Width of the excitonic absorption line in Al x Ga1 − x as alloys

Abstract

Experimental data on the width of the absorption line corresponding to the exciton ground state in high-quality samples of AlxGa1 − xAs (x = 0.15) quasi-binary alloy, obtained by Seisyan et al. (2005), are analyzed. The line corresponding to the 1s state is divided into separate components taking into account strain-induced splitting; Lorentzian- and Gaussian-shape contributions to the absorption curve; and overlap with the continuum absorption band, which broadens with increasing temperature. Analysis of the integrated absorption, relying on the fact that the temperature dependence of the absorption is typical of exciton polaritons in media possessing spatial dispersion, was carried out with the following parameters: critical value of the dissipation damping of the exciton Γc = 0.32 meV and maximum value of the absorption coefficient Kmax = 89.5 eV/cm. This analysis makes it possible to determine the homogeneous component of the line broadening, which, up to the critical temperature Tc = 155 K does not exceed 0.2 meV. It is found that the “natural” width of the 1s-exciton line does not exceed 2.6 meV at T = 1.7 K, which is in agreement with theoretical estimates. At T = 1.7–60 K, the inhomogeneous broadening of the exciton peak related to the exciton scattering and localization by fluctuations of the alloy composition exceeds contributions related to phonons and ionized impurities by more than an order of magnitude and is dominant, but does not affect the integrated absorption by excitonic polaritons.