A novel quantum well infrared photodetector (QWIP) is proposed, which provides an unprecedented signal-to-noise ratio compared any other infrared detector. The key feature is the ability to inject light in the absorbing regions in the plane of the detector material layers, rather than surface normal to the detector material layers, as existing detectors do. This invention is expected to enable room-temperature detection of infrared light with high sensitivity and high speed, suitable for applications of infrared absorption spectroscopy, optical coherence tomography, light detection and ranging, and communications.
The QWIP was first demonstrated in 1987  and consistent research since then has improved the QWIP detection efficiency, but only for surface normal detection. Development of the QWIP was originally intended for infrared focal plane arrays suitable for infrared cameras. One challenge for these detectors is that absorption only occurs for light traveling in the plane of the material growth for detectors grown on <001> substrates.
This invention is of a detector that uses light incident on a single detector element in the plane of the material growth. It uses a similar absorbing region as typical QWIP (intersubband transition in a quantum well) and the waveguiding aspect has been developed for photodiodes using interband absorption. However, waveguiding QWIPs with high efficiency have not been possible due to poor index contrast on the native GaAs substrate. This new device, called a waveguide-QWIP, is possible because of the more advanced, yet commercially mature, fabrication technique of wafer bonding the photodetector material to a separate wafer, rather than fabricating the detector on the native substrate that the QWIP layers are grown. This importantly allows for a decrease in the number of quantum wells and a decrease in the cross-sectional area of current flow, while simultaneously maintaining the same optical absorption efficiency compared to the existing detector architectures. These features both increase the responsivity of the photodetector and decrease the dark current noise, thus significantly increasing the signal-to-noise ratio.
Competing technologies include surface normal QWIPs, quantum cascade detectors (QCDs), interband cascade detectors (ICDs), and mercury-cadmium-telluride detectors (MCTs). Another possible competing technology is deuterated L-alanine doped triglycine sulfate (DLaTGS) pyroelectric detectors, however, these detectors are only suitable for low-speed applications. The waveguide-QWIP performance is expected higher than these competing technologies in terms of detection speed, sensitivity, and noise levels. The cost to fabricate and produce the detectors is expected to be much lower.