Quantum well structures in cubic materials show benefits from intentional strain, due to splitting of the valence band. In hexagonal materials, the valence band shows similar splitting, but without the strain. We believe that, by doing Substrate Bandgap Engineering, hexagonal heterostructures can be made, with strong potential benefits for blue-green light emission. ZnMgSSe is used in all blue-green laser diodes that have attained RT CW operation. We invented and patented this composition, and grew it first in bulk form. This material is hexagonal at high Mg/Zn ratios. Hexagonal II-VI materials have. generally better crystalline structure than cubic materials, because they have no high temperature phase transitions and no twins. Thus, these materials are better substrates for epitaxial growth. Epilayers grown by MBE should be hexagonal on non-basal planes. Hexagonal II-VI materials show lower electron-beam laser thresholds than cubic ones; this correlates with efficient excitonic luminescence. Dislocation motion should be slower in hexagonal materials, thus reducing degradation. Optical storage, film marking, printing, photochemical fabrication, cell sorting in medical diagnostics, DNA fluorescence excitation (at the cellular level), COM (computer output to microfilm), pumping small dye lasers and specialized displays are some of the applications for these devices.
Keywords: bandgap engineering, wide bandgap, quantum wells, molecular beam epitaxy, zone melting, crystal grow
