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2S/^11ZCZnSe crystals were grown by self-seeded physical vapor transport (PVT) technique in the horizontal configuration. The source materials were heat treated by H 2 reduction to remove the oxide followed by baking under dynamic vacuum to adjust the source composition toward that of congruent sublimation. Contactless growth of ZnSe single crystals have been performed consistently using three different source materials. The crystals grew away from the wall during the later stage of the growth with large (110) facets tend to align parallel to the gravity direction. The SEM micrographs and the ATM images showed that large (110) terraces and steps dominate the as-grown facets. The measured residual gas pressures in the processed ampoules agree well among various source materials and the major components were CO and H 2 . No preferred growth direction was found. The one-dimensional diffusion model on the mass flux of a multi-species PVT system was employed to analyze the conditions for contactless growth. The calculated thermal profile for supersaturation is very close to the thermal profile measured inside the empty furnace bore in the region of contactless growth. The effects of convective flows in the vapor phase inside the ampoule on the growth processes are discussed.

Promolecule radii have been calculated for nitride, oxide, and sulfide coordinated polyhedra with bond lengths fixed at the sums of effective ionic and crystal radii. Radii calculated for both nontransition and transition cations from the first four rows of the periodic table are highly correlated with crystal radii derived for oxide and sulfide crystals and with ionic radii derived for nitride crystals. Promolecule radii calculated for the coordination polyhedra in the minerals danburite, bromellite, and stishovite match experimentally determined bonded radii to within -0.02 A, on average, indicating that the position of the minimum in the electron density in the direction of a bond is governed in large part by the length of the bond and the electron density of the atoms that form the bond. Radii calculated for nitride, oxide, and sulfide anions correlate with bond type, tending to match ionic radii when bonded to highly electropositive cations and atomic radii when bonded to highly electronegative cations.

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Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe, and ZnSe1−xTex(0<x<0.4) grown by physical vapor transport. Energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. A best fit curve to the band gap versus composition x data gives a bowing parameter of 1.45. This number lies between the value of 1.23 determined previously on ZnSeTe bulk crystals and the value of 1.621 reported on ZnSeTe epilayers. Low-temperature photoluminescence (PL) spectra were measured on six samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe1−xTex samples, 0.09<x<0.39. For x=0.09, this emission energy is about 0.2 eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x=0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the exciton bound to Te clusters because of the high Te content in these samples.