Papers by Keyword: MOCVD

Abstract: Growth of gallium oxide thin film was realized with MOCVD on (0001) sapphire substrate. Structural and compositional properties of thin film were studied employing trimethylgallium and water as precursors, carrier gases were H₂ and N₂. Obtained film is polycrystalline and predominantly consisted of (201) oriented β-Ga₂O₃. Sample exhibited blue luminescence which is attributed to oxygen vacancies. H₂ gas proved to have beneficial effect on film quality and overall growth process.

Abstract: Copper thin films were deposited on single crystal sapphire substrate via metal-organic MOCVD using Cu (acac)₂ as precursor. X-ray diffraction (XRD) and Scanning Electronic Microscope (SEM) were employed for studying preferred orientation and microstructure. Atomic Force Microscope was utilized in order to characterize roughness of copper thin layer. By calculation of the Gibbs free energy, the reactions have been deeply understood. Depositions were carried out at various substrate temperatures in the rage 473K to 673K. It has been revealed that temperature determined the orientation and microstructure of copper films. At 673K, copper films have exhibited preferred orientation, smooth surface and connected grains, which proved that this copper thin film can act as precursor. Based on the study of epitaxial growth of copper films, a schematic diagram of epitaxial growth relationship is suggested for the step by step depositions processes.

Abstract: An in situ technique for monitoring the growth rate and optical constants of the thin semiconductor layer by the normal-incidence reflectance is proposed. To demonstrate the feasibility of the proposed method, the variation of the air gap between two glasses is used to simulate growth system. We also used the spin coater to thin the thickness of the salad oil to test the performance of the measurement system. The experiments indicate that we can determine the thickness variation and optical constants of the test sample in real time.

Abstract: Utilizing semiconductor nanowires for optoelectronics device requires exact knowledge of their current-voltage properties. In this report, we examine accurate on-top imaging and I-V characterization of individual vertical Gallium Arsenide Nanowires (GaAs NWs) using conductive atomic force microscopy without additional microscopy tools, thus allowing versatile application. The measured current-voltage characteristic of a single NW shows the typical performance of a Schottky contact, which caused by the contact between the metallic AFM tip and the top of NWs. The height of the Schottky barrier is dependent on the diameter of the nanowires. The linear part of the curve was used to calculate the differential resistance, which was found to be about 25 to 100 MΩ. Energy band gap for GaAs NW was found to be 1.5 eV by differential conductivity measurement.

Abstract: In this work the effect of substrate and vaporization temperatures on the structural parameters (sizes of coherent scattering region, values of strain), phase and chemical composition, surface morphology of Co films is revealed. Co films were deposited on Si (100) substrates by Metal-organic chemical vapor deposition using the diiminate complex Co (N’acN’ac)₂ as a precursor. The sizes of coherent scattering region, values of strain and phase composition of Co films were determined by the X-ray diffraction analysis. The chemical composition was identified by the Energy-dispersive X-ray spectroscopy. The surface morphology of Co films was investigated by scanning electron microscope. It is found that the variation of deposition conditions allows us widely to change structural parameters and chemical composition of Co films.

Abstract: To study the effects of Cu/Ba ratio of precursor on YBa₂Cu₃O_7-x (YBCO) film, we have employed the technique of metal-organic chemical vapor deposition to prepare 500 nm thick YBCO films on CeO₂/YSZ/Y₂O₃ (YYC) buffered Ni-W alloy tapes at series of Cu/Ba ratios of precursor. The analysis obtained from X-ray diffraction and scanning electron microscope revealed that the YBCO films crystallized better and became more continuous and denser as Cu/Ba ratio increased from 0.81 to 1.00, yielding that the critical current density (J_c) of YBCO films at 77K and 0T rose from 1.0 MA/cm² to 1.4 MA/cm². Moreover, the energy dispersive spectroscopy indicated that the increase in Cu/Ba ratio of precursor made the Cu/Ba ratio of the YBCO film matrix closer to the theoretical value of 1.5. However, for the Cu/Ba ratio of precursor in the range of 1.00~1.21, the crystallization and texture deteriorated severely and many unexpected precipitates of Ba-Cu-O and Cu-O arose, resulting in the dramatic drop of J_c from 1.4 MA/cm² to 0.1 MA/cm².

