Optical characteristics of intrinsic microcrystalline silicon

Abstract

We studied the optical properties of intrinsic microcrystalline silicon ( c-Si:H) deposited by very high frequency plasma-enhanced chemical-vapor deposition system at different silane concentrations ͑SC͒ by spectroscopy ellipsometry and photothermal deflection spectroscopy. The bulk property of the samples was probed because the impact of the surface layer was significantly reduced by mechanical polishing. At high SC, we extracted the optical characteristics of the disordered part by assuming a superposition of ideal c-Si and mathematically generated amorphous function. At low SC, we studied the reason for a large deviation of absorption coefficient in the energy range between 1.6 and 3.2 eV from the value predicted by effective medium theory. We considered the scattering loss by the inhomogeneity of c-Si:H and introduce the dense medium radiative transfer formalism to an optical scattering simulation. We simulated the Stokes vector of pand s-polarized light at oblique incidence. From this formalism, we could predict depolarization of p and s wave by scattered incoherent light. Further, we also suggested strain effect as the second possible reason for the enhanced absorption near the onset of the indirect transition in highly crystalline c-Si:H.

Thin-film silicon solar cells with efficient periodic light trapping texture

“…Therefore, the optical properties of c-Si: H cells with periodically textured substrates and numerous texture designs are studied by numerical modeling using the optical constants of c-Si: H determined by optical characterization of individual layers. 17 The diffraction of the light incident on the grating coupler leads to a prolonged absorption path within the solar cell; because with increasing diffraction order k the absorption path increases ͓sin͑ + ͒ = k / Pn͔. denotes the vacuum wavelength, the angle of diffraction, the angle of incidence, P the period size of the grating coupler, and n denotes the refractive index of the material in which the transmitted, diffracted light propagates.…”

Advanced light trapping management by diffractive interlayer for thin-film silicon solar cells

“…The optical properties of a-Si: H, c-Si: H, and the transparent conducting oxide ͑TCO͒ ZnO are determined by characterization of individual layers. 7 Illumination is performed by a plane wave boundary condition at the top of the multilayer cell under normal incidence and circular polarization. The absorption in each layer is calculated and the quantum efficiency and maximum short circuit current density are computed assuming perfect collection of generated carriers, i.e., every absorbed photon generates an electron-hole pair that contributes to the photocurrent.…”

Microcrystalline silicon p–i–n photodetectors for telecommunications and photovoltaic applications

“…The larger crystallinity of the V oc ¼ 481 mV sample is evident from the shorter wavelength at which the onset of interference occurs. In this case the fringe amplitude is larger because of the lower absorption of large-grain silicon compared to fine grain microcrystalline silicon in the range 1.6-3.2 eV [5], due to depolarization and scattering at grain boundaries [7]. We stress that the large crystallinity of the V oc ¼ 481 mV sample is observed with a 50% large-grain fraction in the initial (200 nm) stage of the growth.…”