Gold-Epitaxial Silicon High-Frequency Diodes

A diode based on the properties of an evaporated gold contact on n-type epitaxial silicon has speed comparable to point contact diodes. The space charge region at zero bias can be designed to penetrate up to the impurity tail at the interface, thus reducing series resistance. An encapsulated diode was made with a 1-mil diameter gold contact on an epitaxial layer 1.5 microns thick having a surface doping of 1 × 1015donors per cm3. The zero-bias RC product of this diode is less than 1 × 10−12second. Under forward bias the electron transit time through the epitaxial layer is less than 2 × 10−11second. The breakdown voltage of experimental diodes is greater than 10 volts. Stress aging experiments in an inert atmosphere show no deterioration of electrical properties at temperatures up to the gold-silicon eutectic (370°C). This diode was used as a harmonic generator at 11 gc with an efficiency comparable to that of a gallium arsenide point contact diode.