Diffraction-Grating-Free Al_xIn_1-xP/InAs Quantum Well Infrared Photodetector for Mid-Wavelength Infrared Imaging

Quantum well infrared photodetector technology still offers the best stability, uniformity and reproducibility for thermal imaging applications. However, low quantum and conversion efficiencies of the standard quantum well infrared photodetector have been bottlenecks for wider utilization of these sensors. Another limitation of the quantum well infrared photodetector technology is the need for diffraction-grating establishing a barrier for pitch reduction. This paper reports strain-compensated diffraction-grating-free Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub>In<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub>P/InAs quantum well infrared photodetector focal plane array operating in the mid-wavelength infrared band with characteristics much beyond the limits of standard quantum well infrared photodetectors. In spite of the absence of diffraction-grating, small-area (~120 μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) pixels with 4.8 and 5.2 μm peak and cut-off wavelengths exhibited peak absorption quantum efficiency of 33%, peak specific detectivity of ~2×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cmHz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup>/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 quantum well infrared photodetector. The results of this work are important and promising for overcoming the bottlenecks of the quantum well infrared photodetector technology and facilitating wider employment of this important sensor including demanding imaging applications.