Experimental location of the surface and bulk 1/f noise currents in low noise, high gain NPN planar transistors

In light of recent apparent anomalies in medium frequency noise in planar transistors, a close examination has been made of the low frequency noise in gated low-noise NPN devices. It has been found that the 1/f noise can be attributed to surface and bulk noise components associated with the emitter-base junctions. These components have been separated and it is shown that the surface component can be dominant even in low-noise samples. It is also shown that the lumped resistance presented to the bulk noise current by the base region can be less than or greater than the base spreading resistance. It is suggested that this phenomenon is due to the distributed nature of the bulk noise current.