Vacuum Metalorganic Chemical Vapor Deposition Research Articles

Structural and optical properties of heteroepitaxial anatase titania films on MgAl6O10 (100) substrates by MOCVD

Titania (TiO2) films were synthesized on MgAl6O10 (100) substrates by high vacuum metalorganic chemical vapor deposition (MOCVD). The crystal structures, surface and interface morphologies as well as the optical properties of the obtained TiO2 films depending on substrate temperature were studied in detail. A single-crystal anatase TiO2 (a-TiO2) film was obtained at the substrate temperature of 550°C. The epitaxial relationship between the a-TiO2 film and MgAl6O10 (100) substrate was a-TiO2 (001) || MgAl6O10 (100) with a-TiO2 [100] || MgAl6O10 [001]. The a-TiO2 film showed an average transmittance of 95.1% in the visible range, and an optical band gap of 3.46eV. The refractive indexes and extinction coefficients of the obtained TiO2 films as a function of wavelength were analyzed. A broad photoluminescence peak centered at 535nm was observed at room temperature and the corresponding luminescence mechanisms were discussed.

Preparation and characterization of transparent indium- doped TiO 2 films deposited by MOCVD

Abstract Titanium dioxide (TiO 2 ) films doped with different indium (In) concentrations have been prepared on SrTiO 3 (STO) substrates by high vacuum metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) analyses revealed the TiO 2 films doped with low In concentrations to be [001] oriented anatase phase and the films with high In concentrations to present polycrystalline structures. The 1.8% In-doped TiO 2 film exhibited the best electrical conductivity properties with the lowest resistivity of 8.68×10 −2 Ω cm, a Hall mobility of 10.9 cm 2 V −1 s −1 and a carrier concentration of 6.5×10 18 cm −3 . The films showed excellent transparency with average transmittances of over 85% in the visible range.

Cubic SiC Nano-Thin Films and Nano-Wires: High Vacuum Metal-Organic Chemical Vapor Deposition, Surface Characterization, and Application Tests

Single-crystalline and epitaxial cubic silicon carbide (beta-SiC) nano-thin films have been deposited on Si(100) substrates at a sample temperature of approximately 900 degrees C using single source precursors by the thermal metal-organic chemical vapor deposition (MOCVD) method. Diethylmethylsilane and 1,3-disilabutane, which contain Si and C atoms in the same molecule, were used as precursors without any carrier or bubbler gas. Upon increasing the deposition temperature from 900 to 950 degrees C, beta-SiC nano-thin films with relatively small crystals and smoother surfaces were created on Si(100) substrates. Moreover, beta-SiC nano-wires with 40 approximately 100 nm in diameter have also been grown selectively on nickel catalyzed Si(100) substrates with dichloromethylvinylsilane by the MOCVD method. The deposition temperature in this case was as low as 800 degrees C under the pressure of 5.0 x 10(-2) Torr. It is worth noting that the initial growth rates of deposited beta-SiC nano-thin films and nano-wires strongly depend on the deposition temperature rather than the time. In order to test the possibility of applications of these materials for electronic components such as field emitter, MEMS, and high-power transistor, we fabricated the nanoelectronic devices using both beta-SiC nano-wires and nano-thin films. With these preliminary application tests, it is expected that SiC nanowires can be used as field emitter and nanoelectronic high-power transistor, and application of the SiC nano-thin films to MEMS is promising as well.

Growth of single crystalline GaN thin films on Si(111) substrates by high vacuum metalorganic chemical vapor deposition using a single molecular precursor

Hexagonal GaN thin films were grown on Si(111) substrates using single molecular precursor by high vacuum metalorganic chemical vapor deposition at various temperatures from 600 to 800 °C and pressures in the range of 2×10−6 to 2×10−5 Torr. We first developed and synthesized the single molecular precursor of diethylazidogallium methylhydrazine adduct, [(Et)2Ga(N3)HzMe], with the objectives of reducing carbon content in the GaN films and lowering growth temperatures. Results of x-ray diffraction (XRD), x-ray pole figure, and x-ray photoelectron spectroscopy measurements showed that this approach yielded a single crystalline GaN thin film of [0002] orientation with relatively low carbon content. Ga-rich compositions Ga:N of 1:0.92 were obtained at a temperature of 750 °C and a pressure of 2×10−6 Torr. However, for growth temperatures below 700 °C, we found the films to be polycrystalline. Scanning electron microscope (SEM) and atomic force microscope (AFM) images showed that the as-grown GaN films have a smooth surface morphology. Based on XRD, AFM, and SEM results, we identified effects of deposition temperature and pressure on the growth rate and crystallinity, and can suggest that our deposition process is governed by diffusion rate control. Optical properties were investigated by photoluminescence, which revealed an emission peak at 3.40 eV with a full width at half-maximum of approximately 100 meV for a GaN film grown at 750 °C and 2×10−6 Torr.

