Frequency-dependent conductivity in lithium-diffused and annealed GaAs

We report on measurements of the frequency-dependent conductivity in lithium-diffused (Li-diffused) and annealed GaAs in the frequency range 10– 10 6 Hz and the temperature range 30– 300 K . Li diffusion into GaAs reduces the free carrier concentration and can make the material semi-insulating. Using admittance spectroscopy we show that the conduction in semi-insulating Li-diffused GaAs is due to hopping between localized centers. These centers are suggested to be associated with the gallium vacancy VGa and the gallium antisite GaAs. Furthermore, percolation is apparent in as-diffused samples, indicating that the material contains metallic precipitates. We suggest that the percolation is due to Li precipitation or formation of GaLi clusters during in-diffusion of lithium. At high frequency the AC conductivity is proportional to ωs. The value of s decreases with increasing temperature which suggests a correlated barrier hopping mechanism.