Surface-Dependent Losses in Variable Reactance Diodes

Surface effects may seriously degrade the high frequency performance of a semiconductor junction diode used as a variable reactance element without significantly degrading the diode's dc characteristics. Measurements on both p+n and n+p germanium alloy junction diodes have yielded a diode series equivalent resistance component in excess of the calculated integrated bulk resistance. This excess resistance decreased with frequency approximately as 1/f and for freshly etched devices could be varied by changing the atmosphere surrounding the diode. Those ambients which yielded a maximum surface-determined junction breakdown voltage also yielded a maximum frequency-dependent excess resistance. A model which can explain these observations assumes a surface inversion layer contiguous with the alloy junction.