Low strain Quantum Dots in a Double Well Infrared Detectors R. V. Shenoi a , J. Hou a,b , Y. Sharma a , J. Shao a , T. E Vandervelde a , and S. Krishna a a Center for High Technology Materials, ECE Department, University of New Mexico, 1313 Goddard St. SE, Albuquerque, New Mexico 87106; b Biology Department, Zanvyl Krieger School of Arts and Sciences, The Johns Hopkins University, Baltimore, MD 21218. ABSTRACT We report the fabrication of low strain quantum-dots-in-a-double-well (DDWELL) infrared photodetector where the net strain on the system has been reduced by limiting the total indium content in the system. The detector consists of InAs dots embedded in In 0.15 Ga 0.85 As and GaAs wells with a Al 0.1 Ga 0.9 As barrier, as opposed to In 0.15 Ga 0.85 As wells and a GaAs barrier in standard dots-in-a-well (DWELL) detector. The structure was a result of multilevel optimization involving the dot, well layers above and below the dot for achieving the desired wavelength response and higher absorption, and the thickness of the barriers for reduction in dark current. Detector structures grown using solid source molecular beam epitaxy (MBE) were processed and characterized. The reduction in total strain has enabled the growth of higher number of active region layers resulting in enhanced absorption of light. The detector shows dual color response with peaks in the mid-wave infrared (MWIR) and the long-wave infrared (LWIR) region. A peak detectivity of 6.7×10 10 cm. √ Hz/W was observed at 8.7μm. The detector shows promise in raising the operating temperature of DWELL detectors, thereby enabling cheaper operation. Keywords: Quantum Dots, Infrared detector, Dots-in-a-Well Detector, 1. INTRODUCTION Infrared sensors in the 3-25 μm region are highly sought after for applications in missile defense, night vision and fire fighting equipment. 1–4 Efforts are on to develop third generation detectors having the ability to detect multiple colors and having better yield. Quantum dot infrared photodetectors (QDIP) and quantum dots-in-a-well (DWELL) detectors have been identified as a promising alternative due to their low dark current and ability to absorb normal incident radiation. 1, 2, 5, 6 These detectors use growth technologies for III-V materials and hence it is possible to produce good spatial uniformity over a large area. This is essential for fabrication of large area focal plane arrays (FPA). The current state of the art detectors in this wavelength regime, based on mercury cadmium telluride (MCT) suffer from the spatial nonuniformities in growth which in turn creates a considerable shift in the bandgap and the absorption wavelength. The DWELL detector is a combination of the QDIP and the Quantum Well Infrared Photodetector (QWIP), where the quantum dots are placed inside a quantum well. It makes use of intersubband transitions from the dot to the well and from the dot to the quasi-bound state for detection. 7–9 Moreover, the quantum confined Stark effect (QCSE) associated with asymmetrically designed DWELLs result in a bias dependent spectral response making it suitable for multi-spectral detection. 10 Recently a 640×512 FPA has been demonstrated using the InAs/InGaAs DWELL detector and a two color FPA has also been demonstrated using the transition in DWELL detector. 7, 11–16 Traditional DWELL detectors use multiple stacks of InAs/In 0.15 Ga 0.85 As/GaAs where the InAs quantum dots (QDs) are embedded in a In 0.15 Ga 0.85 As well with GaAs barriers in a GaAs substrate. The transitions in the detection process are the ones from the dot to the well and the dot to the quasi-bound state giving rise to two color response in the mid- wave infrared (MWIR, 3-5 μm) and the long-wave infrared (LWIR, 8-12 μm) regime. 1 The number of stacks in the active region are limited by the strain introduced in the system by growing the InAs QD and the In 0.15 Ga 0.85 As well on a GaAs substrate. This results in a low absorption cross-section and leads to low quantum efficiency (QE) of these detectors. 17 However the growth of QDs is a self-assembled process that results from the lattice mismatch between the QD material and the substrate. Hence strain cannot be totally avoided in these systems. Several ways have been suggested to improve Corresponding author: R. V. Shenoi E-mail: rshenoi@ece.unm.edu Infrared Spaceborne Remote Sensing and Instrumentation XVI, edited by Marija Strojnik, Proc. of SPIE Vol. 7082, 708207, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.795661 Proc. of SPIE Vol. 7082 708207-1