Solid-State Charpak Detector with Unipolar and Ultrafast Time-Differential Pulse Response

For the first time we have fabricated a high granularity micropattern solid-state detector (MSSD) with the unipolar time-differential property for ultrafast pulse response. Optical, x-ray, and gamma-ray photoconductivity measurements prove the unipolar time-differential response with a speed improvement factor of ~400 for amorphous selenium MSSD. The significance of the results presented here is the ability to reach the intrinsic physical limit for detector pulse speed by transitioning from the transit-time-limited response, which depends on the bulk carrier transport mechanism, to range-limited response set by the spatial dispersion of the photo-induced carrier cloud. Furthermore, the combination of the time-differential and the avalanche-multiplication properties of the proposed micropattern solid-state detector can yield another great leap forward in the field of radiation detectors with applications ranging from high-energy, nuclear, and astro- physics, to industrial and medical diagnostics, and crystallography.