Influence of the miniband on emission mechanism in Zn1−xCdxSe/ZnSe quantum wells

Abstract

The stimulated emission has been investigated in Zn1−xCdxSe/ZnSe quantum wells with a constant sample width of 60 Å and barrier widths from 47 Å to 500 Å. A redshift of the stimulated emission peak with increasing excitation intensity was observed in samples with barrier widths narrower than 350 Å, and the stimulated emission mechanism in these samples is found to be dominated by exciton-exciton scattering. In contrast, no redshifts were observed for the sample with a barrier width of 500 Å, and the stimulated emission in this sample appears to be dominated by biexcitons. Time-resolved spectroscopy measurements were also performed on samples with barrier width of 47 and 500 Å below the threshold of stimulated emission, and it was found that the exciton lifetime decreases with increasing exciton energy for both of the samples. With a ten times smaller barrier width in the 47 Å sample, the lifetime of high energy exciton is significantly shorter than that of the other sample, while the low energy lifetime becomes longer. This implies that with a narrower barrier width of the quantum wells the excitons move faster to lower energy regions. The narrower the barrier, the easier it is for excitons to move through the miniband. This freedom of movement increases the exciton concentration at low energies in localized areas in the wells. High exciton concentration made exciton-exciton scattering more probable and reduce the stimulated emission threshold value.