GAS-SOURCE MOLECULAR-BEAM EPITAXY GROWTH OF ZNSE ON NOVEL BUFFER LAYERS

Thin films of ZnSe on pseudomorphic and partially relaxed (In,Ga)P buf fer layers (on GaAs) have been examined; both epilayers were grown by gas source molecular beam epitaxy. The ZnSe layers were grown using el emental Zn and thermally decomposed H2Se. The II-VI nucleation occurre d following an ex situ transfer in air of the As-passivated (In,Ga)P b uffer layers, grown using In, Ga, and cracked PH3. Microstructural cha racterization of the II-VI/III-V heterostructures was performed with h igh-resolution x-ray diffraction and transmission electron microscopy. The (511) reflection of the x-ray rocking curves was used to measure the residual strain in the ZnSe/(In,Ga)P/GaAs structures, and to deter mine the alloy composition of the (In,Ga)P. The (400) reflection of th e x-ray diffraction rocking curves indicated peaks having full width a t half-maximum of 130 and 18 arcsec for the relaxed ZnSe on thin (1 mu m) pseudomorphic (In,Ga)P buffer layers, respectively. Transmission el ectron microscopy confirmed the relaxed or pseudomorphic nature of eac h heterolayer. Thicker (>4 mum) In0.52Ga0.48P buffer layers were still not completely relaxed, and exhibited a residual lattice mismatch of approximately 0.11% between the ZnSe layer and the In0.52Ga0A8P buffer layer. Relatively thick (1-2 mum) ZnSe films had surface morphologies that were featureless when examined by Nomarski microscopy and scanni ng electron microscopy. Low-temperature photoluminescence spectra orig inating from the ZnSe films on the partially relaxed (In,Ga)P buffer l ayers were dominated by donor-bound and free-excitonic features with e ach exhibiting nearly the same intensity. Luminescence from extended d efects (the Y0 and I(upsilon) transitions) within the ZnSe layer, and luminescence originating from the (In,Ga)P buffer layers, were also ob served.