Formation of metastable above-barrier hole states in ZnSe/BeTe type II heterostructures under high-density optical excitation

A considerable slowing down of the luminescence kinetics of the direct optical transitions has been discovered in ZnSe/BeTe type II heterostructures under high-density optical pumping by femtosecond laser pulses. The effect is attributed to the potential barrier that appears due to the strong band bending at a high density of spatially separated photoexcited carriers and forms a metastable above-barrier hole state in the ZnSe layer. This yields a longer energy relaxation time of the holes migrating to the adjacent BeTe layer. The experimental results agree well with the numerical calculations.