11,902 research outputs found
Analytical Model for the Optical Functions of Indium Gallium Nitride with Application to Thin Film Solar Photovoltaic Cells
This paper presents the preliminary results of optical characterization using
spectroscopic ellipsometry of wurtzite indium gallium nitride (InxGa1-xN) thin
films with medium indium content (0.38<x<0.68) that were deposited on silicon
dioxide using plasma-enhanced evaporation. A Kramers-Kronig consistent
parametric analytical model using Gaussian oscillators to describe the
absorption spectra has been developed to extract the real and imaginary
components of the dielectric function ({\epsilon}1, {\epsilon}2) of InxGa1-xN
films. Scanning electron microscope (SEM) images are presented to examine film
microstructure and verify film thicknesses determined from ellipsometry
modelling. This fitting procedure, model, and parameters can be employed in the
future to extract physical parameters from ellipsometric data from other
InxGa1-xN films
Ion-implantation induced anomalous surface amorphization in silicon
Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model
Direct Observationof DegenerateTwo-Photon Absorption and Its Saturation in WS2 and MoS2 Monolayer and Few-Layer Films
The optical nonlinearity of WS2, MoS2 monolayer and few-layer films was
investigated using the Z-scan technique with femtosecond pulses from the
visible to the near infrared. The dependence of nonlinear absorption of the WS2
and MoS2 films on layer number and excitation wavelength was studied
systematically. WS2 with 1~3 layers exhibits a giant two-photon absorption
(TPA) coefficient. Saturation of TPA for WS2 with 1~3 layers and MoS2 with
25~27 layers was observed. The giant nonlinearity of WS2 and MoS2 is attributed
to two dimensional confinement, a giant exciton effect and the band edge
resonance of TPA
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