Growth and optical characterization of indirect-gap AlxGa1-xAs alloys

Nonintentionally doped AlxGa1-xAs layers with 0.38 less than or equal to x less than or equal to 0.84 were grown on (100) GaAs substrates by liquid ph ase epitaxy (LPE) under near-equilibrium conditions. The crystalline qualit y of the samples was studied by photoluminescence at 2 K and room temperatu re Raman spectroscopy. The peculiar behavior in the photoluminescence inten sities of the indirect bound exciton line and the donor-acceptor pair trans ition is explained from the evolution of the silicon donor binding energy a ccording to the aluminum composition. It was also possible to observe the e xcitonic transition corresponding to the AlxGa1-xAs/GaAs interface, despite the disorder and other factors which are normally involved when growing hi gh-aluminum-content layers by this technique. Furthermore, Raman measuremen ts show the quadratic variations of longitudinal optical phonon frequencies with aluminum concentration in good agreement with previous experimental r esults. In this work we show that high quality indirect-gap AlxGa1-xAs samp les can be grown by LPE under near-equilibrium conditions. (C) 1999 America n Institute of Physics. [S0021-8979(99)00413-2].