Abstract: In the field of packaging, coatings are commonly applied on containers to avoid interactions between them and their content. For glass bottles, application of a thin film prevents interactions with the phase in contact and consequently the alteration of surface properties of the latter. In this article, we propose an innovative way to apply amorphous alumina coatings on glass bottles by metalorganic chemical vapor deposition from aluminum tri-isopropoxide. A numerical model, using the Computational Fluid Dynamics code FLUENT, has been developed to calculate local profiles of gas flow, temperature, concentration and deposition rates into the reactor. The sub-micrometric alumina films have been deposited at reduced pressure between 480°C and 670°C. Uniform thickness profiles have been determined on cross sections over the length of the bottle and have been successfully simulated. Strongly improved hydrolytic resistance with regard to the uncoated bottles reveals the excellent performance of the films.

Abstract: Aluminum 5-fold coordination coexisting with 4-and 6-fold coordination structurally characterizes amorphous aluminum oxide. For nearly 30 years now, ²⁷Al MAS NMR has enabled to detect and later on to quantify this feature thanks to advances in high-resolution instrumentation. The Introduction shortly reviews the results of investigations of 5-coordinate aluminum in amorphous alumina through NMR analysis. Aluminum oxide is not a glass-forming oxide. A convenient way to obtain the amorphous state is by thin film deposition. We present here ²⁷Al NMR analysis of a series of thin films of aluminum oxide prepared by metalorganic chemical vapor deposition (MOCVD) in the temperature range 360 ≤ T_d ≤ 720 °C. In this range, low T_d yield OH-containing films, while high T_d yield nanocrystallites-containing films. The variation of the ^[4]Al, ^[5]Al and ^[6]Al content with T_d is presented and discussed. It is correlated with the T_d dependence of mechanical and corrosion protection properties. These properties are optimal when the structural disorder is to the utmost. Al coordination dependence on film thickness and the formation of metallic aluminum during the deposition process are also presented.

Abstract: BiFeO₃ films undoped and doped with Ba and/or Ti have been fabricated through Metal-Organic Chemical Vapor Deposition (MOCVD) on SrTiO₃ (100), SrTiO₃:Nb (100) and YSZ (100) substrates. Films have been deposited using a multi-metal source, consisting of the Bi (phenyl)₃, Fe (tmhd)₃, Ba (hfa)₂•tetraglyme and Ti (tmhd)₂(O-iPr)₂ (phenyl= -C₆H₅, H-tmhd=2,2,6,6-tetramethyl-3,5-heptandione; O-iPr= iso-propoxide; H-hfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme = CH₃O(CH₂CH₂O)₄CH₃) precursor mixture. The structural and morphological characterization of films has been carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Chemical compositional studies have been performed by energy dispersive X-ray (EDX) analysis. Structural and morphological characterizations point to the formation of crystalline phases and homogeneous surfaces for both undoped and doped BiFeO₃ films. Piezoresponse force microscopy (PFM) and piezoresponce force spectroscopy (PFS) have been applied to study the piezoelectric and ferroelectric properties of the films.

Abstract: Zinc oxide (ZnO) films are deposited on hydrogen (H⁺)-implanted Si and bare Si substrates respectively by Metal-organic Chemical Vapor Deposition (MOCVD). The properties of the films are investigated with Scanning electron microscopy (SEM), X-ray diffraction (XRD), Atom Force Microscopy (AFM), Raman spectra and Photoluminescence (PL) detections, from which we find that compared with bare Si substrate, H⁺-implanted Si can act as a compliant substrate (CS) and effectively improve the crystal quality, decrease the inner stress arisen from the misfit between substrate and epitaxial layer, perfect the film surface smooth degree and optimize the optical quality. At the end, the CS working mechanism is discussed.