Investigation of the photoluminescence and parameters of laser radiation generated by electron excitation of Al$_x$Ga$_{1-x}$As solid solutions

An investigation was made of the photoluminescence spectra and of the parameters of laser radiation generated by electron excitation of $n$- and $p$-type Al$_x$Ga$_{1-x}$As solid solutions with compositions in the range corresponding to the direct band structure. The nature of the composition dependences of the edge photoluminescence band intensity and of the threshold value of the electron current density obtained for the $n$-type solutions was attributed to the influence of the donor levels ($E_d=0.12$ eV) under the indirect $X_1$ minimum. It was found that the highest radiative recombination efficiency and the lowest threshold current density were exhibited by doped $n$-type films with $x\lesssim0.23$. In the case of compositions with $x\gtrsim0.23$ the highest efficiency and lowest thresholds were obtained for doped $p$-type samples. A study was made of the nature of the long-wavelength bands in the photoluminescence and stimulated emission spectra of the solid solutions. These bands were attributed to imperfections in epitaxial films resulting from an inhomogeneous distribution of Al.