Ultrafast carrier dynamics of surfactant-mediated-grown InAs/GaAs quantum-dot structures designed for THz applications

Quantum-dot (QD) materials have shown great promise for THz photoconductive devices. The generation of THz radiation relies on the excitation of highly-mobile carriers with sub-picosecond lifetimes. The band structure of QD materials grown for such THz applications leads to a multitude of energy bands/levels [1], onto which carriers can be excited. Here we show for the first time that the lifetime of carriers excited into the GaAs barriers (λ=800 nm) is up to two orders of magnitude shorter than when these are excited resonantly within the QDs (λ=1245 nm). We also present annealed QD-structures which exhibit faster carrier lifetimes than as-grown ones for most pump conditions, a feature unreported so far. Furthermore, an increase of carrier lifetime with the incident pump power is also unveiled for both annealed and as-grown samples. This study has significant implications in the understanding and optimal use of QD materials for THz generation applications [2].