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 -ty pe (AlGa)As-GaAs multi-quantum-well samples grown by molecular beam ep itaxy, as a function of growth temperature in the range 600 to 700-deg rees-C, using both As2 and As4. For equivalent growth conditions (subs trate 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 individua l sample there is a good correlation between the variations in lifetim e and external efficiency across a wafer, the variation being ascribed to temperature differences resulting from poor wetting with In. A muc h weaker correlation is observed from sample to sample, suggesting tha t there are factors other than the internal photoluminescence efficien cy that determine the light emitted from the surface. We tentatively s uggest that morphology may be a factor.