Optical absorption spectrum in disordered semiconductor multilayers

Abstract

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.Comment: 6 pages, 6 EPS figures, revised versio

Electronic and optical spectra in a diluted magnetic semiconductor multilayer

“…The results showed that, the photon absorption by the system is layer dependent and strongly changes by variation of the scattering-strength of the chemical impurities [21]. In the present study, we extend our previous approach [21] for the magnetic impurities at a paramagnetic temperature, and investigate the electronic and optical properties of DMS multilayers. To study the optical absorption spectrum in the presence of the magnetic impurities, we use the Onodera-Toyozawa theory [25], which is related to a binary mixed crystal or an alloy consisting of atoms (or molecules) A and B, in which the transition dipole moments of A and B atoms are equal.…”

“…With increasing x, the contribution of spin scattering by the localized spins in the scattering process of the carriers increases and the impurity band and hence, the whole electronic spectrum is broadened. This broadening which does not appear in LDOS of the NMS alloys [21] is a consequence of the localized spin fluctuation of magnetic impurities. It is evident that the strong exchange interaction splits the host band into two subbands.…”

“…Therefore, the type of disorder in our model is considered to be diagonal and accordingly, the off-diagonal disorder is outside of the scope of the present study. The random site energy u A,M r,n is assumed to be u A r,n and u M r,n with probabilities 1 − x and x when the lattice site (r, n) is occupied by the A and M atoms, respectively [21,26,27]. For A and M sites we have:…”

“…(6) In this equation, ℓ denotes the subband number (mode), k || is a wave vector parallel to the layer, and the integral is taken over all the wave vectors in the first Brillouin zone (1BZ) of the two-dimensional lattice [21]. G 0 n,n ′ (ℓ, k ) is the mixed Bloch-Wannier representation of G 0 which can be expressed as…”

“…In previous studies [21][22][23], by applying the single-site coherent potential approximation (CPA) [24] to semiconductor alloy multilayers, the effects of chemical (nonmagnetic) disorder on optical absorption spectrum were investigated. The results showed that, the photon absorption by the system is layer dependent and strongly changes by variation of the scattering-strength of the chemical impurities [21]. In the present study, we extend our previous approach [21] for the magnetic impurities at a paramagnetic temperature, and investigate the electronic and optical properties of DMS multilayers.…”