Metalorganic Chemical Vapor Deposition Method Research Articles

Improved Electrical Characteristics of Amorphous Oxide TFTs Based on $\hbox{TiO}_{x}$ Channel Layer Grown by Low-Temperature MOCVD

We report on the fabrication of n-type thin-film transistors (TFTs) based on TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> channels grown by the metal-organic chemical vapor deposition method with the chamber temperature of 250degC. These TFTs exhibit ideal characteristics with the flat saturation, low subthreshold swing, and narrow hysteresis window, all of which are a clear improvement from our previous work based on TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles. The TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> film in this letter is identified to be in the amorphous phase from X-ray diffraction analysis, and its carrier density is estimated to be 2.6 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> from the transmission line model and analysis of TFT on-resistance measured at various gate biases and channel lengths.

Controllable Growth and Characterization of ZnO/MgO Quasi Core−Shell Quantum Dots

ZnO/MgO quasi core−shell quantum dots (QDs) were grown by a metal-organic chemical vapor deposition method on silicon substrates. The core−shell structure was well-characterized by a combination of cross-sectional transmission electron microscopy and angle-resolved X-ray photoelectron spectroscopy (XPS). Valence band XPS measurements were performed to investigate the effects of MgO shell layer on the energy band of ZnO/MgO QDs. Photoluminescence (PL) emission from the QDs showed remarkable enhancement after the growth of the MgO layer. In addition, exciton binding energy of 118 ± 5 meV in the ZnO/MgO QDs was obtained from temperature-dependent PL.

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.

Plasma-free nitrogen doping and homojunction light-emitting diodes based on ZnO

The authors develop a plasma-free metalorganic chemical vapour deposition method to grow N-doped p-type ZnO films. The incorporation of the N acceptor and the corresponding change in the Fermi level are well confirmed by x-ray photoelectron spectroscopy. Temperature-dependent photoluminescence reveals the acceptor-related emissions, namely, neutral acceptor-bound exciton and probably donor–acceptor pair transition. In addition, typical rectifying I–V characteristics and room-temperature electroluminescence from ZnO homojunction light-emitting diodes are demonstrated.

Structural and photoluminescence properties of single-crystalline In 2O 3 films grown by metal organic vapor deposition

Single-crystalline In 2O 3 thin films were obtained on α-Al 2O 3 (0 0 0 1) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The structural, optical and photoluminescence (PL) properties of the In 2O 3 films were investigated in detail. The sample prepared at 650 °C exhibited best crystal quality with body-centered cubic (bcc) structure of pure In 2O 3. The average transmittance for the films in the visible spectral range exceeded 85%. A single and sharp ultra-violet PL peak near 337 nm was observed at room temperature (RT). The corresponding PL mechanisms were investigated.

Study on plasma assisted metal-organic chemical vapor deposition of Zr(C,N) and Ti(C,N) thin films and in situ plasma diagnostics with optical emission spectroscopy

Zr(C,N) and Ti(C,N) films were synthesized by pulsed dc plasma assisted metal-organic chemical vapor deposition method using metal-organic compounds of tetrakis diethylamido titanium and tetrakis diethylamido zirconium at 200–300°C. To change the plasma characteristics, different carrier gases such as H2 and He∕H2 were used and, as the reactive gas, N2 and NH3 were added to the gas mixture. The effect of N2 and NH3 gases was also evaluated in the reduction of C content of the films. Radical formation and ionization behaviors in plasma were analyzed by optical emission spectroscopy and mass spectrometry at various pulsed biases and gas conditions. The gas mixture of He and H2 as the carrier gas was very effective in enhancing the dissociation of molecular gases. In the case of N2 addition, N2 as reactive gas resulted in higher hardness. However, NH3 as reactive gas highly reduced the formation of CN radical, thereby greatly decreasing the C content of Zr(C,N) and Ti(C,N) films. The hardness of the film is 1400–1700HK depending on gas species and bias voltage. Higher hardness can be obtained for a H2 and N2 gas atmosphere and bias voltage of −600V. Plasma surface cleaning using N2 gas prior to deposition appeared to increase the adhesion of films on steel. The changes of plasmas including radicals and film properties are illustrated in terms of carrier and reactive gases, as well as pulsed power variation.

