High-Frequency Properties of Epitaxial Silicon p-n Junctions at Low Temperatures

Abstract

Variable reactance epitaxial silicon p-n junctions with approximately constant impurity gradients were investigated at 5.85 Gc/sec, 1 Mc/sec and dc between room temperature and 2°K. The p-n junctions were B-P and B-As doped. The units with breakdown voltages larger than 11V (at 300°K) showed an exponential freeze-out of the carriers at 5.85 Gc/sec when the temperature was lowered. The units with less than 7.7 V breakdown voltage showed clearly impurity band conduction at low temperatures. The maximum change of the reactive component between large forward currents and the breakdown voltage was temperature independent within ±10% for all the wafers. The cutoff frequencies of the wafers at 300°K were between 190 and 320 Gc/sec. The units with large breakdown voltages (>14 V) had a negative differential resistance in the dc forward voltage-current characteristics at low temperatures. From an extrapolation of the present experiments one would expect, when the impurity gradient at the junction is increased to such a value that the breakdown voltage is about 5.5 V, that epitaxial silicon variable reactance p-n junctions will operate at microwave frequencies and liquid-helium temperatures with approximately the same losses as at room temperature.