Modal analysis of SPRITE transport processes

Carrier transport in signal processing in the element (SPRITE) detectors is an important phenomenon because it determines properties such as the responsivity and the modulation transfer function (MTF). The previous literature has presented approximate solutions to the transport problem that neglect boundary effects, which have long been thought to play a major role in SPRITE behavior. In this paper we present a new solution to the problem through the use of modal analysis. This method intrinsically includes the three dimensional boundary conditions, and thus is more complete than the previous analysis. Through the analysis, certain dimensionless numbers arise which can be used to characterize SPRITE structure parameters and clarify how these parameters impact device performance. Further, we use this solution to derive an expression for the MTF. The effects of the boundary conditions and the device geometry on MTF are investigated using the new theory. Our results show that the quality of the passivated surfaces has a weak influence on the MTF; however, the device width affects the MTF performance more strongly when the passivation is poor. The effect of blocking at the contacts is investigated. It is found that while marginal improvements in MTF roll-off could be achieved by making the contacts highly ohmic, the maximum signal amplitude is obtained with partially blocking contacts.