Diffraction-Grating-Free AlxIn1-xP/InAs Quantum Well Infrared Photodetector for Mid-Wavelength Infrared Imaging

Quantum well infrared photodetector (QWIP) technology still offers the best stability, uniformity, and reproducibility for thermal imaging applications. However, low quantum and conversion efficiencies of the standard QWIP have been bottlenecks for the wider utilization of these sensors. Another limitation of the QWIP technology is the need for a diffraction grating, establishing a barrier for pitch reduction. This article reports strain-compensated diffraction-grating-free Alx ${In}_{{1}-{x}}$ P/InAs QWIP focal plane array (FPA) operating in the mid-wavelength infrared (MWIR) band with characteristics much beyond the limits of standard QWIPs. Despite the absence of a diffraction grating, small-area ( $\sim 120~\mu $ m2) pixels with 4.8 and $5.2~\mu $ m peak and cut-off wavelengths exhibited peak absorption quantum efficiency (QE) of 33%, peak-specific detectivity of $\sim 2\times 10^{{11}}$ cm $\cdot $ ${Hz}^{\text {1/2}}$ /W, and background-limited performance with f/2 aperture at temperatures exceeding 100 K. The photoconductive gain is adjustable in a wide range under almost constant sensitivity, and the peak conversion efficiency exceeds 50% which is much higher than that of the conventional grating-coupled QWIP. The results of this work are important and promising for overcoming the bottlenecks of the QWIP technology and facilitating wider employment of this important sensor, including demanding imaging applications.