Solid solution, mass transport, and crystal growth studies of cadmium iron selenide

Cadmium iron selenide, a semimagnetic semiconductor, has been investigated. Solid solubilities of iron in CdSe were determined at temperatures between 650{dollar}spcirc{dollar}C and 1100{dollar}spcirc{dollar}C, using the X-ray diffraction Debye-Scherrer powder technique. The solubility limits of Fe in CdSe increase with the temperatures to reach a maximum of about 19.5 mole % FeSe{dollar}sb{lcub}1.24{rcub}{dollar} at 925{dollar}spcirc{dollar}C, and then decrease with further increasing temperature. Solidification phenomena of the Cd-Fe-Se solid solutions were observed employing optical microscopy, which reveals a typical divorced, eutectic type, nonequilibrium solidification. The combination of the X-ray diffraction and the microscopic investigations yielded a pseudo-binary, eutectic type phase diagram of the Cd-Fe-Se system.; Partial pressures of the major vapor species in the Cd-Fe-Se physical and the Cd-Fe-Se-Iodine chemical vapor transport systems were calculated. The partial pressure of gaseous iron species of the PVT system may be neglected compared to those of Cd and Se{dollar}sb2{dollar} species. This suggests that cadmium iron selenide crystals cannot be grown by the PVT method. For the PVT experiments, using the as-synthesized (CdSe){dollar}rmsb{lcub}0.90{rcub}(FeSesb{lcub}1.24{rcub})sb{lcub}0.10{rcub}{dollar} source materials, crystals with compositions of 6-8 mole % FeSe{dollar}sb{lcub}1.24{rcub}{dollar} were grown at a source temperature of 1000{dollar}spcirc{dollar}C and a {dollar}Delta{dollar}T of 12{dollar}spcirc{dollar}C. These result are contradictory to the thermodynamic predictions, and were further investigated employing specially purified source materials. Iron contents in the crystals grown in these experiments are close to zero. The transport of iron in the initial mass transport experiments may be due to the chemical impurities (most likely the metal chlorides) in the as-synthesized source materials.; Mass transport experiments of the Cd-Fe-Se-Iodine CVT system were performed as a function of source temperatures, the degrees of undercooling ({dollar}Delta{dollar}T), and initial iodine pressures. Promising parameters for the growth of cadmium iron selenide single crystals by the CVT method, e.g., the source temperatures of 800-850{dollar}spcirc{dollar}C, initial iodine pressures of 0.5-1.0 atm, and {dollar}Delta{dollar}T of 10-20{dollar}spcirc{dollar}C, were established. Mass fluxes of cadmium iron selenide were computed using a one-dimensional diffusion equation. The overall trends of the computed mass flux as a function of growth conditions are consistent with the experimental results. However, differences between the theoretical and experimental mass fluxes may be due to the uncertainties of the thermochemical data used and the approximations made in these estimations.; Single crystals of cadmium iron selenide with compositions of 6.5-8.5 mole % FeSe{dollar}sb{lcub}1.24{rcub}{dollar} and of about 5 mm edge lengths were successfully grown from the (CdSe){dollar}rmsb{lcub}0.90{rcub}(FeSesb{lcub}1.24{rcub})sb{lcub}0.10{rcub}{dollar} source materials by the CVT method. Compositions of various portions of the bulk crystals are nearly constant along its axis within the error limits, indicating that the crystals possess reasonable compositional uniformity. The indices of the crystal surfaces were obtained by the X-ray diffraction Laue method. The (0001) and (1011) planes usually developed as the natural facets on the surfaces, and (1010) and(1120) as the cleavage planes. A promising chemical etchant for cadmium iron selenide crystals was developed, consisting of about 20 vol. % concentrated HNO{dollar}sb3,{dollar} 60 vol. % glacial CH{dollar}sb3{dollar}COOH, and 20 vol. % concentrated H{dollar}rmsb2SOsb4{dollar} acids. Etch pit densities of the grown crystals are in the range of {dollar}5times10sp4{dollar}-{dollar}rm5times10sp5/cmsp2.{dollar}...