CHARGED GRAIN-BOUNDARIES IN GERMANIUM

The equilibrium properties of a low angle tilt boundary are discussed on the assumption that the boundary states form a partially filled band with a neutral level located in the lower half of the energy gap. The electrostatic energy and the entropy stored in the screening layer are major factors in determining the occupancy of the boundary levels. The screening effects depend strongly on temperature and the doping conditions: in n type germanium a depleted layer is found at low temperatures, with a gradual evolution towards an inversion layer in the high temperature range. In p type germanium the depleted layer transforms into an accumulation layer through a neutral temperature. The barrier effect is much stronger in n than in p type germanium, in agreement with available experimental results.