Electrical Conduction Along the Tilt and Twist Grain Boundaries in n-Type Germanium

Abstract

The resistivity and Hall coefficient for current flow along the grain boundary of both tilt and twist Ge bicrystals with various misfit angles and orientations are measured as a function of temperature between 70°K and 250°K. Bulk Ge is doped by Sb and its resistivity is in the range of 3 to 40 Ω cm at 295°K. Twist grain boundary has a p-type property similar to that observed with the tilt one. This possibility is discussed by considering the broken bonds in screw dislocations. For small misfit angle the results show that the energy level of an acceptor type is located at about 0.14 ev above the valence band in both types of boundary. With increasing misfit angle, the energy level tends to approach the valence band and be broadened similarly to the case of impurity band conduction. A model such as two clean surfaces are contacted facing each other is used with the modification of energy level to account for the grain boundary conduction phenomena. By using the low mobility of carrier in an acceptor-like band and in the disturbed region, the temperature dependence of Hall mobility is discussed.