Mist Chemical Vapor Deposition Research Articles

Ultrasonic‐assisted mist chemical vapor deposition of II‐oxide and related oxide compounds

AbstractBasic concepts of ultrasonic‐assisted mist chemical vapor deposition (CVD), and its applications to the fabrication of II‐oxide and related oxide films are described. Fairly good thin film properties and device performance, compared to those achieved by conventional vacuum‐based processes, encourage the mist CVD as a simple, inexpensive, energy‐saving and non‐vacuum process, opening new and wide application of oxide materials for novel devices supporting the future environment. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication and characterization of Cu2O, ZnO and ITO thin films toward oxide thin film solar cell by mist chemical vapor deposition method

AbstractN‐type zinc oxide (ZnO) and p‐type cuprous oxide (Cu2O) thin films were fabricated by an ultrasonic spray‐assisted mist chemical vapor deposition (mist CVD) method. The films of transparent conductive gallium‐doped ZnO (ZnO:Ga) and indium tin oxide (ITO) were also formed by the same technique. ZnO thin films have showed n‐type conductivity with carrier concentration of 3.6 × 1019 cm–3 and mobility of 8.6 cm2/V·s. Cu2O thin films showed p‐type conductivity whose carrier density and mobility were 3.3 × 1015 cm–3 and 0.20 cm2/V·s, respectively. ZnO:Ga and ITO thin films have high transmittance over 85% in visible region and low resistivity values of 2.3 × 10–3 and 1.4 × 10–4 Ω·cm, respectively. These properties are suitable for transparent electrodes of solar cells. The results encourage the successive fabrication by the same process technique of solar cell structure, that is, the multilayer structure of ITO (or conductive ZnO), n‐ZnO, and p‐Cu2O films on a glass substrate. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced mobility of Li-doped ZnO thin film transistors fabricated by mist chemical vapor deposition

Mist chemical vapor deposition (mist-CVD)-processed, lithium (Li)-doped ZnO thin film transistors (TFTs) are investigated. Li doping significantly increases the field-effect mobility in TFTs up to ∼100 times greater than that of undoped ZnO. The addition of Li into mist-CVD-grown ZnO semiconductors leads to improved film quality, which results from the enhanced crystallinity and reduced defect states, including oxygen vacancies. Our results suggest that Li doping of ZnO-based oxide semiconductors could serve as an effective strategy for high-performance, mist-CVD-processed oxide TFTs with low-cost and low-temperature fabrication.

Mist chemical vapor deposition of aluminum oxide thin films for rear surface passivation of crystalline silicon solar cells

We show the promising potential of mist chemical vapor deposition (CVD), a nonvacuum and solution-based technology, for the growth of an AlOx film as a rear surface passivation layer of crystalline silicon (c-Si) solar cells, supported by its safety, low process cost, and low energy consumption for the growth. The AlOx layer grown at 350 °C with aluminum acetylacetonate and ozone, without a successive annealing process, showed an excellent surface passivation property with the negative fixed charge density of about (1–2) × 1012 cm−2, as highlighted by the surface recombination velocity of ∼10 cm/s.

Fabrication of Zinc Oxide Nanostructures by Mist Chemical Vapor Deposition

Fabrication of Zinc Oxide Nanostructures by Mist Chemical Vapor Deposition

Mist chemical vapor deposition for thin-film deposition at atmospheric pressure to move toward a green process for oxide-based electronics

Mist chemical vapor deposition for thin-film deposition at atmospheric pressure to move toward a green process for oxide-based electronics

Oriented growth of beta gallium oxide thin films on yttrium‐stabilized zirconia substrates

Abstract(‐201)‐oriented beta gallium oxide (β‐Ga2O3) thin films were grown on yttrium‐stabilized zirconia (YSZ) substrates using a mist chemical vapor deposition (CVD) method. The lowest full‐width at half maximum value in ω‐scan X‐ray diffraction was 0.50°, obtained for the growth temperature of 650 °C on a YSZ(100) substrate. Observation by a secondary electron microscope (SEM) revealed flat surface including large‐scale precipitates. Electron diffraction patterns suggested that thin films basically possess β‐type crystal structure though crystal precipitates were formed by poly‐crystal. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal stability of single crystalline alpha gallium oxide films on sapphire substrates

