EXCITONS IN INDIRECT-GAP ALXGA1-XAS

We have studied unintentionally and deliberately Si- or Mg-doped indir ect-gap AlxGa1-xAs (0.38 less-than-or-equal-to x less-than-or-equal-to 0.835) prepared by a variety of growth techniques, by means of photol uminescence in the temperature range 4.2 K less-than-or-equal-to T les s-than-or-equal-to 300 K. At 4.2 K two high-energy transitions were de termined to be due to the radiative decay of donor and acceptor bound excitons. The zero-phonon bound exciton transitions are accompanied by phonon replicas due to the emission of one or two AlAs- or GaAs-like phonons. The peak energy of the indirect donor bound exciton increases in the range 0 less-than-or-equal-to x less-than-or-equal-to 1 corres ponding to the relation (T less-than-or-equal-to 30 K) hv(c)(D0X, x) = 1.9690 + 0.1975x + 0.0517x7.4 (in eV). The Al content was determined by electron beam microanalysis using different standards. The donor bo und exciton binding energy was estimated using the intensity quenching versus the temperature. Including these values the indirect gap-compo sition relation is given. The direct-indirect crossover point was dete rmined in excellent agreement with earlier estimations. Besides the ra diative decay of bound excitons free exciton recombination was observe d at elevated temperatures.