RESPONSE OF SEMICONDUCTOR SURFACE-BARRIER COUNTERS TO NITROGEN IONS AND ALPHA PARTICLES

Abstract

Silicon and germanium surface-barrier counters for detection of short- range ionizing particles were constructed and tested. Measurements with artificial pulses showed that the barrier height V/sub 0/ is about 0.6 volt in silicon and that with variation of the applied bias V. the barrier capaciiy is linear with (V/sub 0/ + V)/sup -1/2/ as is expected from the Schottky exhaustion- layer theory. Measurements with natural alpha particles showed that the charge-collection efficiency is probably 100%, the energy loss per electronhole pair is 3.50 hr at 1500 deg 0.05 ev in silicon and 2.83 hr at 1500 deg 0.03 ev in germanium, and the pulse-height resolution is outstandingly good. Two independent measurements with cyclotronproduced N/sup 14/ ions up to 25 Mev showed that the pulse-height response is linear with energy. The ratio of N/sup 14/ to alpha pulse height is equal to the energy ratio to within 1%. The response to a continuous energy distribution of alpha particles indicates that the sensitive depth is on the order of 20 mu greater than the barrier depth calculated from the Schottky theory. The excess sensitive depth probably represents diffusion into the exhaustion layer of holes produced below it. (auth)