Self-Catalytic and Selective Growth of ZnO Nanoneedles by Micro-Contact Printing and CVD

A self-catalytic method to selectively grow ZnO nanoneedles is demonstrated by simply combining a conventional micro-contact printing (mu-CP) and two-step metal-organic chemical vapor deposition (MOCVD) techniques. Self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) were patterned on Si substrates by mu-CP. The patterned structures of the ZnO nanoneedles were realized on the SAMs-patterned Si substrates by two-step MOCVD at high temperature of 600 degrees C via the initial preparation of a thin ZnO seed layer with retaining the patterned morphology at low temperature of 170 degrees C. This combined method of mu-CP and self-catalytic two-step MOCVD should be applicable to fabricate the patterned alignments of metal oxide nanostructures.

Preparation of CuGaS 2 thin films by two-stage MOCVD method

Copper gallium disulfide (CuGaS 2; CGS) films were deposited on glass or ITO glass by two-stage metal-organic chemical vapor deposition (MOCVD) method, using Cu- and Ga/S-containing precursors without toxic H 2S gas. First, pure Cu thin films were prepared on glass substrates by using a single-source precursor, bis(ethylbutyrylacetato)copper(II) or bis(ethylisobutyrylacetato)copper(II). Second, the resulting Cu films were processed using tris( N, N-ethylbutyldithiocarbamato)gallium(III) at 410–470 °C to produce CuGaS 2 films. The optical band gap of the CGS film grown at 440 °C was about 2.53 eV. In addition, it was found that the elemental ratio of Cu and Ga elements of the CGS films can be elaborately adjusted by controlling deposition conditions on demand.

Transport Characteristics of CVD-YBCO Coated Conductor under Hoop Stress

Transport characteristics of IBAD/ CVD-YBa2Cu3O7 (YBCO) coated conductor were measured at 4.2 K under hoop stress. The conductor was fabricated by a multi-stage metal-organic chemical vapor deposition (CVD) method. The YBCO layer was deposited on Hastelloy substrate with PLD-Ce02 and IBAD-Gd2Zr207 buffer layers. A 20-mum silver layer was sputtered as a protective and stabilizing layer. The hoop stress test coils were fabricated by winding the conductor on a 250-mm diameter stainless-steel bobbin by five turns. Two coils, denoted as coils A and B, were fabricated. The Hastelloy substrate located outside for coil A and inside for coil B. Both coils were tested in magnetic field at 4.2 K under hoop stresses. Coil A and B experienced 1028 and 777 MPa at 11 T, 4.2 K. The measured stress-strain curves provided that the Young's modulus of the conductor was 190 GPa. The tolerable stress of ~1000 MPa and the Young's modulus of 190 GPa are consistent with the values obtained by a tensile test. The hoop stress test results indicates that the YBCO coated conductor is promising for application under huge hoop stress.

Structural and photoluminescence properties of single crystalline SnO 2:In films deposited on α-Al 2O 3 (0 0 0 1) by MOCVD

Indium-doped tin oxide (SnO 2:In) films have been prepared on α-Al 2O 3 (0 0 0 1) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The structural and photoluminescence (PL) properties of the SnO 2:In films were investigated. The prepared samples were epitaxial single crystalline films having rutile structure of pure SnO 2 with the best single crystalline structure obtained at 4% (atomic ratio) of In concentration. A single ultra-violet (UV) PL peak near 339 nm was observed at room temperature (RT) for the 4% In-doped film. At a temperature of 14 K, another narrow PL peak located at 369 nm and a broad feeble peak near 493 nm were also observed. The corresponding PL mechanisms were investigated.

Rapid thermal annealing induced changes on the contact of Ni/Au to N-doped ZnO

N-doped p-type ZnO (p ∼ 10 18cm -3) was grown on sapphire(0 0 0 1) substrate by metal-organic chemical vapor deposition method. Ni/Au metal was evaporated on the ZnO film to form contacts. As-deposited contacts were rectifying while ohmic behavior was achieved after thermally annealing the contacts in nitrogen environment. Specific contact resistance was determined by circular transmission line method and a minimum specific contact resistance of 8 × 10 −4 Ω cm 2 was obtained for the sample annealed at 650 °C for 30 s. However, Hall effect measurements indicate that, as the rapid thermal annealing temperature increased up to 550 °C or higher the samples’ conductive type have changed from p-type to n-type, which may be due to the instability nature of the present-day p-type N-doped ZnO or the dissociation of ZnO caused by annealing process in N 2 ambient. Evolution of the sample's electric characteristics and the increment of metal/semiconductor interface states induced by rapid thermal annealing process are supposed to be responsible for the improvement of electrical properties of Au/Ni/ZnO.

