Infrared reflectivity spectra and Raman spectra of Ga1−xAlxAs mixed crystals

Abstract

Thick layers of Ga_1−xAl_xAs with uniform composition were grown by an isothermal liquid‐phase epitaxial technique. Infrared reflectivity and Raman‐scattering spectra were measured with the same samples. The clean ’’two mode’’ behavior was confirmed in the reststrahlen band region, and the infrared reflectivity spectra were analyzed by using a Kramers‐Kronig dispersion relation and by curve fitting to two forms for the classical dielectric function, one an additive form and the other a factorized form. The experimental data are in good agreement with the calculated TO and LO frequencies, when the Chang‐Mitra model has been modified with the assumption of a nonlinear dependence of the oscillator strengths on composition. In the Raman spectra, the disorder‐activated LA mode near 200 cm⁻¹, a mode near 250 cm⁻¹, and a background‐level change were observed and attributed to atomic disorder. In the infrared reflectivity measurements the major disorder‐induced effect was the increase in the TO and LO damping constants.