Impurity band in lithium-diffused and annealed GaAs: Conductivity and Hall effect measurements

Originally n-type Si-doped GaAs turns p-type after Li indiffusion and consequent annealing at $200–600°\mathrm{C}.$ Temperature-dependent conductivity and Hall effect measurements carried out in the temperature range 30–300 K reveal conduction via impurity bands made up of shallow acceptors in addition to the valence-band conduction. Li diffusion into GaAs reduces the free-carrier concentration which leads to electrical resistivity as high as ${10}^7\Omega \mathrm{cm}.$ Annealing highly resistive samples at temperatures above $200°\mathrm{C}$ significantly decreases the room-temperature resistivity to 0.1–1 $\Omega \mathrm{cm},$ depending on the annealing temperature. For samples annealed at $300-400°\mathrm{C}$ we observe a metallic-type conduction which contributes to the conduction even at room temperature. In samples annealed at $500–600°\mathrm{C}$ the temperature dependence of the resistivity indicates that impurity conduction sets in at temperatures below 100 K. We discuss this conduction change in relation to enhanced gallium vacancy ${(V}_{\mathrm{Ga}})$ and gallium antisite $\left({\mathrm{Ga}}_{\mathrm{As}}\right)$ concentration in Li indiffused and annealed samples.