Studies of the Response Speed of Silicon Surface Barrier Detectors, When Irradiated with Different Particles

The rise time of produced surface barrier detectors fort¿-particles, fission fragments and conversion electrons was measured with and without over-voltage and compared with calculations. The detectors were produced from n-type silicon with resistivities in the range, 250¿cm to 9000 ¿cm. The best rise times, ¿(0-63%), obtained up to now, are ¿0.8 ns for alphas (241Am) and 1.4 ns for fission fragments (252Cf) at high fields (system rise time, ¿¿0.6 ns included). The contribution of the plasma time, ¿p, due to the erosion of the ionisation tracks with their high carrier density by the field was studied in some more detail. ¿p vs. Em (effective field), derived from the rise time measurements, seems to be a relatively pure exponential dependence, ¿p ¿ k Em-n, Por a given detector at fields greater than 500 V/cm (0.7 < n < 1.3). ´k´ is a constant, dependent on particle type. With fission fragments from 252Cf the time jitter of correlated fragments in selected energy ranges was measured by irradiating two detectors in a wide angle (sandwich counter). A minimum jitter (F.W.H.M.) of 90 ps was reached for threshold detection. Zero crossing circuitry was also used for time detection to have an idea of the probable pulse shape jitter from fragments irradiating a detector under different angles. (Different orientation of the particle track with respect to the field). Such jitter seems to exist, also at relatively high fields.