Abstract
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. The sensitivity of conventional short-wave infrared cameras is limited by their readout noise level. 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. Recent theoretical predictions suggested that reducing the internal capacitance of detectors with internal gain can increase their sensitivity. Here, we show the experimental validation of this prediction for III-V heterojunction phototransistors. We have fabricated a 320 × 256 array of InGaAs/InP infrared phototransistors integrated with a conventional silicon readout circuit. 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. Characterization of a large number of pixels shows that 1 μm devices have significantly higher sensitivity than 2 μm devices. 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. 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 results suggest that the proposed phototransistors are promising for ultra-sensitive short-wavelength infrared cameras.
| Original language | English (US) |
|---|---|
| Article number | 191102 |
| Journal | Applied Physics Letters |
| Volume | 117 |
| Issue number | 19 |
| DOIs | |
| State | Published - Nov 9 2020 |
Funding
This work was supported by the W. M. Keck Foundation under a Research Grant in Science and Engineering and by partial funding from ARO Award No. W911NF-18-1-0429. This work was performed, in part, at the Center for Nanoscale Materials of Argonne National Laboratory. The use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This work utilized the Northwestern University Micro/Nano Fabrication Facility (NUFAB), which was partially supported by the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (No. NSF ECCS-1542205), the Materials Research Science and Engineering Center (No. NSF DMR-1720139), the State of Illinois, and Northwestern University. S.B. gratefully acknowledges support from the Ryan Fellowship and the International Institute for Nanotechnology at Northwestern University.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)