The photocurrent multiplication has been observed in a-Si : H pin photodiode films. We have experimented to temperature dependence of the photocurrent and the dark current in this photodiode by changing temperatures from 133K to 323K. We have found two dominant dark current components. The one is the thermal generation at crystal silicon/a-Si interface and the other is tunneling in i-a-Si : H. It has been found that the photocurrent avalanche multiplication in strongly affected with the geminate-recombination phenomena.
We propose an a-Se avalanche-type image pickup tube with a hole blocking stracture using carrier trap layer. A highly LiF doped a-Se film is used as the hole trap layer which makes the dark current less than 1 nA. The lowered dark current enables much Te doping into a-Se and consequently signal current for the red incident light reaches twice as much as that of conventional one.
In order to create an ultrahigh sensitivity camera for Hi-Vision, a prototype of a new image pickup tube combining a 25μm thick New Super-HARP (High-gain Avalanche Rushing amorphous Photoconductor) target with linch MM (Magnetic focusing and Magnetic deflecting)-type high definition electron optics was manufactured. The results of evaluation showed that the tube had ultrahigh sensitivity, high resolution and good lag characteristics. By applying this tube to the detecting system for a new method of micro angiography jointly developed with Tokai University and the National Laboratory for High Energy Physics, some interesting observations have been obtained and the possibility of clinical use was proved.