Diffusion dark current in CCDs and CMOS image sensors

Long neglected as unimportant, the dark current that arises due to diffusion from the bulk is assuming a more important role now that CCD and CMOS imagers are finding their way into consumer electronics which must be capable of operating at elevated temperatures. Historically this component has been estimated from the diffusion related current of a diode with an infinite substrate. This paper explores the effect of a substrate of finite extent beneath the collecting volume of the pixel for both a front-illuminated device and a thinned back-illuminated device and develops corrected expressions for the diffusion related dark current. The models show that the diffusion dark current can be much less than that predicted by the standard model.