![]() 11 Unfortunately, readout integrated circuits (ROICs) add significant noise to each frame, especially at high frame rates.Ĭurrently, commercial SWIR imaging sensors are dominated by InGaAs PIN photodetectors due to their low leakage current and short response time. For example, ground-based adaptive optics for astronomical imaging requires kHz speed to measure real-time atmospheric interference as well as high sensitivity to detect leftover starlight leaking around an occluding coronagraph. In addition to the high sensitivity, there is a great demand for high-speed infrared cameras to achieve real-time imaging. While tremendous effort has been made to achieve single photon imaging using avalanche photodiodes (APDs), photomultiplier tubes, quantum-dot field-effect transistors (QD-FETs), and resonant tunneling diodes (RTDs), 2,6–10 there is still significant room for improvement. 1–5 Single-photon imaging at thermoelectrically accessible temperatures (i.e., above ∼200 K) is the ultimate goal. Ultra-sensitive and fast detection for short-wavelength infrared (SWIR) is an essential requirement in an increasing number of applications, including quantum information processing, Raman spectroscopy, quantum cryptography, astronomical imaging, biological imaging, light detection and ranging (LiDAR), and optical time domain reflectometers (OTDRs). These results suggest that the proposed phototransistors are promising for ultra-sensitive short-wavelength infrared cameras. Interestingly, the processing variation in the 1 μm devices resulted in variation in sensitivity, and a good number of devices show sensitivity to less than 10 photons. These have an average noise equivalent photon sensitivity of about 20 photons at a camera frame rate of ∼500 frames per second, which is better than the best existing infrared cameras with a similar cutoff wavelength and frame rate. Characterization of a large number of pixels shows that 1 μm devices have significantly higher sensitivity than 2 μm devices. The array is made of two groups of pixels: 50% are devices with a 1 μm base diameter and the other 50% with a 2 μm base diameter. We have fabricated a 320 × 256 array of InGaAs/InP infrared phototransistors integrated with a conventional silicon readout circuit. ![]() Here, we show the experimental validation of this prediction for III–V heterojunction phototransistors. Recent theoretical predictions suggested that reducing the internal capacitance of detectors with internal gain can increase their sensitivity. This limitation can be addressed by the internal gain of the sensors, but only if fast response time and low dark current are achieved simultaneously. The sensitivity of conventional short-wave infrared cameras is limited by their readout noise level. Ultra-sensitive and fast infrared imaging has become increasingly important in applications that require high frame rates at low light levels, such as exoplanet imaging.
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