Reverse Epitaxial Silicon Diode for Hybrid Photomultiplier Tube

A new silicon multiplying structure, of the reverse epitaxial type, suitable for use in conjunction with a photocathode of a photomultiplier tube decreases the switching time for high current pulses. To obtain linear output current of 10 amps into a 50Ω load and switching times of the order of 10-9 sec, a passivated over-polarized diode of 30 μ thickness was employed. We studied the electrostatic focusing of the hybrid multiplier to decrease as much as possible the transit time (10-12 sec) of the 12 keV photoelectrons and transit time fluctuations. To protect the diode junction edge from cesium and antimony vapor, the diode is masked while these materials are deposited on the photo surface. The photocathode and the diode were then heated under the same high vacuum and the whole structure sealed by the transfer method. With a 300Ω cm silicon structure, linear currents to 4 amperes are obtained with a current risetime of 1.3 × 10-9 sec.