Low-temperature photoluminescence in AlxGa1−xAs grown by molecular beam epitaxy

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Abstract
We report the first observation of free exciton transitions (X), as well as donor and acceptor bound exciton transitions (D0X, D+X, and A0X), in the high‐resolution photoluminescence (PL) spectra of high‐quality AlxGa1−xAs layers grown by molecular beam epitaxy (MBE) over the composition range 0.01≤xxGa1−xAs samples of somewhat higher composition (x>0.2) in which only one or two bound exciton transitions have been reported together with the typically observed carbon free‐to‐bound transitions (e,A0). From a systematic study of MBE growth and PL spectral characterization, we find that both the free and bound exciton transitions of the AlxGa1−xAs layers correlate to their counterparts in high‐purity MBE GaAs layers and that their photon energies increase linearly with increasing x value, as expected for these low AlAs mole fraction samples. At compositions as low as 2.1%, and as high as 12.5%, spectral linewidths of D0X transitions were found to be as narrow as 0.3 and 2 meV, respectively, in reasonably good agreement with the recent PL linewidth predictions of Singh and Bajaj which are based on a theory of alloy scattering. These observations confirm the high quality of the low x‐value AlxGa1−xAs samples which were grown to thicknesses between 1 and 2 μm at substrate temperatures approaching 700 °C in a MBE system having low background impurity contamination.