EXTERNAL PHOTOLUMINESCENCE EFFICIENCY AND MINORITY-CARRIER LIFETIME OF (AL,GA)AS/GAAS MULTI-QUANTUM-WELL SAMPLES GROWN BY MOLECULAR-BEAM EPITAXY USING BOTH AS2 AND AS4

We report the results of measurement of the external photoluminescence efficiency and minority carrier lifetime of a series of n - and p -type (AlGa)As-GaAs multi-quantum-well samples grown by molecular beam epitaxy, as a function of growth temperature in the range 600 to 700-degrees-C, using both As2 and As4. For equivalent growth conditions (substrate temperature and arsenic species) the minority carrier lifetimes in n- and p-type samples are found to be the same. We suggest that the lifetimes are determined by recombination via deep centers (possibly oxygen-related) close to the (AlGa)As/GaAs interface. For an individual sample there is a good correlation between the variations in lifetime and external efficiency across a wafer, the variation being ascribed to temperature differences resulting from poor wetting with In. A much weaker correlation is observed from sample to sample, suggesting that there are factors other than the internal photoluminescence efficiency that determine the light emitted from the surface. We tentatively suggest that morphology may be a factor.