Optical metrology of thickness and indium composition of epitaxial InxGa1−xAs layers on Si substrates
An optical metrology solution using a Spectroscopic Ellipsometer (SE) tool has been demonstrated to monitor the thickness and indium composition of InxGa1-xAs layers on Si substrates for III-V compound semiconductor channel devices. Fundamentally, the SE tool is based on light interference and phase shift effects corresponding to individual material properties. A wide range of wavelengths (190 ~ 840nm) of the SE spectra is used to collect elliptically polarized light and for dispersion model characterization to float n and k values at each wavelength. The SE data for InxGa1-xAs and indium composition is quantified using TEM (Transmission Electron Microscopy) and RBS (Rutherford Backscattering Spectrometry) showing excellent correlation. In the range of 190nm to 840nm wavelengths SE is able to provide InxGa1-xAs layer thickness through post data processing using InxGa1-xAs/GaAs layer thickness with surface roughness consideration. Reducing the surface roughness is expected to enable more accurate and higher intensity of elliptically polarized light from films so that the best film model can be applied to float n and k values. Indium composition of the InxGa1-xAs layer is quantified by dispersion (n and k) values extracted from a specific wavelength. In this work, the n value of InxGa1-xAs/GaAs film stack at 219nm shows excellent proportional relationship with RBS data on three different indium compositions, while k value at 248nm shows excellent inverse relationship. This is a promising solution to evaluate critical growth parameters such as indium composition and to offer detailed and immediate feedback on the deposition process. This solution can be extended to other compound materials - characterizing thickness and composition by correlating n and k values for each wavelength.
RELATIONSHIP BETWEEN SURFACE MORPHOLOGY AND STRAIN RELAXATION DURING GROWTH OF INGAAS STRAINED LAYERS
The relationship between the surface morphology and strain relaxation is explored in strained InxGa1−xAs layers grown on GaAs by molecular beam epitaxy. In situ light scattering, detected simultaneously along [110] and [110], reveals an asymmetric surface roughening which is consistent with ex situ scanning force microscopy. Transmission electron microscopy shows that strain relaxation by misfit dislocation formation occurs before the surface roughening is detected, for In0.18Ga0.82As films grown at 490 °C.
Quantitative and qualitative relationship between swirl burner operatingconditions and pulverized coal flame length
Abstract Currently, there are used in power plants two types of burners to combustion the pulverized coal: jet burners and swirl burners. Most of the published works in the field of analysis of burners operating conditions are related to jet burners and are limited to initial region of the flame at the outlet of the burner. For jet burners an offset between the burner outlet and the flame beginning point could be analyzed. In the case of swirl burners with the pre-mixing diffuser chamber an offset between flame ignition point and burner outlet is usually not visible. Because already in the pre-mixing diffuser chamber of swirl burner occurs the ignition of coal-dust together with oxidant-gas cloud and thereby the formation of the flame. Therefore, the analysis of operating conditions for this types of burners requires a different approach. There is a lack of researches, in which will be analyzed changes of the flame length, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. Therefore the aim of this study was to implement and verify the methodology for estimating the flame length, which will allow monitoring changes of operating conditions, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. To carry out the analysis of the image of the coal flame, the two algorithms have been presented. This two algorithms, being based on the video images of the coal flame allows to specify and detect the end point of the flame and on that basis the length of the flame, as well as the fluctuation changes of flame length can be later determined. Both, the change thermal loads of coal burner, streams of secondary air, as well as the constructional change of the angle of swirler assemblies, resulted in distinct changes in the length of the pulverized coal flame.