Abstract
Undoped Al <sub>x</sub> Ga <sub>1-x</sub> As epitaxial layers with 0≤x≤0.85 were grown on (100) GaAs substrates by liquid-phase epitaxy with a supercooling method. The growth rate, photoluminescent intensity and its full width at half maximum, and free-carrier concentration are also dependent on the AlAs solid composition of Al <sub>x</sub> Ga <sub>1-x</sub> As layers. The growth rate decreases rapidly with increasing AlAs solid composition. The 300 and 14 K photoluminescent spectra of high quality Al <sub>x</sub> Ga <sub>1-x</sub> As layers are presented. For the same growth conditions, both the free-carrier concentration and full width at half maximum of 14 K photoluminescent spectra have a minimum occurred at x≅0.4 due to the largest donor ionization energy value of residual donor impurities in the undoped epitaxial layers. The photoluminescence peak intensity is almost constant in the range of x<0.4, then drops quickly near x≅0.44, and keeps a weaker intensity beyond this AlAs solid composition. © 1989.