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°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 10⁷Ωcm. Annealing highly resistive samples at temperatures above 200°C significantly decreases the room-temperature resistivity to 0.1–1 Ωcm, depending on the annealing temperature. For samples annealed at 300–400°C we observe a metallic-type conduction which contributes to the conduction even at room temperature. In samples annealed at 500–600°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_Ga) and gallium antisite (Ga_As) concentration in Li indiffused and annealed samples.