A technique for characterizing surface recombination in silicon wafers based on thermal-emission measurements

A noncontact technique for the measurement of the surface-recombination rate in silicon wafers is suggested. A wafer under study is excited optically in the spectral region of intrinsic absorption, and the excitation-wavelength dependence of the power of the wafer thermal emission beyond the intrinsic-absorption edge is examined. The surface-recombination rate is determined from the ratio of intensities of the wafer thermal emission in the wavelength range 3–5 μm recorded under excitation with two laser diodes with wavelengths of 863 and 966 nm. Wafers subjected to different surface treatments were tested; at 230°C, rates on the order of 10⁴ cm/s were measured after mechanical polishing and 10³ cm/s after etching in CP-4A etchant. The applicability of the method is discussed, and the measurement error as a function of the wafer and light-source parameters is considered.