Internal Pulse Amplification in High Field, Silicon Radiation Detection Junctions

Significant internal pulse amplification has been observed in silicon p-n junction radiation detectors operated in the very high field (but prebreakdown) region. Such internal electric field values (peak fields of 60 - 250 kilovolts cm-1) are attainable over distances of up to 250 microns through the use of geometrical control of the field existing at the surface of the junction. Amplification factor for the simple P + N geometry studied thus far is not constant being greatest for the short range particles and decreasing as particle range into the detector increases. In the amplifying mode, a directional effect is observed with amplification being dependent upon energy loss in the region of highest field (and thus the direction of the particle). Detector response has been measured for incident alpha particles, beta particles in the energy range from 0.04 MeV to minimum ionizing, protons from 0.5 - 3.0 MeV, and for 5 keV x-rays. Pulse risetimes which should be in the sub-nanosecond range for these geometries have been measured with alpha particles and with synchronous 0.88 and 1.06 micron wavelength photons from pulsed lasers with the detector being able to follow laser pulses with 2 - 5 nanosecond risetime. It is believed that the magnitude of internal amplification makes feasible the use of tunnel diodes in associated circuitry for numerous applications. Preliminary results to this end are briefly discussed.