A Vapor-Grown Variable Capacitance Diode

Germanium p-n junctions have been made which have a large fractional variation of capacitance with voltage and which have promise of being operable at high frequencies. These diodes are produced by a vapor-growth process in which the doping is switched from n-type to p-type during growth. Capacitances which vary as the reciprocal of voltage over a considerable range have been observed. This capacitance variation corresponds to a net donor concentration which decreases from its value at the junction approximately as the reciprocal of distance from the junction. At a position corresponding roughly to the edge of the transition region at breakdown, the net donor concentration abruptly increases. This rapid variation of capacitance with voltage and the low series resistance resulting from the discontinuity in doping level should result in high-frequency diodes, if the magnitude of the discontinuity can be increased sufficiently.