Properties of Grain Boundaries in Gold-Doped Germanium

It has been found that grain boundaries produce a path of relatively low electrical resistance at temperatures below ∼100°K in Ge whose bulk resistivity has been made greater than ${10}^3$ to ${10}^5$ ohm-cm by the addition of Au. A new permanent-magnet apparatus for measuring the Hall effect in semiconductors at low temperatures is described. The results of measurement of the Hall effect as a function of temperature in Ge samples containing grain boundaries of known orientation are given. A peak in the Hall coefficient observed in some samples is discussed in terms of a crude model. Preferential conduction along grain boundaries also occurs in high-resistivity Fe-doped Ge, but has not been observed in crystals containing coherent twin boundaries. A modification of Bardeen's theory of surface states is used in an attempt to account for the existence of the grain-boundary conduction phenomenon.