Recent developments in quantum well infrared photodetectors

Rapid progress in quantum well infrared photodetectors (QWIPs) technology has made it possible to develop large format, high uniformity, and high performance QWIP focal plane arrays (FPAs) for a wide variety of infrared (IR) sensors and imaging applications. So far, all QWIP FPAs are made of n-type GaAs/AlGaAs material systems grown on GaAs substrates by the molecular beam epitaxy (MBE) technique due to the maturity of the III-V MBE growth and processing technologies However, due to quantum selection rules, normal incidence absorption is forbidden in n-type QWIPs As a result, n-type QWIPs are required to use dielectric or metal gratings to couple the IR radiation into the quantum wells under normal incidence illumination. On the contrary, normal incidence absorption is allowed for p-type QWIPs, and no grating couplers are needed for normal incidence absorption in p-type QWIPs. This property makes p-type QWIPs potentially more attractive for large format FPAs applications. In this paper we review recent developments in both n- and p-type QWIPs for mid-wavelength, long- wavelength and very long wavelength infrared (MWIR, L WIR, and VLWIR) detection. The basic device physics, structures, and performance parameters such as dark current, spectral responsivity, and detectivity for both n- and p-type QWIPs are depicted. A comparison of the advantages and drawbacks of n- and p-type QWIPs is given. Finally, multi-stack and voltage-tunable asymmetrical coupled quantum well QWIPs for multi-color detection in the MWIR and LWIR bands is also discussed.