Electrical and structural studies of copper and nickel precipitates in a Σ=25 silicon bicrystal

Abstract

Deep-level transient spectroscopy measurements of electronic defect states in a coincidence Σ=25 grain boundary (GB) in silicon have been performed after quenching of heat-treated samples (900 °C, 2 h) containing copper and/or nickel. These elements are usually suspected to be nonintentionally contaminating impurities. The special care supplied to get processed samples free from transition-metal impurities (particularly copper) has led to the measurement of a continuous distribution of boundary levels between Ec−0.20 eV and Ec−0.38 eV which shift toward deeper energies (between Ec−0.25 eV and Ec−0.42 eV) with a gradual increase of the copper content. The heavily contaminated samples with Cu or with both Cu and Ni exhibit a single interface trap at Ec−0.54 eV. According to transmission electron microscopy (TEM) and energy-dispersive x-ray (EDX) analyses, as well as comparable data reported earlier, this interface state seems characteristic of copper precipitates obtained by quenching from 900 °C; however, the incorporation of nickel in a ‘‘copper-free’’ bicrystal has been found to result in an almost discrete boundary level at Ec−0.50 eV. From TEM, EDX, and electron-diffraction investigations, the corresponding precipitates were geometrically shaped, intersecting the GB plane, and identified as two types (A and B) of NiSi2 silicide.