Zinc Selenide exhibits some extremely attractive properties for development as the next generation orientation-patterned semiconductor for mid-infrared frequency conversion. These include a high nonlinear figure of merit (d2/n3 =198), an extremely wide transparency range (0.48-22m), low dispersion (which favors large grating periods and wide spectral acceptance bandwidth), and very low absorption losses. A primary obstacle to producing OP-ZnSe, however, has been the lack of availability of ZnSe single crystals. Extensive efforts to develop melt growth of ZnSe crystals in the late 1990s were abandoned due to severe twinning problems and the replacement of potential ZnSe blue-green diodes with the advent of GaN.
The objective of this work, therefore, was to revisit physical vapor transport growth of single crystal ZnSe. Optical-grade polycrystalline ZnSe starting material was vacuum-encapsulated in 13-mm I.D. heavy-walled quartz ampoules, and preliminary unseeded growth was performed using using controlled temperature gradients in horizontal transparent furnaces, which yielded high-optical-quality, cubic centimeter-sized, randomly-oriented single crystals. We further evaluated seeded growth on lattice-matched (100), 4°-offcut GaAs substrates as well as on orientation-patterned GaAs templates. Detailed characterization of ZnSe epitaxial growth quality and quasi-phase matched grating propagation will be reported.