Optical properties of SiGe single crystals grown by liquid phase diffusion

In this article, we present measurements for the pseudo-optical functions of germanium-rich SixGe1-x (0.000<x<0.100) single-crystals(grown by Liquid Phase Diffusion; LPD) using spectroscopic ellipsometry and photo reflectance techniques in the energy range of 1.72–3.20 eV. The E1 interband transition energies are obtained from numerically differentiated optical spectra for various crystal compositions. It was shown that the values of E1 interband transition energy determined by both the ellipsometric and photo reflectance measurements for germanium-rich SixGe1-x single-crystals are in agreement with those of bulk SiGe crystals reported in the literature[21–24].The interband transition energies are found to be in the range of 2.100 and 2.215 eV for the composition values of 0.000<x0.100. The surface morphology of the crystals assayed via atomic force microscopy shows fibrous surfaces with the average grain size of 250 nm. The measured root-mean-square (rms) roughness and maximum height are in the range of 3.78–5.40 and 32.42–67.84 nm, respectively, with increasing germanium composition

Confined LO phonon limited free carrier absorption in quantum well wires

The theory of free-carrier absorption is given for quantum well wire for the case where the carriers are scattered by confined longitudinal-optical (LO) phonons and the radiation field is polarized along the length of the wire. Both the multisubband structure and confined phonon modes are considered together. The free carrier absorption coefficients are calculated taking into account all possible LO phonon modes as well as all possible electron intersubband transitions. The results show that the absorption coefficient decreases with increasing the photon frequency and decreases with temperature. It was found that in quantum wire the electron-optic phonon interaction give a greater contribution to the absorption than the electron-confined LO phonon interaction. The results are interpreted in terms of confined LO phonons-assisted transitions between size quantized subbands