higher contribution in the optical absorption of the system. The results can be helpful for magneto-optical devices at a paramagnetic temperature.

Electronic and optical spectra in a diluted magnetic semiconductor multilayer

The effects of random distribution of magnetic impurities with concentration $x$ in a semiconductor alloy multilayer at a paramagnetic temperature are investigated by means of coherent potential approximation and tight-binding model. The change in the electronic states and the optical absorption spectrum with $x$ is calculated for weak and strong exchange interactions between carrier spins and localized spin moments on magnetic ions. We find that the density of states and optical absorption are strongly layer-dependent due to the quantum size effects. The electronic and optical spectra are broadened due to the spin fluctuations of magnetic ions and in the case of strong exchange interaction, an energy gap appears in both spectra. Furthermore, the interior layers show higher contribution in the optical absorption of the system. The results can be helpful for magneto-optical devices at a paramagnetic temperature.

We have theoretically studied the electronic and optical properties of a quantum well (QW) in which the well region is constructed from a binary alloy semiconductor A 1-x B x in the coherent potential approximation (CPA). A tight binding model is used for a single particle (electron, hole, Frenkel exciton) in the well composed by a rectangular array of N x x N y x N z sites. The effect of the diagonal randomness is reduced to the coherent potential Σ(E), which is assumed to be the same for all sites, and is selfconsistently determined with the average Green's function. For a slab (oo, ∞, N z ) and wire (∞, N y , N z ), the density of states?(E) is composed of N z (or N y x N z ) subbands, each shows the two (one)-dimensional van-Hove singularity. When x (or 1 - x) is small, a B (A) impurity-band always appears at the lower (higher) energy side of the lowest (highest) host-band. As the well width becomes narrower and/or the dimensionality decreases, the boundary for Δ/t decreases which separates the amalgamation type and the persistence type.

H. Kida

Papers

Electronic Structures of a Quantum Well of A1–xBx Alloy Semiconductor in the Coherent Potential Approximation