Water-Vapor-Inducedn-Type Surface Conductivity onp-Type Germanium

Abstract

By utilizing a direct reading instrument it is possible to measure the $n$-type surface conductance of the $p$-type germanium in an $n-p-n$ junction transistor as a function of relative humidity, ambient gas, and surface treatment. The results of these measurements indicate that the leakage conductance from the emitter to the collector may be predicted on the basis of a constant electron density at the surface which is independent of the applied bias but a critical function of the oxidation of the surface and the adsorbed gas. This conductance exhibits a transient character upon change in applied bias which may be correlated with similar transients in the conductance of a thin germanium crystal upon application of an external applied field. This comparison establishes that the inversion layer is caused by ionization of surface impurities rather than migration of ions along the surface. From the results of the experiments it is postulated that the density and type of carrier at the surface of an etched germanium crystal are a function of the surface treatment and gaseous ambient rather than the acceptor and donor density of the bulk germanium.