Alloy Clustering inAlxGa1−xAs-GaAs Quantum-Well Heterostructures

Data on spontaneous and stimulated emission, in the photon-energy range $E_g+5\mathrm{}\hslash {\omega }_{\mathrm{LO}}\gtrsim \hslash \omega \gtrsim E_g$, are presented on ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$-GaAs quantum-well heterostructures with ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ ($x\sim 0.4-0.5$) coupling barriers of size $L_B\sim 40-70$ Å and GaAs wells of size $L_z\sim 30-40$ Å. For $L_z$,$L_B\lesssim 50$ Å, Al-Ga disorder (clustering) in the alloy barriers is consistent with the observed spectral broadening and downward energy shift of the confined-particle transitions. A simple substitution of binary (AlAs) for ternary (AlGaAs) barriers eliminates alloy clustering and its effects, and makes unambiguous the identification of clustering in alloy barriers.