EBIC studies of grain boundaries

REBIC is a powerful technique for the study of defects, especially grain boundaries (GBs), in ill developed, high-resistivity (semi-insulating) materials. Ideas for modelling GB REBIC contrast have been proposed but neither quantitatively developed nor applied to details of experimental contrast. The model of two Schottky barriers back to back for charged boundary (peak and trough) contrast and the high-resistivity boundary layer model for terraced contrast are spelled out in further detail here. They are then applied to observations on high-resistivity polycrystalline ZnSe. The models suffice to account for most features observed. The relative doping density on either side of boundaries can be determined by measuring the barrier width as a function of the reverse bias. The sign of the charge on boundaries can be deduced by observing whether the peak or trough occurs on the dark terrace side of a boundary. Observations of the reversal of peak and trough contrast along the length of boundaries indicate that both - very and + very charged regions occur. The asymmetry of the peaks and troughs at many terraced boundaries can be accounted for by the biasing of the Schottky barriers by the voltage drop across the barrier layer due to the REBIC current. The significance of the additional information obtainable by (i) the crystallographic characterization of boundaries by the EBSP technique and (ii) studies of the temperature dependence of REBIC contrast is discussed.