Thickness determination of SrZrO 3 thin films using both X-ray reflectometry and SIMS techniques

High- k SrZrO 3 perovskite thin films, suitable for microelectronics applications were deposited under various conditions on plane Si (100) substrates by direct liquid injection metal-organic chemical vapor deposition (MOCVD) method. Depending on the deposition temperature, films were mono- or multi-layered and either crystallized either amorphous. Amorphous films were annealed in order to obtain the expected orthorhombic perovskite structure. The thicknesses of individual layer as well as multi-layers of the stacks were determined with reflectometry measurements. SIMS measurements were also conducted on the thin films to estimate the order of the multi-layers. Thicknesses were successfully confirmed by this destructive method and chemical environment of the films was determined as well as the composition of the layers. Compared with infrared transmission measurements on as-deposited and post-annealed films, it gives clues on desorption of volatile species. Thus, crystallographic and chemical structures were precise on studied samples.

Optical and Magnetic Properties of Fe-Doped GaN Diluted Magnetic Semiconductors Prepared by MOCVD Method

Fe-doped GaN thin films are grown on c-sapphires by metal organic chemical vapour deposition method (MOCVD). Crystalline quality and phase purity are characterized by x-ray diffraction and Raman scattering measurements. There are no detectable second phases formed during growth and no significant degradation in crystalline quality as Fe ions are doped. Fe-related optical transitions are observed in photoluminescence spectra. Magnetic measurements reveal that the films show room-temperature ferromagnetic behaviour. The ferromagnetism may originate from carrier-mediated Fe-doped GaN diluted magnetic semiconductors or nanoscale iron clusters and Fe-N compounds which we have not detected.

Study of selective deposition of TaN thin films on OTS patterned Si(100) substrates

Cubic TaN thin films have been selectively deposited on Si(100) substrates in the temperature range of 400 - 500 °C by combination of micro-contact printing (μCP) and metalorganic chemical vapour deposition (MOCVD) methods. The patterned Si(100) substrates were initially fabricated with the self-assembled monolayers (SAMs) using an organic molecule of octadecyltrichlorosilane (OTS) by μCP method. Ta(N(MeEt))3(NtBu) and NH3 were used for the growth of TaN thin film. For a selective growth study, we characterized the as-grown films with optical microscopy (OM), micro-Raman spectrometer and atomic force microscopy (AFM). In the beginning of film deposition TaN thin film preferred to grow on silicon surface area rather than OTS printed area due to hydrophilicity of silicon surface, however, the selectivity of TaN thin film deposition was depended on the deposition time in the deposition temperature range.

The influence of the growth temperature and interruption time on the crystal quality of InGaAs/GaAs QW structures grown by MBE and MOCVD methods

The impact of two technological parameters, i.e., the growth temperature and the interface growth interruption, on the crystal quality of strained InGaAs/GaAs quantum well (QW) structures was studied. The investigated heterostructures were grown by molecular beam epitaxy (MBE) and metalorganic chemical vapour deposition (MOCVD) under As-rich conditions. Photoluminescence (PL), reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) were adopted for the evaluation of specified interfaces smoothness and the quality of layers. Comparison between both epitaxial techniques allowed us to find, that the growth temperature plays more significant role in the case of structures grown by MBE technique, whereas the quality of MOCVD grown structures is more sensitive to the growth interruption. Optimum values of the investigated parameters of QW crystallization were obtained for both growth techniques.

