| Popis: |
Single crystals of silicon telluride, which has an unusual 2:3 stoichiometry, have been grown by a chemical vapor deposition technique. A photoluminescence level at 1.3 eV has been found as well as strong EPR signals, suggesting defects in the crystal which also could explain other unusual features. Thin films and bulk samples of silicon telluride glasses, ${\mathrm{Si}}_{x}{\mathrm{Te}}_{1\ensuremath{-}x}$, $0.02\ensuremath{\le}x\ensuremath{\le}0.25$, were prepared and examined by optical absorption, photoconductivity, infrared transmission, electrical conductivity, Hall effect, differential thermal analysis, EPR, and x-ray experiments. The values of the energy gap (0.7 to 1.0 eV), resistivity ($\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ \ensuremath{\Omega} cm), and glass transition temperature (120 to 175 \ifmmode^\circ\else\textdegree\fi{}C) were found to increase throughout the glass-forming region, with increasing silicon. Some microscopic structural features are shared by crystal and glass, including the presence of Si${\mathrm{Te}}_{4}$ tetrahedra, interatomic distances and reststrahlen absorption bands, even though the bonding seems to change from largely ionic in the crystal to largely covalent in the glasses. No EPR signal could be detected in the bulk glasses down to 77\ifmmode^\circ\else\textdegree\fi{}K. The Hall mobility of the glasses is approximately 1.0 ${\mathrm{cm}}^{2}$/V sec, independent of room temperature from 200 to 300 \ifmmode^\circ\else\textdegree\fi{}K, and indicates the predominance of hole conduction. No polaron effects are evident. Structurally, a covalent model consisting of tetravalent silicon and divalent tellurium is consistent with all the data for the amorphous system. |
