Electrical Conduction via Slow Surface States on Semiconductors

Steady-state and transient conductance of inversion layers created by acetone vapor on silicon $n-p-n$ bars were investigated. The interpretation gives strong evidence that the charge in the outer surface states can move in an electric field. The mobility of the charge is found to be of the order of ${10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$/volt sec for thick films. The mobility becomes progressively smaller in thinner films. It is found that inversion layers created by mobile charges may be unstable for certain applied voltages—in which case large potential jumps occur where the inversion layer meets the main $p-n$ junction. It is shown that in many cases the inversion layer current is multiplied while flowing through this potential jump. Possible multiplication mechanisms will be discussed.