Self-Limitation of Edge-Generated Currents in Single-Sided Microstrip Detectors after Type Inversion

The possibility that the performance of single-sided microstrip detectors may be compromised, after type inversion, by am untolerable increase in the leakage current due to contributions originating from the cut region represents one of the main reasons for the hesitation in adopting single-sided detectors for high-radiation environment applications. However, recent experimental results have shown that heavily irradiated, single-sided detectors exhibit no dramatic degradation due to edge-generated current, the latter never exceeding a small fraction of the overall detector leakage current. A qualitative interpretation for such results based on a one-dimensional model has been proposed by G. Lutz et al., suggesting that the edge-generated current is limited by the high resistivity of the undepleted bulk region. In this work, we present two-dimensional numerical simulations of the edge region of p+-n single-sided silicon microstrip detectors after type inversion. In particular, we show that, for high defect densities at the detector cutting edge, the local hole density approaches its equilibrium value. Correspondingly, the net generation rate saturates, this ultimately limiting the amount of current which can originate from the detector edge. Such a mechanism is suggested to be at the origin of the observed edge current limitation in type-inverted single-sided microstrip detectors. Quantitative comparisons with measurements from actual devices are currently being carried on, aimed at validating the proposed edge current limitation mechanism.