Long-Wavelength Quantum Well Infrared Photodetectors

A majority of IR sensors used for imaging arrays operating in the long-wavelength IR region between 8 µm-12 µm are based on mercury cadmium telluride (HgCdTe). This material system is unable to satisfy all the requirements imposed by modem applications. Structural difficulties due to poor uniformity, high defect densities, and weak bond strengths cause difficulties in manufacturing large IR focal plane array cameras. As an alternative, quantum well infrared photodetectors (QWIPs) utilising intersubband absorption between gallium arsenide (GaAs) wells and aluminium gallium arsenide (AIGaAs) barriers were perfected. These QWIPs possess better uniformity in comparison to HgCdTe detectors, and QWIP imaging arrays have recently become commercially available. However, the responsivity of GaAs/AlGaAs QWIPs is still lower than HgCdTe detectors. To further improve the responsivity of QWIP detectors, QWIPs with wells or barriers of GaInAsP instead of AlGaAs have been developed. Results of QWIPs made from the material systems GaAs/GaInP, GaInAs(P)/InP, (Al)GaInAs/InP, and GaInAs/AllnAs have been discussed