Investigation of carrier capture dynamics in InAs/GaAs single-layer quantum dots using terahertz time-resolved spectroscopy

Abstract

We observe carrier capture saturation at high excitation fluence in InAs/GaAs single-layer quantum dots using an optical pump-terahertz probe experiment conducted at room-temperature. Results show that carrier lifetime using a 0.4 mW optical pump was relatively constant at 500 ps, whereas the sample exited by 7.0 mW optical pump has lifetime of 3.7 ns immediately upon photoexcitation. Carrier lifetimes for all optical pump powers considered were observed to decrease and converge to around 500 ps after sufficient time. Calculations show that the 0.4 mW pump has photon density of 9.60 × 1010 photons/cm2 with a corresponding carrier density of 3 to 4 photoexcited carriers per dot. Meanwhile, the 7.0 mW pump has photon density of 1.68×10¹² photons/cm² with carrier density of 64 to 65 carriers per dot. This could imply that any increase in the excitation fluence may result to the filling of QD states, leading to an increase in the carrier lifetime of the sample.