High responsivity, LWIR dots-in-a-well quantum dot infrared photodetectors

In this paper we report studies on normal incidence, InAs/In0.15Ga0.85As quantum dot infrared photodetectors (QDIPs) in the dots-in-a-well (DWELL) configuration. Three QDIP structures with similar dot and well dimensions were grown and devices were fabricated from each wafer. Of the three devices studied, the first served as the control, the second was grown with an additional 400 Angstrom AlGaAs blocking layer, and the third was grown on a GaAs n+ substrate with the intention of testing a single pass geometry. Spectral measurements on all three devices show one main peak in the long-wave IR (approximate to8 mum). The absorption was attributed to the bound-to-bound transition between the ground state of the InAs quantum dot and the ground state of the In0.15Ga0.85As well. Calibrated peak responsivity and peak detectivity measurements were performed on each device at 40, 60, and 80 K. For the same temperatures, frequency response measurements from similar to20 Hz to 4 kHz at a bias of V-b = -1 V were also performed. The addition of the blocking layer was shown to slightly enhance responsivity, which peaked at similar to2.4 A/W at 77 K, V-b = -1 V and responsivity was observed to be significantly reduced in the single pass (n+ substrate) sample. The rolloff of the frequency response was observed to be heavily dependent on temperature, bias, and irradiance. The results from the characterization of each sample are reported and discussed. (C) 2003 Elsevier B.V. All rights reserved.