Intersubband optical absorption in quantum dots-in-a-well heterostructures

Abstract

The theoretical analysis of intersubband optical transitions for InAs∕InGaAs quantum dots-in-a-well (DWELL) detectors are performed in the framework of effective-mass envelope-function theory. In contrast to InAs∕GaAs quantum dot (QD) structures, the calculated band structure of DWELL quantitatively confirms that an additional InGaAs quantum well effectively lowers the ground state of InAs QDs relative to the conduction-band edge of GaAs and enhances the confinement of electrons. By changing the doping level, the dominant optical transition can occur either between the bound states in the dots or from the ground state in the dots to bound states in the well, which corresponds to the far-infrared and long-wave infrared (LWIR) peaks in the absorption spectra, respectively. Our calculated results also show that it is convenient to tailor the operating wavelength in the LWIR atmospheric window (8–12μm) by adjusting the thickness of the InGaAs layer while keeping the size of the quantum dots fixed. Theoretical predictions agree well with the available experimental data.