The room-temperature absorption spectra of low-temperature molecular-beam epitaxially grown samples were studied. Measurements were performed over an extended spectral range of photon energies, from 0.8 to 2.8eV. It was found that, in the case of as-grown low-temperature material, the absorption coefficients at the band gap were twice as high as those for high-temperature grown materials. Upon annealing the samples, a markedly reduced absorption coefficient was observed; both below and above the band gap. Absorption changes of up to 17000/cm for GaAs and 9000/cm for AlGaAs were observed, which occurred in 2 stages.

S.U.Dankowski, D.Streb, M.Ruff, P.Kiesel, M.Kneissl, B.Knüpfer, G.H.Döhler, U.D.Keil, C.B.Sørenson, A.K.Verma: Applied Physics Letters, 1996, 68[1], 37-9