EXCITON RELAXATION IN MOVPE GROWN ZNSEXTE1-X EPILAYERS

Exciton dynamics in ZnSexTe1-x epilayers (0 < x < 0.4) is studied thro ugh the emission decay kinetics at liquid helium temperature. At low S e concentration (x < 0.1) the emission contains free exciton lines and several impurity-related bands. The free exciton decay times in these samples are less than 100 ps due to the fast energy transfer to defec ts and the efficient migration of excitons into the interface region. The increase of Se content up to x approximately 0.2 causes gradual in crease of the exciton luminescence decay times (up to 1.5 ns) which ex hibits strong variation across the exciton emission band contour. This indicates the onset of exciton localization by the compositional fluc tuations of the mixed crystal.