Lateral Photocurrent Spectroscopy of Stacked InAs QDs Layers in Embedded Strain-Relaxed InGaAs Matrix

Lateral photocurrent spectroscopy was performed for stacked InAs QDs layers embedded in strain-relaxed In-GaAs matrix over the temperature range from 4 to 292 K. The InAs QDs sample was grown on GaAs substrate by MBE. Photocurrent was measured using a lock-in technique at 5 Hz, with the sample illuminated in normal-incidence geometry by monochromated white light from a halogen lamp. Photosensitivity was obtained from measured currents in dark and under illumination. Although peak positions from QDs and wetting layers were not clearly separated, the broad peak structure derived from the InAs QDs layers was continuously observed around 1400 nm. The obtained spectra correspond to the relative absorption spectra of the InAs QDs layers due to the relatively low electric field. The absorption tail in the sub-gap region ( $\lambda > 1400\ \text{nm}$ ) extended to longer wavelength side and increased as temperature increased. This indicates probably the presence of defect states activated thermally due to misfit dislocation in the strain-relaxed InGaAs layer near QDs.