Abstract
Hall effect and resistivity measurements have been made in the temperature range 4.2–360 °K on several samples of n-type GaAs grown under oxygen atmosphere and without any other intentional dopings. The principal shallow donor in this material is considered to be Si. All samples exhibited impurity-band conduction at low temperature. Electron concentrations in the conduction band were calculated, using a two-band model, and then fitted to the usual equation expressing charge neutrality. A value of 2.3 × 10−3 eV was obtained for the ionization energy of the donors, for donor concentration ranging from 5 × 1015 cm−3 to 2 × 1016 cm−3. The conduction in the impurity band was of the hopping type for these concentrations. A value of 3.5 × 1016 cm−3 was obtained for the critical transition concentration of the impurity-band conduction to the metallic type.
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