Observation of intracell avalanche amplification in charge-coupled devices (abstract)

Abstract

At present, in various imager devices, the phenomenon of avalanche amplification—in uniform MIS (metal-insulator-semiconductor) structures is extensively used. For these structures, the current is, as a rule, the output signal. The authors of this paper have previously made the supposition that an alternative approach can be feasible—to achieve the regime of avalanche amplification in MIS imagers dealing with electric charges, and in particular, to obtain intracell amplification in commercial charge-coupled devices (CCD) when detecting x-ray images. In this paper experiments in which the intracell avalanche amplification is obtained in a 1000-element commercial linear CCD imager are described. During direct detection of x rays and red optical radiation, no avalanche amplification takes place because of the peculiarities of the structure of the active regions of this device. However, in the blue spectral range there has been revealed, at room temperature, a stable uniform amplification of the order of 10, limited mainly by the multiplication of thermogenerated charges and, possibly, by a tunneling breakdown. At the temperature of liquid nitrogen, inner amplification factor roughly equal to 105–106 has been obtained in the active regions of the device and, hence, the observation of the signals from individual photogenerated carriers has become possible. The corresponding total amplification factor (of the order of 104) allows one to detect light fluxes in the blue spectral range, which are totally disguised by noise if the amplification is absent. Such a high amplification factor in the optical region has made it possible to demonstrate the effectiveness of the avalanche regime at the temperature of liquid nitrogen when detecting x radiation, using its conversion to light on the luminophor. The amplification factor achieved is about 102. In conclusion, some peculiarities of the avalanche break-down of nonuniform MIS structures and, in particular, of in the active regions of the CCD under consideration have been analyzed. The structures, oriented to an effective avalanche amplification when detecting x-ray and optical radiation are discussed as well.