Korngrenzenstruktur und Ladungsträgertransport in Halbleiterkristallen

Abstract

The structural character of boundaries or interfaces between two perfect crystals of different orientation but equal chemical composition defines the behavior of grain boundaries with respect to carrier transport. The amount of misfit in the grain boundary zone, as well as the amount of energy stored by elastic deformation, defines the electrical properties. The number of free carriers (electrons) in boundary states increases with the cross-potential applied, while positive space charge regions build up on both sides of the boundary. The boundary zone itself has p-type character and becomes more conductive when the number of electrons bound to the dangling bonds increases. Grain boundary zones may be as thick as a few tenths of a mm. Extremely small zones are formed by disturbed twins. Two and three probe measurements on such bicrystals have been made in order to study the carrier transport phenomena. High current multiplication due to carrier density misfit and gate action in the case of opposite polarization have been found. In addition, contacts were plated to boundary-zones; and modulation through the bulk material, as in a NPN-junction, was studied. Here current multiplication can reach high values even in a base-to-ground connection. Since those electrons bound to a grain boundary interface by a cross potential may be present only in the form of excitons, in the field of their dangling bonds before adjustment, their time constants for recharging processes might be very short such that it is probable that high frequency response is improved. Basic elements and consequences of the developed theory and the correlation between boundary stress field and carrier transport are outlined.