Exciton/free-carrier radiative emission ratio and temperature dependence of exciton lifetime for CdZnSSe/ZnSSe single quantum wells

摘要

Abstract: The time-integrated and time-resolved photoluminescence (PL) of Cd$-0.3$/Zn$-0.7$/S$-0.06$/Se$-0.94$//ZnS$-0.06$/Se$- 0.94$/ single quantum wells (QW) have been studied at various temperatures. The time-resolved PL is obtained by sum frequency conversion technique with 300 fs resolution. The PL line shape analysis based on a simple statistical model including both excitons and free-carriers showed that free exciton radiative recombination dominates the PL emission even at room temperature. However, free-carrier recombination contributed significantly to the emission spectrum down to 77 K. The free excitons are stable up to room temperature because of the large exciton binding energy and strong confinement of electrons and holes in these QWs. The free exciton decay time is approximately 300 ps at 130 K and it increases linearly to 1 ns at 295 K. This is the first time that exciton radiative recombination and linear temperature dependence of exciton lifetime is observed up to room temperatures for wide-gap II-VI QWs. This is due to the excellent quality of the samples and the strong confinement of electrons and holes in the QWs studied. This linear increase in exciton lifetime with temperature agrees with the theoretical prediction by considering the conservation of momentum requirement for radiative recombination for excitons in QW.!35