Longwave infrared (LWIR) sensing and imaging has become a crucial technology for uses as varied as surveillance, autonomous vehicle navigation, and disease detection. New approaches to LWIR sensing are always welcome, at least if they have advantages. Researchers at Fudan University and the Chinese Academy of Sciences (both in Shanghai, China) have provided such advantages by taking the technology of charge-sensitive infrared phototransistors (CSIPs), which are composed of gallium arsenide/aluminum gallium arsenide (GaAs/AlGaAs) double quantum wells and which had previously been demonstrated to have much higher LWIR photoresponsivity than conventional approaches, and taking the first stab at making an imaging array of such devices.
The first experimental prototype is a 1 × 8 linear array of CSIPs; the device has a photoresponsivity of more than 50 A/W at its peak wavelength of 11 μm, which the researchers say is two orders of magnitude higher than for conventional LWIR detectors. While the CSIPs themselves are cryogenically cooled, the readout circuits are not, making for a simpler device. Standard planar photolithography was used to fabricate the CSIPs. The researchers built their own eight-channel pulse generator with identical pulse parameters for each channel and tunable delays between neighboring channels. In the future, a higher sensor count and 2D formats could make this approach useful for low-photon-flux LWIR imaging applications. Reference: H. Wang et al., Appl. Phys. Lett. (2020); https://doi.org/10.1063/5.0007724.