Resonant and bound impurity states inn−GaSb(Se)from pressure dependence of Hall effect and resistivity at 77 K

Abstract

Hall-effect and resistivity measurements have been made on selenium-doped $n$-type GaSb in the temperature range between 1.4 and 300 K and at hydrostatic pressures up to \ensuremath{\sim}16 kbar. Samples with concentration in the range \ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}${10}^{16}$ to \ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ were investigated. The Hall coefficient behavior at 77 K has been analyzed in terms of ${\ensuremath{\Gamma}}_{1}$ and ${L}_{1}$ band conduction and two resonant states, ${E}_{\mathrm{Se}}^{{L}_{1}}$ and ${E}_{\mathrm{Se}}^{{X}_{1}}$, associated with the ${L}_{1}$ and ${X}_{1}$ conduction bands, respectively. For low-concentration samples, computer analyses give ${E}_{\mathrm{Se}}^{{L}_{1}}\ensuremath{-}{E}_{{\ensuremath{\Gamma}}_{1}}\ensuremath{\simeq}30$ meV and ${E}_{\mathrm{Se}}^{{X}_{1}}\ensuremath{-}{E}_{{\ensuremath{\Gamma}}_{1}}\ensuremath{\sim}65$ meV at 77 K and $P=0$; only the ${E}_{\mathrm{Se}}^{{X}_{1}}$ level is needed to explain the results for the highest-concentration sample. ${E}_{\mathrm{Se}}^{{L}_{1}}$ becomes a bound state at $3<P<4$ kbar, whereas the ${E}_{\mathrm{Se}}^{{X}_{1}}$ level becomes a bound state at $P>~5$ kbar, below the ${\ensuremath{\Gamma}}_{1}\ensuremath{-}{L}_{1}$ crossover at $P\ensuremath{\sim}8$ kbar; the high-pressure behavior is dominated by the ${E}_{\mathrm{Se}}^{{X}_{1}}$ level, as indicated by (a) Hall-coefficient and resistivity results at 77 K, (b) temperature-activated behavior above 77 K, and (c) nonsaturation effects in impurity-band conduction. The pressure dependence of the mobility at 77 K is analyzed in terms of ionized and neutral impurity scattering. The results indicate that neutral impurity scattering theory needs to be modified to account for (i) the nonhydrogenic nature of the selenium impurity center and (ii) the effects at high impurity densities.