Variable-range-hopping conductivity in compensatedn-type GaAs

Abstract

The low-$T$ conductivity of lightly doped, compensated, crystalline $n$-type GaAs epilayers is described by $\sigma ={\sigma }_0\exp [-{\left(\frac{T_0}{T}\right)}^s]+{\sigma }_c\exp \left[\frac{-(E_c-E_F)}{k_{B}T}\right]$. $s$ is found to vary from 0.2 to 0.27, implying that the Coulomb gap in the density of impurity states plays at best a minor role in the hopping conductivity ($T>\mathrm{}1\mathrm{}$ K) for $N_D\sim 5\times {10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and for compensations from 30% to 60%.