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 propertie s 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 equival ent growth conditions (substrate temperature and arsenic species) the minority carrier lifetimes in n and p-type samples are the same. We be lieve these lifetimes are determined by recombination via deep centres (possibly oxygen-related) close to the (AlGa)As/GaAs interface, thoug h it is not easy to understand why the n and p-type lifetimes should b e identical. For films grown with As2, the minority carrier lifetime i s 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 do es not simply relate to the measured lifetime, which suggests that sur face morphology may play a significant role in determining the amount of light emitted.