Fabrication of organic emissive thin films by mist deposition method and evaluation of substrate temperature dependence
Mist deposition method has the advantage of low-cost and energy-saving for the fabrication of organic thin films. We fabricated thin films of organic emissive materials, tris (8-hydroxyquinoline) (Alq3) and rhodamine 6G by the mist deposition method using ultrasonic transducer. The thicknesses of them clearly depend on the substrate temperature during the mist deposition by the boiling point of the solvent. The PL spectra clearly demonstrated that the thin films of Alq3 and rhodamine 6G were successfully fabricated.
Heteroepitaxy of Corundum-Structured α-Ga2O3 Thin Films on α-Al2O3 Substrates by Ultrasonic Mist Chemical Vapor Deposition
Ga2O3 thin films of the α-phase, that is, the corundum structure (in the trigonal system), have been epitaxially obtained on sapphire (α-Al2O3) substrates, in contrast to the strong tendency of Ga2O3 to assume a heterogeneous crystal structure, that is, the β-gallia structure (in the monoclinic system) on sapphire. This result is advantageous for high-quality films and is due to the growth by mist chemical vapor deposition (CVD) at low temperatures of 430–470 °C. The α-Ga2O3 films have narrow full-widths at half maximum (FWHMs) in their X-ray diffraction rocking curves, for example, about 60 arcsec. The root mean square (RMS) roughness of the surface was as small as 1 nm. The optical band gap energy obtained was 5.3 eV, and the films were almost completely transparent in the near-ultraviolet and visible regions. The epitaxial growth of α-Ga2O3 films on sapphire is beneficial for the fabrication of oxide optical and electronic devices.
Morphology and Electrical Properties of Pure and Ti-Doped Gas-Sensitive Ga2O3 Film Prepared by Rheotaxial Growth and Thermal Oxidation
An n-type Ga 2 O 3 semiconductor thin film was prepared by rheotaxial growth and thermal oxidation (RGTO) method on SiO 2 and Al 2 O 3 substrates. Multilayer growth technique was used to control grain size. The morphology and the electrical properties of the Ga and Ga 2 O 3 films were measured as functions of thickness, temperature, and Ti dopant concentration. Measurements of the sensitivity, the response time, and the recovery time of the Ga 2 O 3 films in response to ethanol and CO were carried out. The results showed that the grain size of Ga film increased with thickness, and a balls-on-ball type morphology was produced as the film exceeded 3000 A. Ga 2 O 3 nanowires were created when Ga films were oxidized under impure O 2 atmosphere. Ga 2 O 3 films had an optimum sensing temperature increasing from 625 °C for a 5012 A film to 675 °C for a 5.6-μm film. The films prepared by multilayer growth technique had smaller grain size, but the sensitivity remained unchanged. The films deposited on SiO 2 substrate had a sensitivity higher by 28% than that on Al 2 O 3 . Doping of 0.28 at.% Ti enhanced nanowires growth, raised sensitivity by 6%, shortened response time from 40 to 30 s, but prolonged recovery time from 92 to 130 s. Formation of nanowires resulted in an increase of sensitivity up to 50%. Doping of 2.18 at.% Ti led to the formation of nanoribbons with a sensitivity lower by 8% and a recovery time shortened from 130 to 72 s. The RGTO method was shown to produce Ga 2 O 3 gas-sensitive thin film with good reproducibility.