Electrical Properties of Stannic Oxide Single Crystals

The Hall coefficient and electrical resistivity have been measured on single-crystal specimens of $n$-type Sn${\mathrm{O}}_2$ between 80 and 900°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×${10}^{16}$ and 5×${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ resulted in values of the "density-of-states" effective mass $m^{\mathrm{}\left(N\right)\mathrm{}}=0.22m$. 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 $m^{\mathrm{}\left(N\right)\mathrm{}}$ between 0.12 and $0.18m$. Antimony-doped crystals of Sn${\mathrm{O}}_2$ with $N_D>6\mathrm{}\times {10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$ appeared to be degenerate above 80°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°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 ${\Theta }_l\sim 500$°K.