Spectroscopic Ellipsometer is employed to study the optical properties (including complex refractive index and bandgap) of pristine and doped AlN (Ti and Cr) films as a function of doping ...concentration and temperature (273 K–573 K). Pristine AlN, Al1−xTixN (x = 1.5, 3 and 4 at%) and Al1−xCrxN (x = 2, 4 and 6 at%) films are grown on Si(100) substrates using magnetron sputtering technique. The crystal structure and chemical composition of the as grown films are analyzed using Grazing Incidence X-ray Diffraction (GIXRD) and X-ray Photoelectron Spectroscopy (XPS) techniques, respectively. The optical properties of Ti, Cr doped AlN films at a wider range of energies as well as different ambient temperatures are reported. To determine the complex refractive indices, the measured ellipsometric parameters Is and Ic are fitted using a five layer model with Lorentz oscillator dispersion relation. As far as the bandgap region is concerned, both the real and imaginary parts of the refractive index show significant changes near the bandgap. It is observed that, the real part of refractive index of AlN increases monotonically with the increase in Ti doping and opposite in Cr doping. The extinction coefficient is relatively larger for Cr-doped AlN compared to Ti-doped AlN films. With the increase in doping concentration, the bandgap is found to decrease rapidly for Cr-doped AlN in comparison to Ti-doped AlN films. Additionally, a significant change in the complex refractive index of doped AlN films is observed with temperature.
Display omitted
•Spectroscopic Ellipsometry (SE) technique is used to investigate the optical constants of Ti and Cr doped AlN films.•The refractive index (n) of doped-AlN increases monotonically with the increase in Ti doping and decreases for Cr doping.•A significant increase in the extinction coefficient (k) of doped AlN films is observed with the increase in temperature.•With the increase in doping concentration, the bandgap decreases rapidly for Cr-doped AlN films, unlike Ti-doped AlN.
This paper reports the temperature effects on the optical properties of metalorganic vapour-phase epitaxy (MOCVD) grown c-axis oriented AlN epilayer thin film studied by in-situ high-temperature ...spectroscopic ellipsometry. The crystal structure and the quality of the grown AlN epilayer film are analyzed using X-ray Diffraction and rocking curve techniques, respectively. Modelling of the ellipsometric data revealed that the uniaxial anisotropic refractive indices of the c-axis oriented film in the directions n‖ and n⊥ increased from 2.50 to 2.59 and 2.32 to 2.37, respectively with the increase in temperature from 223 to 573 K. The thermo-optic coefficients were evaluated to be around 10−5. Nano-mechanical characterization of this film showed an average hardness of 19.4 GPa at ambient temperature, which is higher than a-axis oriented AlN film. The average surface free energy of the synthesized film as evaluated from contact angle measurements is reported to be around 36.22 ± 0.64 mN/m. These results are highly relevant for a better understanding of c-axis oriented AlN-based materials in high-temperature ultraviolet optical devices.
•Spectroscopic Ellipsometry technique is used to investigate the temperature-dependent uniaxial anisotropic optical constants of c-axis AlN film.•Refractive indices along parallel and perpendicular to the c-axis of AlN increase from 2.50 to 2.59 and 2.32 to 2.37, respectively with an increase in temperature from 223 to 573 K.•Nano-mechanical characterization of the c-axis AlN film shows high hardness than that of the a-axis oriented AlN film.•The surface free energy of the film as evaluated from contact angle measurements is around 36.22 ± 0.64 mN/m.
► Chemical and optical properties of the interface between a Cu(In,Ga)Se2 (CIGSe) absorber and the Mo back contact are investigated. ► After the lift-off of the CIGSe absorber from the Mo layer, ...X-ray photoelectron spectroscopy (XPS) and ellipsometry are performed on these interfaces. ► The calculated optical reflectivity of the real Mo/CIGSe interface was found to be quite low. ► The enhancement of light absorption in ultrathin absorbers down to 100nm by using alternative, highly reflective back contacts is discussed.
Chemical and optical properties of the interface between a coevaporated Cu(In,Ga)Se2 (CIGSe) absorber thin film and the Mo back contact are investigated with the objective to reduce markedly the thickness of CIGSe layers from two microns down to about 100nm. First a mechanical lift off technique allowed to separate Mo and CIGSe layers and perform X-ray photoelectron spectroscopy (XPS) and elipsometry studies on as prepared surfaces. On the Mo side small amounts of In and Ga are observed together with the formation of an MoSe2 layer. There is no evidence of the presence of Cu. On the opposite CIGSe side a clear depletion of Cu together with an enrichment of Ga is evidenced. There is no evidence of Mo. Optical reflectivity of the interface CIGSe/Mo is studied by ellipsometry showing a low reflectivity of the interface attributed to the formation of MoSe2 layer. The enhance light absorption in ultrathin absorbers using alternative, highly reflective back contacts are finally discussed.
A methodology for evaluating the precision of ellipsometrically determined model parameters (such as thickness) as a function of the measured data set (wavelength(s) and angle(s) of incidence) is ...presented and experimentally validated. This methodology is used to determine acceptable angle of incidence ranges for ellipsometric measurements and to study the merits of including multiple angles in the data set. Simulations and experimental results are presented for rotating analyzer ellipsometer and rotating compensator ellipsometer systems, using examples of thin and thick films on silicon substrates. A rigorous noise model is used to predict the ellipsometric measurement noise and Monte Carlo simulations are used to determine the parameter precision for a given data set.
We use a rigorous electromagnetic code to investigate the differences between the zeroth-order cross-polarization reflection coefficients in highly conducting metallic gratings with asymmetric ...profile. This study results of interest from a practical point of view due to its possible applications as a technique to detect gratings asymmetries. Numerical results in holographic gratings made of gold with asymmetric profiles are presented.
