Stimulated emission and optical gain in II–VI semiconductor ZnCdSe/ZnCdMgSe multiple quantum well heterostructures

Steady-state and time-resolved photoluminescence (PL), stimulated emission, and optical gain characteristics of two molecular beam epitaxy-grown ZnCdSe/ZnCdMgSe multiple quantum well (MQW) heterostructures are presented. The samples were grown lattice-matched on semi-insulating InP (001) substrates with an InGaAs buffer layer grown after the removal of the native oxide surface layer. Each sample consists of four sets of QW heterostructures. Each set includes two 4-nm-thick ZnCdSe (bandgap ∼2.1 eV) QWs separated by a 10-nm-thick ZnCdMgSe (bandgap ∼2.7 eV) barrier layer. Adjacent sets are separated by a 100-nm-thick ZnCdMgSe layer. Both samples feature a 4-nm ZnCdSe cap and a 4-nm low-temperature ZnCdSe buffer at the interface of the II–VI and the III–V layers. One sample (sample A) has the 4-set MQW structure grown directly on the low-temperature buffer layer, while the other (sample B) has a 1-μm-thick ZnCdMgSe layer between the 4-period structure and the low-temperature buffer. The room-temperature PL spectra of sample A and sample B have peaks at 556 nm with PL lifetimes of 1.5 and 1.4 ns, respectively. Under intense ultrashort pulsed excitation, the edge-emitted PL exhibits substantial lifetime shortening and linewidth narrowing, which are indicative of stimulated emission. Optical gain measurements using the variable-stripe-length technique provided pump-intensity-dependent gain coefficients of 125–350 cm−1 for sample A and 167–478 cm−1 for sample B at 568 nm. The results demonstrate the ample potential of the heterostructures for realizing optically pumped lasers and other light emitters in the green-yellow spectral range.