Compensator inhomogeneity in an extrinsic semiconductor

An inhomogeneous distribution of the principal dopant has a variety of well-known consequences for an extrinsic semiconductor. This paper considers an additional problem that can occur in a weakly compensated extrinsic semiconductor at low temperatures. The effective concentration of compensator centers then controls the behavior, in the dark or with weak illumination. Since that ’’effective compensator’’ density (for p-type material) is the algebraic difference between Nd compensating donors and Ns ionized acceptors shallower than the principal species, the low-temperature conduction can be greatly affected by local changes in the magnitude (and sign) of Nd−Ns. The distance range over which inhomogeneities such as undercompensated regions might exist even with minimum (Gaussian) variance is discussed. Compensator inhomogeneity effects are illustrated with data for weakly compensated mercury-doped germanium. Measurements of equilibrium transport coefficients, and of scanned photoconductive response, were indicative of a mixture of positively compensated and undercompensated regions.