Deposition of silicon carbide films using a high vacuum metalorganic chemical vapor deposition method with a single source precursor: Study of their structural properties

Silicon carbide (SiC) thin films were prepared on Si(100) substrates by high vacuum metalorganic chemical vapor deposition using a single-source precursor at various growth temperatures in the range of 700–1000 °C. The precursor is diethylmethylsilane, and is used without carrier gas. The effects of substrate temperature as well as deposition time on the crystal growth were investigated. The optimum temperature for the formation of high quality polycrystalline SiC thin films was found to be 900 °C on the basis of x-ray diffraction and transmission electron diffraction results. X-ray photoemission spectroscopy shows that SiC films grown at 900 °C have slightly carbon-rich compositions (Si:C=1:1.2) in the surface region, but stoichiometric composition in the bulk. Scanning and transmission electron microscope images show the influence of substrate temperature on the grain size and crystallinity of the films. Large grain sizes and high quality crystallinity can be obtained below 900 °C.

Deposition of epitaxial silicon carbide films using high vacuum MOCVD method for MEMS applications

Silicon carbide (SiC) thin film have been prepared on both Si(100) and SiO 2 patterned Si(100) substrates by the high vacuum metal-organic chemical vapor deposition (MOCVD) method using a single source precursor at various growth temperatures in the range of 700–1000 °C. Diethylmethylsilane(DEMS) was used as precursor without carrier gas. The effects of substrate temperature as well as deposition time on the crystal growth and hardness were mainly investigated in this study. The optimum temperature for the formation of the epitaxial SiC thin films were found to 900 °C on the basis of XRD results. However, the XPS result shows that the SiC film grown at 900 °C have carbon rich (Si:C=1:1.2 composition) surface due to surface reaction of the precursor itself. From the SEM images, substrate temperature has influence on the grain size and crystallinity of the SiC films. Especially, the major crystal form of these deposited films was rectangular in shape on the substrates at 900 °C. We also obtain a high hardness SiC thin film with 32 GPa.

High vacuum chemical vapor deposition of cubic SiC thin films on Si(001) substrates using single source precursor

Thin films of cubic SiC have been prepared on Si(001) substrates in situ by high vacuum metal-organic chemical vapor deposition (HVMO-CVD) method using a single source precursor at various growth temperatures in the range of 300–1000°C. 1,3-Disilabutane, H 3Si-CH 2-SiH 2-CH 3 (DSB) that contains the same amount of silicon and carbon atoms in the same molecule was used as precursor without carrier gas. During HVMO-CVD, moreover, a series of as-deposited SiC/Si(001) thin films were simultaneously characterized by in situ X-ray photoelectron spectrometry (XPS) under the UHV condition without air exposure. XPS and Rutherford backscattering spectroscopy (RBS) show that the SiC films grown at above 700°C have stoichiometric composition. However, the films grown at below 700°C show Si-rich stoichiometry. Transmission electron microscopy (TEM) confirms the crystalline nature of the SiC films. The optimum temperatures for the formation of the epitaxial 3C–SiC thin films were found to be between 900 and 1000°C on the basis of XRD and TED analysis. In this study, the best film with maximum growth rate of 0.1 μm/h was obtained from a SiC film grown at 900°C and 8.7×10 −4 Pa of DSB. The SiC/Si interface is clearly shown in secondary ion mass spectroscopy (SIMS) depth profile as judged by the sharp decrease 13C signals. The thickness of the as-grown films was determined using cross-sectional scanning electron microscopy (SEM) and RBS, and two different activation energies for 3C–SiC formation were obtained from the Arrhenius plots.

Improvement of Gaas Crystal Quality on Si Grown by Mocvd Through Two-Dimensional-Like Nucleation with Low Temperature in Situ Hydrogen/Arsine Plasma Cleaning

ABSTRACTWe report the significant improvement of GaAs crystal quality on Si grown by metal-organic chemical vapor deposition (MOCVD) with an in situ low temperature hydrogen/arsine plasma cleaning of the Si substrate at 450°C and a consequent controlled two-dimensional-like morphology of the low temperature buffer layer at its early stage. The most critical step that determines the interfacial cleanliness and the early stages of the nucleation and thin film formation of heteroepitaxial GaAs on Si in a non-ultrahigh vacuum MOCVD system is the substitution of hydrogen atoms passivating the Si surface after ex situ HF-dip with pas-sivating As atoms. Reduction of in situ cleaning temperature ensures the very slow kinetics of thermal desorption of the hydrogen atoms and re-oxidation of exposed Si surface from the reactor environment, and provides a fully As-passivated Si surface, leading to a 2D-like buffer layer.

A new low temperature III–V multilayer growth technique: Vacuum metalorganic chemical vapor deposition

A new technique for multilayer growth by metalorganic chemical vapor deposition is described. The vacuum metalorganic chemical vapor deposition technique combines the low-temperature growth capability of molecular beam epitaxy with the source handling system of chemical vapor deposition. The viability of the new technique is demonstrated by the growth of high-mobility layers of GaAs, GaAs(1−x)P(x), and Ga(1−x)In(x)As at 570 °C. Room-temperature mobilities of GaAs films as high as 4990 cm2/V s are obtained. Doping of both p-type and n-type films is demonstrated. GaAs shallow homojunction solar cells fabricated with this technique are described. Active-area solar cell efficiencies as high as 19.6% are obtained with 6 ’’suns’’ AM2 concentrated light. This multilayer growth technique is particularly suited to the fabrication of multicolor solar cells.