Refractive index and hygroscopic stability of AlxGa1−xAs native oxides (original) (raw)
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Optical constants of (Al0.98Ga0.02)xOy native oxides
Applied Physics Letters, 1998
We report the optical constants of oxidized crystalline and low-temperature-grown (LTG) Al0.98Ga0.02As films, as determined by variable angle spectroscopic ellipsometry. Data were acquired at three angles of incidence over 240–1700 nm and fitted to a Cauchy dispersion function. For oxidized crystalline material, we observe a variation in the real index of ±0.5% for layer thickness variations of ±6%. We show that upon oxidation, LTG material can expand by >25% while crystalline material contracts by <2%. Atomic force microscopy analysis indicates thickness-dependent variations in the oxide microstructure. Additionally, an optical scattering loss of 2.1×10−4%/pass is calculated based on surface roughness measurements for a thin layer of oxidized crystalline material.
Systematic measurement of AlxGa1−xN refractive indices
Applied Physics Letters, 2001
Dispersion of the ordinary and extraordinary indices of refraction have been measured systematically for wurtzitic Al x Ga 1Ϫx N epitaxial layers with 0.0рxр1.0 throughout the visible wavelength region. The dispersion, measured by a prism coupling waveguide technique, is found to be well described by a Sellmeier relation. Discrepancies among previous measurements of refractive index dispersion, as a consequence of different growth conditions and corresponding band gap bowing parameter, are reconciled when the Sellmeier relation is parameterized not by x but by band gap energy.
Refractive index study of AlxGa1−xN films grown on sapphire substrates
Journal of Applied Physics, 2003
A prism coupling method was used to measure the ordinary (no) and extraordinary (ne) refractive indices of AlxGa1−xN films, grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) on sapphire, at several discrete wavelengths from 442 nm to 1064 nm. In addition, spectroscopic transmittance and reflectance, correlated with the prism coupling results, were used to measure no as a continuous function of wavelength between the band gap of each sample (255 nm to 364 nm, depending on Al fraction) and 2500 nm. The Al mole fractions (x), determined by energy dispersive x-ray spectroscopy (EDS), were x=0.144, 0.234, 0.279, 0.363, 0.593, and 0.657 for the HVPE-grown samples, and x=0.000, 0.419, 0.507, 0.618, 0.660, and 0.666 for the MOCVD-grown samples. The maximum standard uncertainty in the EDS-determined value of x was ±0.02. The maximum standard uncertainty in the refractive indices measured by prism coupling was ±0.005 and a one-Sellmeier-term equati...
Modeling the optical constants of AlxGa1−xAs alloys
Journal of Applied Physics, 1999
Extension of Adachi's model with a Gaussianlike broadening function instead of a Lorentzian one is used t o model the optical dielectric function of the alloy AI,Gal-,As. Gaussian-like broadening is accomplished by replacing the damping constant in the Lorentzian line shape with a frequency dependent expression. In such a manner, the comparative simplicity of analytic formulae of the model is preserved, while the accuracy becomes comparable to more intricate models, and/or models with a significantly greater number of parameters. The employed model describes accurately the optical dielectric function in the spectral range from 1.5 t o 6.0 e V in the entire alloy composition range. Relative rms error obtained for the refractive index is below 2.2% for all compositions.
Systematic measurement of Al[sub x]Ga[sub 1−x]N refractive indices
Applied Physics Letters, 2001
Dispersion of the ordinary and extraordinary indices of refraction have been measured systematically for wurtzitic Al x Ga 1Ϫx N epitaxial layers with 0.0рxр1.0 throughout the visible wavelength region. The dispersion, measured by a prism coupling waveguide technique, is found to be well described by a Sellmeier relation. Discrepancies among previous measurements of refractive index dispersion, as a consequence of different growth conditions and corresponding band gap bowing parameter, are reconciled when the Sellmeier relation is parameterized not by x but by band gap energy.
