SUBSTRATE-TEMPERATURE DEPENDENCE OF THE MINORITY-CARRIER LIFETIME IN (ALGA)AS/GAAS MQWS GROWN WITH AS-2 AND AS-4

We report the results of measurement of the minority carrier properties 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 the same. We believe these lifetimes are determined by recombination via deep centres (possibly oxygen-related) close to the (AlGa)As/GaAs interface, though it is not easy to understand why the n and p-type lifetimes should be identical. For films grown with As2, the minority carrier lifetime is essentially independent of growth temperature, whereas with As4 the lifetime shows a maximum for films grown at about 675-degrees-C. This difference in behaviour explains earlier observation of the dependence of laser threshold current on growth temperature. The PL intensity does not simply relate to the measured lifetime, which suggests that surface morphology may play a significant role in determining the amount of light emitted.