Lithium-diffused and annealed GaAs: An admittance spectroscopy study

We study lithium-diffused and annealed GaAs by admittance spectroscopy in the frequency range $10–{10}^6\mathrm{Hz}$ and the temperature range 30–300 K. Li diffusion turns the GaAs semi-insulating but subsequent out-diffusion of Li increases the conductivity and makes the samples p type. It is demonstrated that the conduction in semi-insulating Li-diffused GaAs is due to thermally activated carriers in the valence-band percolating around insulating metallic precipitates. At high frequencies the ac conductivity is proportional to ${\omega }^x,$ with x being close to unity value, independent of temperature. We suggest that the percolation may be due to metallic precipitates formed during in-diffusion of lithium and following cooling. After subsequent annealing the ac conductivity becomes proportional to ${\omega }^s$ at high frequencies with the value of s decreasing with increasing temperature. The temperature dependency of s suggests a correlated barrier hopping mechanism in a band of defects. We attribute these defects to gallium vacancies $V_{\mathrm{Ga}}$ and gallium antisites ${\mathrm{Ga}}_{\mathrm{As}}.$