Polarization dependence of absorption in strongly vertically coupled InAs/GaAs quantum dots for two-color far-infrared photodetector

Strongly vertically coupled InAs/GaAs quantum dots (QDs) with modulation doping are investigated, and polarization dependence of two-color absorptions was observed. Analysis of photoluminescence (PL) and absorption spectra shows that s-polarized absorptions at 10.0 and 13.4 μm stem from the first excited state E1 and the second excited state E2 in the QDs to the bound state EInGaAs in the InGaAs spacer, respectively, whereas p-polarized absorptions at 10.0 and 8.2 μm stem from the first excited state E1 and the ground Eg in the QDs to the bound state EInGaAs in the InGaAs spacer, respectively. These measurements illustrate that transitions from excited states are more sensitive to normal incidence, which are very important in designing QD infrared detector.