Oxide embedding structures and nanoscale multiplication regions would afford improvements in performance.
Nano- multiplication- region avalanche photodiodes (NAPDs), and imaging arrays of NAPDs integrated with complementary metal oxide/semiconductor (CMOS) active-pixel-sensor integrated circuitry, are being developed for applications in which there are requirements for high-sensitivity (including photoncounting) detection and imaging at wavelengths from about 250 to 950 nm. With respect to sensitivity and to such other characteristics as speed, geometric array format, radiation hardness, power demand of associated circuitry, size, weight, and robustness, NAPDs and arrays thereof are expected to be superior to prior photodetectors and arrays including CMOS active-pixel sensors (APSs), charge-coupled devices (CCDs), traditional APDs, and microchannelplate/ CCD combinations.
The advantages of the NAPD concept over prior photodetector and array concepts are attributable to the oxide embedding SOI structure and the nanoscale multiplication region. The electrically insulating property of the oxide embedding structure would prevent cross-talk among pixels. The nanoscale design of the multiplication region could be tailored to obtain unique avalanche properties. In contrast, (1) the pixels of a traditional APD array are all built on one common substrate, leading to severe cross-talk and (2) a traditional APD contains a relatively large multiplication region, within which electron avalanches are localized to a few small volumes. Efforts have been made to obtain uniformity in the multiplication regions of traditional APDs, but inasmuch as electron avalanches are very sensitive to the local electric-field fluctuations, it is difficult to obtain uniformity in large arrays of conventional APDs.
This work was done by Xinyu Zheng, Bedabrata Pain, and Thomas Cunningham of Caltech for NASA’s Jet Propulsion Laboratory.
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