Silicon (si) Revisited (1.1–3.1 ev)

At the room temperature, the extinction coefficient, k, of nominally pure, single-crystal silicon (Si) increases from less than 10-6 at the onset of the indirect transition to almost 1 at 370 nm. The real part of the index of refraction, n, of Si at room temperature varies by less than a factor of 2 over the same spectral range. It is noted that transmission measurements are the most accurate way to determine k ≪ 1, but they require thin samples for wavelengths less than about 550 nm. More accurate values of k can be deduced from the reflectance or ellipsometric measurements below this wavelength. Only reflectance and ellipsometric measurements can be used to measure n except at the longest wavelengths of this spectral region because of the large values of the absorption coefficient over most of the region. All of the measurements are carried out at nominal room temperature. Single-crystal material that precludes extrinsic effects in the spectral region of measurements is essentially used.