Subpicosecond carrier dynamics in low-temperature grown GaAs as measured by time-resolved terahertz spectroscopy

The transient photoconductivity in a 1 μm layer of low temperature grown GaAs (LT-GaAs) on a GaAs substrate was measured using time-resolved terahertz spectroscopy. When photoexcitation occurs at 400 nm we find a time-dependent mobility that increases from $\text{400±100}$ to $\text{1100±100\hspace{0.5em}}{\mathrm{cm}}^2\hspace{0.17em}{\mathrm{V}}^{\text{−1}}\hspace{0.17em}{\mathrm{s}}^{\text{−1}}$ with a time constant of 2 ps. Photoexcitation at 800 nm produces a time-independent mobility of $\text{3000±500\hspace{0.5em}}{\mathrm{cm}}^2\hspace{0.17em}{\mathrm{V}}^{\text{−1}}\hspace{0.17em}{\mathrm{s}}^{\text{−1}}.$ We determine the carrier lifetime in LT-GaAs to be 1.1 ± 0.1 ps.