Influence of a Thickness and Percentage of Ge in Optical Properties of Thin Films of Si1-xGex Grown by LPCVD

Abstract

Optical properties of Si1-xGex thin films obtained by LPCVD, with different thickness and percentages of Ge are investigated in this work. Raman spectroscopy was employed for the determination of Ge percentage (x) and strain (ε) present on the films, using equations that involve the frequencies of Si-Si, Si-Ge and Ge-Ge Raman vibrational modes. From these calculations, an increase in the percent of Ge is observed with the rise of time of deposition. The refractive index of each film was determined by Ellisometry, where an abrupt increase of this parameter is detected for films of lower thickness. This result could be due to the quantum confinement effects as a consequence of the thickness of these films, which is comparable with the excitonic Bohr diameter of Ge. The best result was obtained to the film Si0.63Ge0.37 grown at 30s with a refractive index n= 3.141 for λ= 632.9 nm, thickness of 62.7 nm and a density of nanoparticle about 1.0x1010 cm-2 with an average size of ~ 47 nm.