Abstract
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.
Highlights
Epitaxial lift-off (ELO) and transfer of semiconductor structures from their growth substrates provides many advantages; allowing structures, grown lattice-matched on top of a high quality substrate, to be moved to substrates where the lattice mismatch would otherwise prevent high quality growth, or to those which would not be suitable for growth, e.g. flexible substrates.The investigation into stratified or layered devices, combining monolithically grown heterostructures and non-related bulk substrates, is an area of active research
In this report we demonstrate transfer of thin, II–VI selenide epitaxial films, following removal of the III–V substrate and buffer layers, from a temporary glass substrate onto target substrates of diamond and glass, while maintaining the structural integrity and surface quality
The release of II–VI multi-quantum well thin films based on ZnCdMgSe lattice-matched to InP has been achieved by complete removal of the InP substrate and InGaAs buffer layer
Summary
Epitaxial lift-off (ELO) and transfer of semiconductor structures from their growth substrates provides many advantages; allowing structures, grown lattice-matched on top of a high quality substrate, to be moved to substrates where the lattice mismatch would otherwise prevent high quality growth, or to those which would not be suitable for growth, e.g. flexible substrates. High quality DBRs have been achieved for material lattice-matched to GaAs through the use of superlattice structures to achieve higher refractive index contrast while maintaining growth quality [11,14] While this is possible for selenide material lattice-matched to InP, for optically-pumped devices the more flexible solution, proposed here, is to transfer the structures to separate mirrors or transparent substrates. An initial investigation into substrate removal of II–VI selenide structures with similar designs grown lattice-matched to InP was reported by Moug et al [20]; in that case the structures were adhered to glass using wax, and cracking or buckling of the II–VI material was observed This was attributed to strain in the epitaxial structure, despite the support of the adhesive, preventing further transfer of the structures. Building on previous reports of basic conversion of GaInN blue light emitting diodes to green, yellow and red [22], we are investigating the advantages of II–VI selenide colour conversion films for fast modulation speeds
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