Effect of well width on three-color quantum dots-in-a-well infrared detectors

Three-color InAs-InGaAs quantum dots-in-a-well (DWELL) detectors having different well sizes are presented. Three DWELL detectors (1388, 1373, and 1299) with different quantum well (QW) widths (120, 110, and 90/spl Aring/, respectively) have been characterized showing response peaks at three distinct wavelengths. The detector 1388 has peak wavelengths at /spl sim/6.25, /spl sim/10.5, and /spl sim/23.3 μm. The two peaks at 6.25 and 10.5 μm are believed to be due to bound-to-bound transitions from the ground state in the dot to a state in the well, whereas the longer wavelength peak (/spl sim/23.3 μm) which has a detectivity of 7.9×10/sup 10/ cm/spl middot//spl radic/Hz/W at 4.6 K under -2.2-V bias is due to an intersubband transition between the dot levels. The operating wavelength of these detectors in the short wavelength region can be tailored by changing the width of the QW. Spectral responsivity curves of 1373 and 1299 show a shift of the short wavelength peaks toward decreasing wavelength while the long wavelength peak remains around /spl sim/23.3 μm confirming that the particular transition is due to the quantum dot.