Electrical measurement of the dopant segregation profile at the grain boundary in silicon bicrystals

Abstract

The paper presents a new method of determining the dopant concentration profile at the grain boundaries in polycrystalline semiconductors, based on high-frequency capacitance and dc conductance measurements. The method takes advantage of the electrostatic potential barrier associated with charged grain boundaries, and resembles, in that respect, the well-known junction capacitance technique of dopant profiling in semiconducting single crystals. As an example of application, the doping profile has been determined for the Σ=25 twin boundary in n-type (phosphorus-doped) and p-type (boron-doped) silicon bicrystals. The dopant distribution has been found, in both types of samples, very nearly homogeneous on a range of a few microns about the grain-boundary plane. This has been verified, in the case of the boron-doped bicrystals, by a secondary ion mass spectroscopy measurement of the boron concentration profile at the boundary. Annealing treatments on the n-doped bicrystals induce a slight segregation of phosphorus at the boundary. The form of the doping profile, as given by the electrical measurements, is discussed on the basis of McLean’s model of impurity segregation. The binding energy of phosphorus at the boundary is estimated on the order of 0.6 eV, comparable in order of magnitude to the values obtained by microanalytical studies of the dopant segregation at the boundaries in microcrystalline silicon.