Investigation of carrier mobility in InAs/GaAs self-assembled quantum dots via optical pump-terahertz probe spectroscopy

Abstract

We investigate the photocarrier mobility in an indium arsenide on gallium arsenide (InAs/GaAs) self-assembled quantum dot sample by extracting the Drude scattering time through optical pump-terahertz probe spectroscopy. An 800 nm optical pump beam was used to generate photocarriers in the sample at 5.71 and 100.00 μJ cm⁻² optical fluence. Carrier mobility was then probed by transmitting a terahertz (THz) pulse after photoexcitation which was sampled in the time domain. The real and imaginary parts of the sample's complex conductivity were calculated from the corresponding frequency spectra of the transmitted THz pulse. Drude global fitting was performed simultaneously for both real and imaginary parts of the conductivity. Both plasma frequency and scattering time were obtained as fitting parameters. Results reveal a possible transition from the GaAs barrier region to the InAs wetting layer (WL) region as the dominant recombination site for carriers. Ultrafast relaxation and trapping will cause carriers to occupy the lowest available energy state. This suggests a possible state-filling phenomenon for carriers in the InAs WL region at high optical fluence.