We determine the band alignment of ScxAl1-xN/GaN heterojunctions at ScN alloy fractions ranging from x = 0.04 to 0.20 using x-ray photoemission spectroscopy, and determine the band gap from spectroscopic ellipsometry. We find a transition from straddling to staggered gap as ScN alloy fraction increases, and show that the experimental results are consistent with first-principles calculations. This crossover from type-I to type-II band alignment shows a degree of freedom for engineering improved heterostructures in ScAlN/GaN-based electronic and optoelectronic devices.
Spectroscopic ellipsometry is commonly used for the optical characterization of solid state thin films and bulk substrates. In recent years, it has also gained widespread use in characterizing organic films . The discovery of carbon nano-tubes has increased the utility of organic films by allowing the engineer to alter the electrical and mechanical properties of the material by doping the film with these graphite structures. Proper understanding through PMSE characterization of the structure is necessary to control desired optical and electrical properties. In this work we present mothodes of PMSE as an advantageous, non-destructive optical tool for the study of C70 doped PS-PHMA thin film on a c-Si(100) wafer. For the samples measured, concentration of C70 is reported along with dispersion relations for PS-PHMA films in the UV-Vis spectrum for untreated, heated and shear aligned films. There is also evidence that the C70 may also align within the micro-domain of the PS-PHMA producing an anisotropic film.
Due to they can be tailored to provide a wide range of physical properties and their easiness of processing and fabrication, polymeric materials have found widespread use in the manufacture of microwave, electronics, photonics and bio-tech systems. This paper presents the basic principle of phase modulation spectroscopic ellipsometer (PMSE) and its advantages over other ellipsometry in measuring polymer film. Used for thin film measurements ultra-thin dielectric, meal film and organic film, the PMSE technique is now used over a wide spectral range from the vacuum ultraviolet to the mid infrared. Film thickness ranging from Angstrom up to 50um can be measured by PMSE. Applications of PMSE on measurement and characterization of polymer/organic material are given in the paper.
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