Weak-Field Magnetoresistance inn-Type Aluminum Antimonide

Abstract

Galvanomagnetic measurements have been carried out on a number of single-crystal samples of $n$-AlSb(Te), with room-temperature carrier concentrations between 5×${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and 2.5×${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The measurements were carried out over the temperature range 77 to 500°K. An impurity activation energy, extrapolated to 0°K, of 0.068 eV is obtained from the Hall data. Above 250°K, the temperature dependence of the Hall mobility is proportional to $T^{-1.8\mathrm{}}$. Magnetoresistance measurements were performed at fixed temperatures in the range 77 to 295°K. The magnetoresistance was found to be proportional to $H^2$ up to at least 30 kG. The relations between the various magnetoresistance coefficients follow very closely those required for a [100] multivalley conduction band. The anisotropy parameter $K=\left(\frac{m_{\mathrm{II}}}{m_{\perp }}\right)\left(\frac{{\tau }_{\perp }}{{\tau }_{\mathrm{II}}}\right)$ is found to be ∼7 at room temperature in the sample of lowest carrier concentration (where the $m\text{'}\mathrm{s}$ are the effective masses and the $\tau \text{'}\mathrm{s}$ the relaxation times referred to directions parallel and perpendicular to the unique axis of a spheroidal surface of constant energy). This value decreases to ∼3 at 77°K, suggesting increasing anisotropy of scattering due to ionized impurities. An argument is presented in favor of the prolateness of the ellipsoids. Assuming $\frac{{\tau }_{\mathrm{II}}}{{\tau }_{\perp }}=1\mathrm{}$, $K=7\mathrm{}$, six valleys, and a conductivity effective mass of $0.30m_0$ (where $m_0$ is the free-electron mass), we obtain $m_{\mathrm{II}}=1.50\mathrm{}{m}_0$, $m_{\perp }=0.21\mathrm{}{m}_0$, and a density-of-states mass ${m_D}^{*}=1.34\mathrm{}{m}_0$.