Researchers at Northwestern University, Evanston, Ill., have developed a new approach to quantum device design that has produced the first gain-based long-wavelength infrared (LWIR) photodetector using band structure engineering based on a type-II superlattice material.<\/p>\n
This new design, which demonstrated enhanced LWIR photodetection during testing, could lead to new levels of sensitivity for next-generation LWIR photodetectors and focal plane array imagers. The work could have applications in earth science and astronomy, remote sensing, night vision, optical communication, and thermal and medical imaging.<\/p>\n
\u201cOur design can help meet the urgent demand for ultra-sensitive photodetectors,\u201d said Manijeh Razeghi, Walter P. Murphy professor of electrical and computer engineering, who led the study. \u201cThe architecture uses a unique type-II superlattice material that optimizes LWIR photodetectors to run with low power, higher optical gain, and excellent stability.\u201d<\/p>\n
While recent advances in semiconductor materials and devices have led to notable progress in the development of photodetectors that can capture LWIR wavelengths, state-of-the-art LWIR detection technology still suffers from shortcomings. Many photodetectors rely on mercury cadium telluride as a semiconductor, a material that can achieve excellent sensitivity and speed, but also produces low photocurrent gain and excess spectral noise.<\/p>\n
Razeghi designed the photodetector using a type-II superlattice, a material system known for its outstanding growth uniformity and exceptional band structure engineering \u2014 the ability to control the band gap in a material, the space where no electron charge is present. This made it an optimal alternative semiconductor to mercury cadmium telluride for a LWIR system. Her team applied the new material to a heterojunction phototransistor device structure, a detection system known for its high stability, previously limited to short-wave and near infrared detection.<\/p>\n
During testing, the type-II superlattice allowed each part of the photodetector to be carefully tuned to use the phototransistor to achieve high optical gain, low noise, and high detectivity.<\/p>\n
\u201cThe material\u2019s demonstrated flexibility allows for meticulous quantum mechanics-based band structure engineering for the heterostructure design, making it a versatile candidate to push the limits of infrared detection,\u201d Razeghi said.<\/p>\n
This novel artificial quantum structure opens the door toward next-generation high-gain photodetectors with potential for high-speed applications with ultra-sensitive detection capabilities for single photon detection.<\/p>\n
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