Nature and growth of anodic and thermal oxides on GaAs and AlxGa1−x As
Corrosion Science, 1999
This paper considers the nature of anodic and thermal oxides on GaAs and Al x Ga 0−x As\ with x 9[1\ 9[4 and 9[7[ Anodic oxides were produced in NH 3 H 1 PO 3 solution and thermal oxides formed in O 1 at 499>C[ The chemical composition of the oxides "¾29 nm thick# has been evaluated using secondary ion mass spectrometry "SIMS#\ complemented by X!ray photo! electron spectroscopy "XPS# and other techniques[ Anodic oxides on GaAs comprise both Ga 1 O 2 and As oxides[ For Al x Ga 0−x As\ Ga is enriched in the outer part of the _lm due to Ga! phosphate formation[ The higher the Al content in the oxide\ the less Ga!phosphate is present[ Al is enriched at the inner interface\ the amount increasing with increasing Al content in the substrate[ These anodic _lms basically comprise a three!layer structure] Ga phosphate]Ga:As oxide]Ga:As:Al oxide[ Thermal oxides on GaAs consist almost entirely of Ga 1 O 2 \ with a small As enrichment at both the gasÐoxide and the oxideÐsubstrate interfaces[ This is also the case for thermal _lms on Al 9[7 Ga 9[1 As\ but now the main components of the _lm are Ga 1 O 2 and Al 1 O 2 [ Unlike anodic oxides\ thermal oxides on both Al x Ga 0−x As and GaAs are stable in the air and do not change perceptibly over a period of several months[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
Journal of Applied Physics, 2000
The refractive indices of Al x Ga 1Ϫx As epitaxial layers (0.176рxр1) are accurately determined below the band gap to wavelengths, Ͻ3 m. The layers are grown on GaAs substrates by molecular beam epitaxy metal organic and chemical vapor deposition with thicknesses ranging from 4 to 10 m. They form improper waveguide structures with the GaAs substrate. The measurements are based on the excitation of the improper waveguide modes with grating couplers at 23°C. The refractive indices of the layers are derived from the modal propagation constants in the range of 730 nmϽϽ830 nm with an estimated uncertainty of ⌬nϭ5ϫ10 Ϫ4 . The temperature coefficient of the refractive index is investigated in the same spectral range. From the effective indices of the TE and TM modes, we derive the strain-induced birefringence and the elasto-optic coefficients. High-resolution x-ray diffraction is used to determine the strain of the layers. The layer compositions are obtained with inductively coupled plasma atomic emission spectroscopy. The measurement range of the refractive index is extended from the direct gap to Ͻ3 m by observing the Fabry-Pérot interference fringes of the transmission spectra of isolated layers. The measured values of the refractive index and the elasto-optic coefficient are compared to calculated data based on semiempirical models described in the literature. Published data of the index of refraction on GaAs, AlAs and GaP are analyzed to permit the development of a modified Sellmeier approximation. The experimental data on Al x Ga 1Ϫx As can be fitted over the entire composition range 0рxр1 to provide an accurate analytical description as a function of composition, wavelength, and temperature.
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The Refractive Index and Effective Band Gap variation of wurzite AlXGa1-XN with respect to temperature with bowing parameter b=1.3±0.2 eV, have been studied. Refractive index found to i ncrease for all compositions and its rate of increase is more in the vicinity of band gap. A set of values for model parameters C(x, T) and A(x, T) were obtained for different compositions and temperatures. The variations of C(x, T) and A(x, T) with compositions were found to be stronger than their corresponding temperature variations. The variation in dielectric function expressed in terms of C(x, T) and A(x, T) with respect to temperature and composition have been studied. It is found that dielectric function is nonlinearly increasing with increasing temperature and composition. This work enables us to calculate refractive index of GaN and AlGaN alloys at any desired temperature and hence to predict properties of GaN based waveguides at elevated temperatures.
TEM characterization of oxidized AlGaAs/AlAs nonlinear optical waveguides
Journal of Physics D: Applied Physics, 2010
The internal interfaces of multilayer Al x Ga 1-x As/AlAs nonlinear optical waveguides are investigated by high-angle annular-dark-field and energy-filtered scanning transmission electron microscopy, before and after partial wet oxidation of AlAs layers. Via a simple phenomenological model, the corresponding roughness parameters allow predicting the scattering-induced waveguide optical losses, which are in reasonable agreement with the experimental value of 0.5 cm-1. We also find that Al x Ga 1-x As layers adjacent to oxidized AlAs tend to be oxidized through the interfaces, even for low Al fraction, with typical oxidation depths of 9 nm for x=0.7 and 2 nm for x=0.