Optical absorption in PECVD deposited thin hydrogenated silicon in light of ordering effects

Abstract

Abstract:We report results obtained from measurements of optical transmittance spectra carried out on a series of silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane diluted with hydrogen. Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to microcrystalline hydrogenated silicon (µc-Si:H). Spectral refractive indices and absorption coefficients were determined from transmittance spectra. The spectral absorption coefficients were used to determine the Tauc optical band gap energy, the B factor of the Tauc plots, E 04 (energy at which the absorption coefficient is equal to 10 4 cm −1 ), and the Urbach energy as a function of the hydrogen dilution. The results were correlated with microstructure, namely volume fractions of the amorphous and crystalline phase with voids, and with the grain size.

Quantum Size Effects in a Si:H Films Prepared by PECVD with Different Hydrogen-Diluted Silane

“…Optical properties of the films (optical band-gap energies, refractive indices, extinction coefficients) were calculated using spectral measurements carried out on a spectrophotometer Specord 210 working in the range of 190-1100 nm. Spectral refractive indices and extinction coefficients of the films were extracted from the measured UV-Vis spectra using a Delphi-based program based on an optimisation procedure using genetic algorithm [4,5].…”

“…This observation is in a good agreement with the XRD results found for the same samples. The confinement effect on the band-gap arises from the kinetic energy of the electron-hole pairs separated by a distance of the QD dimension "a" and the Coulomb interaction [4]. The values of 140 5th FORUM ON NEW MATERIALS PART C…”

“…Various mechanisms are discussed to be responsible for unusual behaviour of nanostructures, e.g. bond-order-length-strength correlation [4]. The size-dependent band-gap makes a material attractive for optical absorptionbased applications.…”