Intraband absorption in n-doped InAs/GaAs quantum dots

We have investigated the intraband absorption within the conduction band of InAs/GaAs quantum dots. The islands obtained by self-organized epitaxy are modulation doped with a silicon planar doping 2 nm below the dot layer plane. The dots exhibit infrared absorption polarized along the growth axis in the midinfrared spectral range. The absorption is maximum around 150 meV with a large broadening around 130 meV. This broadening is attributed to size fluctuations within the one dot layer plane and the consequent variation of the electron confinement energy with the dot size. The magnitude of the absorption along the growth axis for the one dot layer plane is ≈2.5×10−2% which corresponds to an equivalent absorption cross section σz≈3.1×10−15 cm2. We show that the intraband absorption can also be clearly observed using a photoinduced infrared absorption technique with the doped quantum dots.