High-accuracy, midinfrared (450 cm-1≤ω≤4000 cm-1) refractive index values of silicon -: art. no. 123526

The real and imaginary parts of the refractive index, n(omega) and k(omega), of silicon were measured as a function of photon frequency omega using Fourier transform infrared (FTIR) transmission spectral data. An accurate mechanical measurement of the wafer's thickness, t, was required, and two FTIR spectra were used: one of high resolution (Delta omega=0.1 to 0.5 cm(-1)) yielding a typical channel spectrum (Fabry-Perot fringes) dependent mainly on t and n(omega), and one of low resolution (Delta omega=4.0 cm(-1)) yielding an absorption spectrum dependent mainly on t and k(omega). A procedure was developed to first get initial estimates for n(omega) for the high-resolution spectrum and then calculate k(omega) from the faster low-resolution spectrum with minimal measurement drift. Then both initial n and final k values were used together as starting point data for a fit to the high-resolution spectrum. A previously derived transmission formula for a convergent incident beam was used for the fit. The accuracy of n(omega) determined using this procedure is mostly dependent upon the measurement error in the sample thickness t and k(omega) is dominated by the accuracy of the absolute transmission values obtained from a sample-in and sample-out methods. Our results are compared with previously published values for n(omega) and k(omega) in the 450-4000-cm(-1) spectral region. The reported uncertainty in n(omega) is +/- 10(-4) absolute, a factor of 10 better than published values. The values of n(omega) range from 3.4400 at 4000 cm(-1) (lambda=2.5 mu m) to 3.4169 at 450 cm(-1) (lambda=22.222 mu m). The k(omega) values had a standard deviation of <=+/- 3% and are in good agreement with previous measurements. (c) 2005 American Institute of Physics.