AbstractHigh quality single crystalline alpha gallium oxide (α‐Ga2O3) films, as highlighted by the X‐ray diffraction ω‐scan full‐width at half maximum of as small as 30 arcsec, were prepared by the mist chemical vapor deposition (CVD). The quality of the film was markedly dependent of the carrier gas flow rate, so we need careful attention for the optimum growth conditions. The thermal stability of α‐Ga2O3 films was investigated by studying their thermal stability under thermal annealing in terms of the structural and optical properties. It was found that α‐Ga2O3films grown at 470 °C are stable until 550 °C, but are gradually transformed to β‐Ga2O3over 600 °C. Finally, β‐Ga2O3films only existed at 700 °C. So the device processes for α‐Ga2O3 should be done below 550 °C to avoid phase transformation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Epitaxial growth of wide-band-gap ZnGa2O4 films by mist chemical vapor deposition

ZnGa2O4 films were grown on (100) MgAl2O4 substrates by mist chemical vapor deposition. A growth window for obtaining single spinel phase was revealed by systematic variations of precursor Zn/Ga ratio and growth temperature, where the cation stoichiometry was maintained through sublimation of excess Zn species before crystalized into ZnO. The epitaxial relationship to the substrate was identified to be cube on cube with no rotation domain. The optical properties of the fully relaxed film were characterized by using cathodoluminescence (CL) and absorption spectroscopies. A large Stokes shift was found between the CL peak energy (3.4eV) and fundamental absorption edge (4.6eV), reflecting typical property of Ga-based wide-band-gap oxide semiconductors.

19.3: Morphology Controlled Single‐crystal ZnO Nanostructures Fabricated by a Novel Mist Chemical Vapor Deposition

AbstractA novel method is developed to synthesize single crystal ZnO nanostructures combining the reducing thermal annealing and mist chemical vapor deposition processes. The sizes of ZnO single crystal structures can be controlled with adjusting the parameters in mist CVD. The structural and optical properties of ZnO nanostructures are investigated.

Growth and electrical properties of AlOx grown by mist chemical vapor deposition

Aluminum oxide (AlOx) thin films were grown using aluminum acetylacetonate (Al(acac)3) as a source solute by mist chemical vapor deposition (mist CVD). The AlOx thin films grown at temperatures above 400°C exhibited a breakdown field (EBD) over 6 MV/cm and a dielectric constant (κ) over 6. It is suggested that residual OH bonding in the AlOx thin films grown at temperatures below 375°C caused degradation of the breakdown field (EBD). With FC type mist CVD, the reaction proceeded efficiently (Ea = 22–24 kJ/mol) because the solvent, especially H2O, worked as a stronger oxygen source. The AlOx film could be grown at 450°C with a high deposition rate (23 nm/min) and smooth surface (RMS = 1.5 nm). Moreover, the AlOx thin films grown by mist CVD had excellent practicality as insulators because the gate leakage current (IG) of the oxide thin film transistor (TFT) with an IGZO/AlOx stack was suppressed below 1 pA at a gate voltage (VG) of 20 V.

Effect of O3 and Aqueous Ammonia on Crystallization of MgO Thin Film Grown by Mist Chemical Vapor Deposition

Mist chemical vapor deposition (CVD) has been applied to fabricate MgO thin films under atmospheric pressure. In this work, to fabricate highly crystalline MgO thin films at low temperature, the effects of ozone gas (O3), aqueous ammonia (NH3), and a combination of O3 and NH3 on the crystallization temperature were studied by comparing samples grown under a standard condition of inactive gas such as argon (Ar). It was clarified that the crystallization temperature was decreased from 450 to 400 °C by the assistance of O3 and the crystallinity was improved by the addition of NH3. The growth of higher crystallinity MgO thin films at temperatures above 400 °C was possible by the combination of O3 and NH3, which caused stronger enhancement of the crystallization temperature and crystallinity. The causes of these effects were analyzed thermodynamically, and it was clarified that the results were due to the activated oxygen sources and the stability level of precursor materials in the solution.

Plasma-Assisted Mist Chemical Vapor Deposition of Zinc Oxide Films Using Solution of Zinc Acetate

Zinc oxide (ZnO) film deposition has been carried out by plasma-assisted mist chemical vapor deposition (CVD) using a solution of zinc acetate [Zn(CH3COO)2], and the effects of plasma exposure on film properties have been investigated in terms of RF power. With increasing RF power, the results of the X-ray diffraction (XRD) patterns of ZnO films with plasma exposure showed the existence of crystallized ZnO films with plasma exposure. Under this condition, the substrate temperature was as low as 200 °C for a plasma exposure time of 20 min. The surface morphology shown by scanning electron microscopy (SEM) images shows that the ZnO films were textured with round grains, which is attributed to the effect of the use of mist with the precursor.

Crystal Structure of Non-Doped and Sn-Doped α-(GaFe)2O3Thin Films.

