Dark-currents characterisation in charge-coupled devices

By operating a c.c.d. delay line in integration mode, that is stopping the transfer process for a relatively long integration time and then shifting the charge packets to the output, it is possible to make evident thermal generation processes known as `dark currents¿¿. The first part of the paper describes in detail the generation processes that take place in the structure during the integration time, in the case of uniform bulk and surface generation parameters. An experimental technique based on this mode of operation is then presented: it is shown that it allows the easy separation of bulk and surface components of the dark currents. This technique also allows the precise localisation of small electrically active defects, and some experimental results, supported by X-ray observations, are presented.