Relaxation kinetics and photoluminescence lineshape of excitons in II-VI semiconductor quantum wells

Exciton localization by local potential fluctuations is studied theoretically and compared with energy- and time-resolved photoluminescence experiments under resonant excitation for MBE grown ZnCdSe/ZnSe and ZnSe/ZnMnSe samples. Within the exciton lifetime of about 100 ps a narrowing of the luminescence band and a shift of the maximum position to lower energies is seen. This relaxation is described by a kinetic equation for particles moving independently in a spatially correlated disordered potential. The resulting exciton distribution at low temperatures has strongly nonthermal character. Good quantitative agreement with experimental data is found. An approximately linear temperature dependence ofthe radiative lifetime is expected theoretically. The photoluminescence of a 2 nm ZnCdSe quantum well shows, indeed, an increase of the exciton lifetime from 80 ps (at 5 K) to 160 ps (at 40 K)