Electrical Properties of Stannic Oxide Single Crystals

Abstract

The Hall coefficient and electrical resistivity have been measured on single-crystal specimens of $n$-type Sn${\mathrm{O}}_{2}$ between 80 and 900\ifmmode^\circ\else\textdegree\fi{}K. Data were obtained on samples in the "as grown" state, as well as on crystals which were thermally equilibrated in oxygen. A single-donor-level analysis on heat-treated crystals with donor concentrations (${N}_{D}$) between 1\ifmmode\times\else\texttimes\fi{}${10}^{16}$ and 5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ resulted in values of the "density-of-states" effective mass ${m}^{(N)}=0.22m$. Values of the donor ionization energy ${E}_{D}$ were found to decrease with increasing ${N}_{D}$. At infinite dilution ${E}_{D}$ has an estimated value of 0.15 eV. Room-temperature thermoelectric-power measurements resulted in calculated values of ${m}^{(N)}$ between 0.12 and $0.18m$. Antimony-doped crystals of Sn${\mathrm{O}}_{2}$ with ${N}_{D}>6\ifmmode\times\else\texttimes\fi{}{10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ appeared to be degenerate above 80\ifmmode^\circ\else\textdegree\fi{}K. The low-temperature Hall mobility was found to decrease with decreasing donor concentration. A qualitative treatment of the data appears consistent with the hypothesis of impurity-level transport. Mobility above 300\ifmmode^\circ\else\textdegree\fi{}K was analyzed by considering polar-optical modes of vibration as being the dominant lattice scattering mechanism. Both the perturbation and intermediate-coupling theories were in reasonable agreement with experimental values using a Debye temperature ${\ensuremath{\Theta}}_{l}\ensuremath{\sim}500$\ifmmode^\circ\else\textdegree\fi{}K.