CHARGE-TRANSPORT IN A-SI-H DETECTORS - COMPARISON OF ANALYTICAL AND MONTE-CARLO SIMULATIONS

To understand the signal formation in hydrogenated amorphous silicon ( a-Si:H) p-i-n detectors, dispersive charge transport due to multiple t rapping in a-Si:H tail states is studied both analytically and by Mont e Carlo simulations: An analytical solution is found for the free elec tron and hole distributions n(x, t) and the transient current I(t) due to an initial electron-hole pair generated at an arbitrary depth in t he detector for the case of exponential band tails and linear field pr ofiles; integrating over all e-h pairs produced along the particle's t rajectory yields the actual distributions and current; the induced cha rge Q(t) is obtained by numerically integrating the current. This gene ralizes previous models used to analyze time-of-flight experiments. Th e Monte Carlo simulation provides the same information but can be appl ied to arbitrary field profiles, field dependent mobilities and locali zed state distributions. A comparison of both calculations is made in a simple case to show that identical results are obtained over a large time domain. A comparison with measured signals confirms that the tot al induced charge depends on the applied bias voltage. The applicabili ty of the same approach to other semiconductors is discussed.