Anisotropic photoconductivity of InGaAs quantum dot chains measured by terahertz pulse spectroscopy

We report results of time-resolved terahertz (THz) pulse spectroscopy experiments on laterally ordered chains of self-assembled InGaAs quantum dots photoexcited with 400nm, 100fs laser pulses. A large anisotropy in the transient photoconductive response is observed depending on the polarization of the THz probe pulse with respect to the orientation of the dot chains. Fast (3.5–5ps) and efficient carrier capture into the dots and one-dimensional wetting layers underneath the dot chains is observed below 90K. At higher temperatures, thermionic emission into the two-dimensional wetting layers and barriers becomes significant and the anisotropy in the photoconductive signal is reduced.