Processing and characterisation of II–VI ZnCdMgSe thin film gain structures

Lattice-matched II–VI selenide quantum well (QW) structures grown on InP substrates can be designed for emission throughout the visible spectrum. InP has, however, strong visible-light absorption, so that a method for epitaxial lift-off and transfer to transparent substrates is desirable for vertically-integrated devices. We have designed and grown, via molecular beam epitaxy, ZnCdSe/ZnCdMgSe multi-QW gain regions for vertical emission, with the QWs positioned for resonant periodic gain. The release of the 2.7μm-thick ZnCdSe/ZnCdMgSe multi-QW film is achieved via selective wet etching of the substrate and buffer layers leaving only the epitaxial layers, which are subsequently transferred to transparent substrates, including glass and thermally-conductive diamond. Post-transfer properties are investigated, with power and temperature-dependent surface- and edge-emitting photoluminescence measurements demonstrating no observable strain relaxation effects or significant shift in comparison to unprocessed samples. The temperature dependent QW emission shift is found experimentally to be 0.13nm/K. Samples capillary-bonded epitaxial-side to glass exhibited a 6nm redshift under optical pumping of up to 35mW at 405nm, corresponding to a 46K temperature increase in the pumped region; whereas those bonded to diamond exhibited no shift in QW emission, and thus efficient transfer of the heat from the pumped region. Atomic force microscopy analysis of the etched surface reveals a root-mean-square roughness of 3.6nm. High quality optical interfaces are required to establish a good thermal and optical contact for high power optically pumped laser applications. •ZnCdSe/ZnCdMgSe II–VI multi-quantum well active regions are grown on InP.•Free-standing, II–VI films removed from InP substrate and InGaAs via wet etching•Negligible change of the quantum well photoluminescence after substrate removal•II–VI film transferred to diamond shows good thermal contact/performance.