A Highly Sensitive Pickup Tube Using Avalanche Multiplication in an Amorphous Selenium Photoconductive Target and its Applications

In 1985, the author found for the first time that an experimental pickup tube (camera tube) with an amorphous selenium (a-Se) photoconductive target exhibits high sensitivity with quantum efficiency in greatly excess of unity under an applied target electric field greater than 9x10(7) V/m. This phenomenon results from a continuous and stable avalanche multiplication in the photoconductive target. We named the pickup tube with an amorphous photoconductive target operating in the avalanche-mode "HARP": High-gain Avalanche Rushing amorphous Photoconductor. A color camera equipped with the HARP tubes with a target film thickness of 25 mu m has a maximum sensitivity of 11 lx at F8. This means that the HARP camera is about 100 times as sensitive as that of CCD cameras for broadcasting. This ultra-high sensitivity HARP pickup tube was a powerful tool for reporting breaking news at night and other low-light conditions, the production of scientific programs, and numerous other application, including medical diagnoses, biotech research, and nighttime surveillance. It is expected that this high-sensitivity technology for image sensors will be useful for high-sensitivity 8K UHD cameras in the near future.