ABSTRACTCorundum structured α-(GaFe)2O3alloy thin films were obtained on c-plane sapphire substrates by the mist chemical vapor deposition method. Wide range of X-ray diffraction 2θ/θ scanning measurements indicated that these crystals were epitaxially grown on c-plane sapphire substrates and these are no other crystal oriented phase. The cross-sectional and plane-view transmission electron microscope images showed the growth along the c-axis of α-(GaFe)2O3thin films on sapphire substrates, forming joint of columnar structure. The non-doped α-(GaFe)2O3thin films showed ferromagnetic properties at 300 K, though the origin of ferromagnetism still remained unresolved. In order to enhance the spin-carrier interaction, Sn doped α-(GaFe)2O3alloy thin films were fabricated on c-plane sapphire substrates. X-ray diffraction 2θ/θ and ω scanning measurement results indicated that the highly-crystalline films were epitaxially grown on substrates in spite of the Sn-doping.

Growth and Band Gap Control of Corundum-Structured α-(AlGa)2O3Thin Films on Sapphire by Spray-Assisted Mist Chemical Vapor Deposition

Growth and Band Gap Control of Corundum-Structured α-(AlGa)₂O₃Thin Films on Sapphire by Spray-Assisted Mist Chemical Vapor Deposition

Growth and Band Gap Control of Corundum-Structured α-(AlGa)2O3 Thin Films on Sapphire by Spray-Assisted Mist Chemical Vapor Deposition

Following the previous achievement of highly crystalline α-Ga2O3 thin films on c-plane sapphire, the growth of corundum-structured α-(AlxGa1-x)2O3 was examined aiming at the future application of α-(AlxGa1-x)2O3/Ga2O3 heterostructures to power devices and other functional devices. The results show the control of x and band gap up to 0.81 and 7.8 eV, respectively, maintaining the dominant corundum structure. The transmission electron microscope observation suggested the formation of the crystallographically good interface of α-(AlxGa1-x)2O3/Ga2O3 without the severe generation of threading dislocation lines from the interface.

Fabrication of Silicon Oxide Thin Films by Mist Chemical Vapor Deposition Method from Polysilazane and Ozone as Sources

Fabrication of Silicon Oxide Thin Films by Mist Chemical Vapor Deposition Method from Polysilazane and Ozone as Sources

Epitaxial growth of γ-Ga2O3 films by mist chemical vapor deposition

Undoped Ga2O3 thin films were synthesized from an aqueous solution by using mist chemical vapor deposition. The defective-spinel-type γ-phase and corundum-type α-phase were epitaxially stabilized when deposited on (100) MgAl2O4 and (0001) sapphire substrates, respectively. The epitaxial relationship for the γ-phase film was identified to be cube on cube. We found that these metastable phases were obtained at lower growth temperatures, which gradually transformed to the stable β-phase with increasing temperatures. The temperature dependence of growth rate on the MgAl2O4 exhibited a clear transition from surface-reaction-limited to diffusion-limited regime and a growth window for the γ-phase was found in the vicinity of the transition. For a pure γ-phase film, refractive index in a visible region, direct and indirect band-gaps were estimated to be 2.0∼2.1, 5.0 and 4.4eV, respectively, at room temperature.

Fabrication of Silicon Oxide Thin Films by Mist Chemical Vapor Deposition Method from Polysilazane and Ozone as Sources

Silicon oxide thin films were grown from the liquid source, polysilazane, by using mist chemical vapor deposition (CVD) at temperatures of 200–350 °C. The films were grown with a reasonable growth rate of 12 nm/min at the temperature of 200 °C, and they showed resistivity of the order of 1013 Ω·cm, although the incorporation of carbon and oxygen remains as a problem to be discussed and solved in the future. The results are encouraging for the future application of mist CVD for the growth of silicon oxide films on plastic substrates.

Characterization of inductively coupled RF plasmas for plasma-assisted mist CVD of ZnO films

A plasma-assisted mist chemical vapor deposition (CVD) system with a high-density inductivity coupled RF plasma (ICP) source has been developed for low-temperature and high-rate deposition of zinc oxide films. In this paper, characterization of an ICP for plasma-assisted mist CVD is reported. It was found that the plasma density measured with a cylindrical Langmuir probe was as high as 1.2 × 1011 cm−3 and the electron temperature was 1.0 − 2.5 eV for an Ar plasma. The gas temperature in the ICP determined from molecular optical emission spectroscopy was 1450 K at an RF power of 1000 W for an Ar/air plasma. These results demonstrate that a plasma sustained by an inductively coupled RF plasma source has sufficient enthalpy for vaporization of mists and also has a high density for efficient dissociation of precursors and generation of oxygen radials during ZnO film deposition using plasma-assisted mist CVD.