Determination of AlAs optical constants by variable angle spectroscopic ellipsometry and a multisample analysis

Abstract

Using variable angle spectroscopic ellipsometry, optical constants for AlAs (1.4-5.0 eV) are presented which are simultaneously compatible with measured data from four different samples. The below-gap index values are compatible with published prism measured values. The second derivative spectrum are compatible with published values above the direct band gap. The AlAs spectra is Kramers-Kromg self-consistent over the measured range and is compatible with published values from 0.6 to 1.4 eV. The optical constants for thin ((50 A) GaAs caps on AlAs are shown to be different from bulk GaAs values and require special consideration when fitting ellipsometric data. For the thin GaAs caps, the Et and E,+A, critical-point structure is shifted to higher energies as previously observed for GaAs quantum wells. Bulk AlAs optical constants are shown to be different from those of a thin (-20 A) AlAs barrier layer embedded in GaAs. The thin barrier layer exhibits a highly broadened critical-point structure. This barrier broadening effect (AlAs) and the thin cap shifting effects (GaAs) have implications for in situ growth control schemes which make use of the E, and E, +A, critical-point region. 0 1995 American Institute of Physics.

Determination of the optical dispersion in ferroelectric vinylidene fluoride (70%)/trifluoroethylene (30%) copolymer Langmuir–Blodgett films

“…To further reduce the correlation among the parameters in the fitting process and improve accuracy, a multi-sample data analysis technique was used. 17,[20][21][22] This technique fits the VASE data ͑ , ͒ and ⌬͑ , ͒ for samples with the same substrate properties, but different thickness d, and assumes that the optical constants n( ) and k( ) are independent of thickness ͑and that the films are uniaxial͒. As will be shown below, this is a good approximation for the copolymer LB film with the thickness ranging from 5 to 125 ML.…”

“…The mean square difference between the experimental data and the model-generated data were minimized by adjusting the model parameters. 20 The optical properties of the Si substrate ͑with 4.3 nm native oxide in this case͒ were independently calibrated by the spectroscopic ellipsometry before film deposition and fixed for the sample fitting procedure to reduce the number of adjustable parameters, so only the properties of copolymer LB films were varied. In fitting the data, we further assumed that the LB film was optically uniaxial.…”

Dielectric function of amorphous tantalum oxide from the far infrared to the deep ultraviolet spectral region measured by spectroscopic ellipsometry

“…45 are often utilized. 43,46 Separate MDFs are employed in this work for the tantalum oxide IR and NIR-VUV dielectric function spectra, respectively. For the NIR-VUV data a general parametric functional model based on the Kim and Garland approach [47][48][49] is used to describe and fit ⑀ Ta for amorphous tantalum oxide.…”

“…42,43 The random experimental errors ( i ⌿ , i ⌬ ) were appropriately propagated into the error bars on the fit parameters. 45 are often utilized.…”

Modeling the optical constants of AlxGa1−xAs alloys

“…There have also been several experimental studies of pure materials-GaAs 2,3 and AlAs. [4][5][6][7] However, the significant shortcomings of these experimental studies are that the data are not expressed in terms of continuous analytical functions of the electronic energy gaps and the alloy composition x. Therefore, there is a requirement to model the experimental data with an analytical model.…”