Effects of different ions implantation on yellow luminescence from GaN

The influence of C, N, O, Mg, Si and co-implants (Mg+Si) ions implantation with fluences in the wide range 10 13–10 17 cm −2 on the yellow luminescence (YL) properties of wurtzite GaN has been studied by photoluminescence (PL) spectroscopy. Two types of n-type GaN samples grown by metal-organic chemical vapor deposition method (MOCVD) and labeled as No-1 and No-2 were studied. In their as-grown states, No-1 samples had strong YL, while No-2 samples had weak YL. Results of the frontside and backside PL measurements in one of the as-grown GaN epifilms are also presented. Comparing the intensity of YL between frontside and backside PL spectra, the backside PL spectrum shows the more intense YL intensity. This implies that most of the intrinsic defects giving rise to YL exist mainly near the interface between the epilayer and buffer layer. Our experimental results show that the intensity ratio of YL to near-band-edge UV emission ( I YL/ I UV) decreases gradually by increasing the C implantation fluence from 10 13 to 10 16 cm −2 for No-1 samples after annealing at 900 °C. When the fluence is 10 17 cm −2, a distinct change of the I YL/ I UV is observed, which is strongly increased after annealing. For No-2 samples, after annealing the I YL/ I UV decreases gradually with increase in the C implantation fluence from 10 13 to 10 15 cm −2. The I YL/ I UV is gradually increased with increasing C fluence from 10 16 to 10 17 cm −2 after annealing, while I YL/ I UV for other ions-implanted GaN samples decreases monotonically with increase in the ions implantation fluences from 10 13 to 10 17 cm −2 for both No-1 samples and No-2 samples. It is noted that for annealed C-implanted No-2 samples I YL/ I UV is much higher than that of the as-grown one and other ion-implanted ones. In addition, I YL/ I UV for the Mg, Si, and co-implants (Mg+Si) implanted No-2 samples with a fluence of 10 13 cm −2 after being annealed at 900 °C is higher than that of the as-grown one. Based on our experimental data and literature results reported previously, the origins of the YL band have been discussed.

Cross-sectional transmission electron microscopy observations of structural damage in Al0.16Ga0.84N thin film under contact loading

This article reports a nanomechanical response study of the contact-induced deformation behavior in Al0.16Ga0.84N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. Al0.16Ga0.84N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young’s modulus of the Al0.16Ga0.84N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young’s modulus are 19.76±0.15 and 310.63±9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple “pop-ins” observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved.

Electrical transport studies of individualIrO2 nanorods and their nanorod contacts

We have studied the electrical transport properties of individual single-crystallineIrO2 nanorods prepared by the metal–organic chemical vapour deposition method. With thehelp of the standard electron-beam lithographic technique, individual nanorods arecontacted by Cr/Au submicron electrodes from above. Utilizing two-probe, three-probe andfour-probe measurement configurations, not only the intrinsic electrical transportproperties of the individual nanorods but also the electronic contact resistances,Rc(T), have been determined from 300 K down to liquid-helium temperatures. Our measuredresistivity behaviour of the nanorods is in close agreement with the current theoreticalunderstanding of this rutile material. On the other hand, we found that the temperaturebehaviour of the electronic contact resistance obeys the law over an extremely wide temperature range, from approximately 100 K down toliquid-helium temperatures. This latter conduction process is ascribed to the hopping ofelectrons through nanoscale Cr granules and/or an amorphous coating incidentallyformed at the interface between the submicron Cr/Au electrode and the nanorod.

Effect of Graded AlxGa1-xN Interlayer Buffer on the Strain of GaN Grown on Si (111) Using MOCVD Method

ABSTRACTGaN film grown on Si substrate with AlN/AlxGa1−xN buffer is studied by low pressure metal organic chemical vapor deposition (MOCVD) method. The AlxGa1−xN film with Al composition varying from 0∼ 0.66 was used. The correlation of the Al composition in the AlxGa1−xN film with the stress of the GaN film grown was studied using high resolution X-ray diffraction including symmetrical and asymmetrical ω/2θscans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1−xN buffer layer, crack-free GaN films can be successfully grown on Si (111) substrates using AlN and AlxGa1−xN buffer layers.

Microstructure and mechanical properties of hot-pressing chromium carbide/alumina nanocomposite prepared by MOCVD in fluidized bed

Nanocomposites of Cr 3C 2/Al 2O 3 were prepared by metal-organic chemical vapor deposition (MOCVD) method in a fluidized bed and sintered under hot-pressed condition at 1500 °C for1 h. The TEM microstructure showed that the Al 2O 3 matrix contained both intragranular and intergranular phase of Cr 3C 2. The hot-pressed Cr 3C 2/Al 2O 3 nanocomposites possessed better mechanical performance as regard to bending strength and fracture toughness in comparison to the monolithic Al 2O 3. The phenomenal change of the fracture mode from intergranular fracture of monolithic Al 2O 3 to transgranular fracture of nanocomposites is attributed to the enhancement of the residual stress and formation of a solid solution, eventually improving the strength of the Cr 3C 2/Al 2O 3 nanocomposite. Furthermore, it has been deciphered that the toughening mechanisms of the nanocomposites contribute to the crack deflection and the residual stress.