Stimulated emission and optical gain in a single MOVPE-grown ${\mathrm{Zn}}_x{\mathrm{Cd}}_{1-x}\mathrm{S}\mathrm{e}-\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ quantum well

We have studied the stimulated emission from an optically pumped graded index separate confinement heterostructure, realized in the form of a metal-organic vapor-phase-epitaxy-grown single quantum well based on a wide-gap (ZnCd)Se semiconductor. The structure is composed of a central ${\mathrm{Zn}}_{0.78}{\mathrm{Cd}}_{0.22}\mathrm{Se}$ quantum well sandwiched between two thicker, zinc-rich (ZnCd)Se layers with a graded cadmium composition varying continuously and monotonously between 0% and 5%. The stimulated emission occurred at $\sim 2.49\mathrm{eV}$ $(T=8.5\mathrm{}\mathrm{K}),$ being spectrally redshifted with increasing temperature and disappearing for $T>~200\mathrm{K}.$ The optical gain has been measured using the variable stripe-length method, and values of the gain up to $620{\mathrm{cm}}^{\mathrm{-}1}$ have been achieved. High-resolution spectral studies of the stimulated emission have revealed a fine structure in the emission spectra originating from different localization sites for excitons. We identify the lasing mechanism as due to an inhomogeneously broadened system of localized excitons.