Raman Scattering Measurements and Analyses of GaN Thin Films Grown on ZnO Substrates by Metalorganic Chemical Vapor Deposition

Metalorganic chemical vapor deposition (MOCVD) is a popularly used method of growing thin films of GaN on ZnO (GZ) substrates, which pair well due to their structural and characteristic similarities. In this research, optical characterization of the surface quality of GZ sample films is measured by analyzing Raman scattering (RS) using a Renishaw inVia spectrometer fitted with a 532nm laser. Samples were grown in an improved double injection block rotating disc reactor. Multiple samples\u27 spectra show broad peaks that correspond with the E2 (high) and A1 (LO) branches of GaN, and nicely fitted curves are observed for the characteristic E2 (low) and E2 (high) of ZnO. Gaussian fitting of the peaks is used to analyze the spectra data through Origin and Matlab software. The data confirms characteristic peaks for GaN and ZnO that agree with previous spectra of other GZ thin films. Many RS measurements were performed to confirm the crystalline quality of the sample for future characteristic testing

Influence of Al2O3 Passivation Layer Thickness on the Thermal Stability and Quality of MOCVD-Grown GaN on Si

This research delves into the significant impact of varying thicknesses of the Al2O3 passivation layer on the thermal stability and crystalline quality of GaN on Si structures, an essential aspect for the next generation of high-temperature electronic and optoelectronic devices. By adopting metal-organic chemical vapor deposition (MOCVD) for the growth process, we analyzed structures with different Al2O3 passivation layer thicknesses: none, 2 nm, 10 nm, and 20 nm, each built upon the GaN layer. Through Raman spectroscopy, we meticulously assessed the changes in the E2 (High) phonon mode\u27s peak position and full width at half maximum (FWHM) from room temperature up to 300°C. The outcomes highlighted a pronounced relationship between the Al2O3 layer thickness and the GaN on Si structures\u27 thermal behavior and crystalline state. The structure with no Al2O3 layer presented a notable peak shift from 563.23 cm-1 at room temperature to 558.75 cm-1 at 300°C, with FWHM expanding from 9.15 cm-1 to 14.90 cm-1, indicating the least thermal stability. Remarkably, the structure with a 20 nm Al2O3 passivation layer exhibited the highest thermal stability, with the peak position altering minimally from 564.29 cm-1 to 560.15 cm-1 and FWHM increasing from 7.10 cm-1 to 10.76 cm-1 over the same temperature range. This structure stands out as the most favorable for high-temperature operational environments, evidencing that optimal Al2O3 passivation layer thickness can significantly improve GaN on Si devices\u27 thermal stability and crystalline quality. Such findings are vital for designing and developing robust devices capable of enduring extreme thermal conditions, particularly in power electronics and high-frequency transistor applications, where material performance and device reliability are paramount

Advances in Growth, Doping, and Devices and Applications of Zinc Oxide

Zinc oxide is a breakthrough multifunctional material of emerging interest applicable in the areas of electronics, computing, energy harvesting, sensing, optoelectronics, and biomedicine. Zno has a direct and wide bandgap and high exciton binding energy. It is nontoxic, earth-abundant, and biocompatible. However, the growth and characterization of high-quality zno has been a challenge and bottleneck in its development. Efforts have been made to synthesize device-quality zinc oxide and unleash its potential for multiple advanced applications. Zno could be grown as thin films, nanostructures, or bulk, and its properties could be optimized by tuning the growth techniques, conditions, and doping. Zinc oxide could be a suitable material for next generation devices including spintronics, sensors, solar cells, light-emitting diodes, thermoelectrics, etc. It is important and urgent to collate recent advances in this material, which would strategically help in further research and developments in zno. This paper provides a coherent review of developments in zno growth, leading to its advancing applications. Recent developments in growth technologies that address native defects, current challenges in zinc oxide, and its emerging applications are reviewed and discussed in this article

Experimental Demonstration of Inequivalent Mutually Unbiased Bases

Quantum measurements based on mutually unbiased bases (MUB) play crucial roles in foundational studies and quantum information processing. It is known that there exist inequivalent MUB, but little is known about their operational distinctions, not to say experimental demonstration. In this work, by virtue of a simple estimation problem we experimentally demonstrate the operational distinctions between inequivalent triples of MUB in dimension 4 based on high-precision photonic systems. The experimental estimation fidelities coincide well with the theoretical predictions with only 0.16$\%$ average deviation, which is 25 times less than the difference (4.1$\%$) between the maximum estimation fidelity and the minimum estimation fidelity. Our experiments clearly demonstrate that inequivalent MUB have different information extraction capabilities and different merits for quantum information processing

Room temperature deposition of Al-doped ZnO films on quartz substrates by radio-frequency magnetron sputtering and effects of thermal annealing

High-quality Al-doped zinc oxide (AZO) thin films have been deposited on quartz substrates by radio-frequency magnetron sputtering at room temperature for thin film solar cell applications as transparent conductive oxide (TCO) electrode layers. Effects of post-deposition annealing treatment in pure nitrogen and nitrogen/hydrogen atmosphere have been investigated. Annealing treatments were carried out from 300 degrees C to 600 degrees C for compatibility with typical optoelectronic device fabrication processes. A series of characterization techniques, including X-ray diffraction, scanning electron microscopy, Hall, optical transmission, and X-ray photoelectron spectroscopy has been employed to study these AZO materials. It was found that there were significant changes in crystallinity of the films, resistivity increased from 4.60 x 10(-4) to 4.66 x 10(-3) Omega cm and carrier concentration decreased from 8.68 x 10(20) to 2.77 x 10(20) cm(-3) when annealing in 400 degrees C pure nitrogen. Whereas there were no significant changes in electrical and optical properties of the AZO films when annealing in 300-500 degrees C nitrogen/ hydrogen atmosphere, the electrical stability of the AZO films during the hydrogen treatment is attributed to both desorption of adsorbed oxygen from the grain boundaries and production of additional oxygen vacancies that act as donor centers in the films by removal of oxygen from the ZnO matrix. These results demonstrated that the AZO films are stably suited for TCO electrodes in display devices and solar cells. (C) 2010 Elsevier B.V. All rights reserved