A high frequency silicon avalanche photodiode

An NPπP silicon avalanche photodiode with an NπP guardring is described. The diode was designed for high-frequency operation in the visible and near infrared spectrum and was fabricated on epitaxial material using standard silicon planar techniques. The active avalanche region is 10 mils in diameter and the depletion layer width determined by the epitaxial layer is 4.7 microns. The diode is mounted in a microwave pill package, that allows for easy application in coaxial connectors or printed circuit boards. Measurements of the low frequency noise characteristics show them to be in agreement with the theory of McIntyre. For avalanche gain, M, less than 100 the noise power increases with M to the 2.4 power. For larger gains there is a more rapid increase in the noise. Noise measurements at one GHz show the same slope of 2.4 on the noise power versus dc gain curve at M up to 100. At gains above this the diode gain-bandwidth product (100 GHz) limits the noise power to a slope of 1. Gains up to 200 were observed at low frequencies without the presence of excessive noise due to microplasmas. Calculations show the diode in a typical system would have an N.E.P. of 10^-12WHZ-1/2, for a one GHz bandwittt and an avalanche gain of 30.