Grain Boundary States in Silicon and Germanium

Abstract

Bicrystals of n- and p-type silicon and p-type germanium with relatively large tilt angles are grown from the melt, while some bicrystals of silicon are prepared by floating zone technique. From measurements of the photoresponse and the current-voltage characteristics across the grain boundary and the Hall effect for current flow along the grain boundary, it is concluded that the grain boundaries of p- and n-type silicon bicrystals are of n- and n- type respectively. Similar measurements are performed on p- type germanium bicrystals. It is shown that the grain boundary states of silicon bicrystals are located above the middle of the forbidden band, and pick up both electrons and holes, independently of the oxygen content. The boundary states of germanium bicrystals, lying below the middle of the forbidden band, accept only the electrons exclusively and form a p p ⁺ p structure at the grain boundary at 300°K.