This paper discusses recent and future advancements in the field of quantum dots-in-a-well (DWELL) focal plane arrays (FPAs). Additionally, for clarity sake, the fundamentals of FPA figures of merit are reviewed. The DWELL detector represents a hybrid between a conventional quantum well photodetector (QWIP) and a quantum dot (QD) photodetector (QDIP). This hybridization, where the active region consists of QDs embedded in a quantum well (QW), grants DWELLs many of the advantages of its components. This includes normally incident photon sensitivity without gratings or optocoupers, like QDIPs, and reproducible control over operating wavelength through 'dial-in recipes' as seen in QWIPs. Conclusions, drawn by the long carrier lifetimes observed in DWELL heterostructures using femtosecond spectroscopy, have recently backed up by reports of high temperature operation results for DWELL FPAs. This paper will conclude with a preview of some upcoming advances in the field of DWELL focal plane arrays.
In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot
infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots
embedded in InGaAs quantum wells. By adjusting the InGaAs well thickness, our structure allows for the manipulation
of the operating wavelength and the nature of the transitions (bound-to-bound, bound-to-quasibound and bound-to-continuum)
of the detector. Based on these principles, DWELL samples were grown using molecular beam epitaxy and
fabricated into 320 x 256 focal plane arrays (FPAs) with Indium bumps using standard lithography at the University of
New Mexico. The FPA evaluated was hybridized to an Indigo 9705 readout integrated circuit (ROIC) in collaboration
with QmagiQ LLC and tested with a CamIRaTM system manufactured by SE-IR Corp. From this evaluation, we report
the first two-color, co-located quantum dot based imaging system that can be used to take multicolor images using a
single FPA. We demonstrated that we can operate the device at an intermediate bias (Vb=-1.25 V) and obtain two color
response from the FPA at 77K. Using filter lenses, both MWIR and LWIR responses were obtained from the array at the
same bias voltage. The MWIR and LWIR responses are thought to be from bound states in the dot to higher and lower
lying states in the quantum well respectively. Temporal NEDT for the DWELL FPA was measured to be 80mK at 77K.
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