Metalorganic Chemical Vapor Deposition Method Research Articles

Effect of Growth Temperature and Mn Incorporation on GaN:Mn Thin Films Grown by Plasma-Assisted MOCVD

In this paper, the growth of GaN:Mn thin films by plasma-assisted metalorganic chemical vapor deposition (PAMOCVD) method is reported. The method used in this study, utilizes a microwave cavity as a cracking cell to produce nitrogen radicals, which in turn reduce the growth temperature. Trimethylgallium (TMGa), nitrogen (N2) and cyclopentadienyl manganese tricarbonyl (CpMnT) were used as a source of Ga, N and Mn, respectively, while hydrogen gas was used as a carrier gas for both TMGa and CpMnT. The effect of growth temperature and Mn incorporation on structural properties and surface morphology of GaN:Mn films are presented. The growth of GaN:Mn thin films were conducted at varied growth temperature in range of 625 o C to 700 o C and the Mn/Ga molar fraction in the range of 0.2 to 0.5. Energy dispersive of X-ray (EDX) and X-ray diffraction (XRD) methods were used to analyze atomic composition and crystal structure of the grown films, respectively. The surface morphology was then characterized using both atomic force microscopy (AFM) and scanning electron microscopy (SEM) images. A systematic XRD analysis reveal that maximum Mn incorporation that still produces single phase GaN:Mn (0002) is 6.4 % and 3.2 % for the film grown at 650 o C and 700 o C, respectively. The lattice constant and full width at half maximum (FWHM) of the single phase films depend on the Mn concentration. The decrease in lattice constant accompanied by the increase in FWHM is due to incorporation of substitutional Mn on the Ga sub-lattice. The maximum values of doped Mn atoms incorporated in the wurtzite structure of GaN:Mn as substitutional atoms on Ga sub-lattice are 2.0 % and 2.5 % at 650 o C and 700 o C, respectively. AFM and SEM images show that the film grown at lower growth temperature and Mn concentration has a better surface than that of film grown at higher growth temperature and Mn concentration.

Selective deposition of metal oxide thin films on Si(100) surfaces by combination of metal-organic chemical vapour deposition and microcontact printing methods

TiO2, ZrO2 and HfO2 thin films have been deposited selectively using metal-organic chemical vapour deposition (MOCVD) technique with various single molecular precursors on Si(100) substrates which were patterned with octadecyltrichlorosilane (OTS) applied by microcontact printing (μ CP). Titanium (IV) isopropoxide [Ti(OiPr)4], bis-isopropoxy-bis-tertiarybutyl- acetoacetate zirconium [Zr(OiPr)2 (tbaoac)2 ] and hafnium tert-butoxide [Hf(OtBu)4 ] were used for titanium dioxide (TiO2), hafnium and zirconium oxide (ZrO2 and HfO2) thin films, respectively. Selective depositions were successfully carried out in a home-made MOCVD system. All the deposited thin films had higher reactivity on bare silicon surfaces than OTS self-assembled monolayers (SAMs) deposited area. However, there was slightly different selective growth tendency on OTS deposited Si(100) surfaces. The selectivity tendency of the deposited thin films was revealed in order of TiO2, HfO2 and ZrO2. This tendency was explained by means of film growth rate, structures and molecular weight of precursors and acidity of transition metal of precursors.

Growth of FeSe on general substrates by metal-organic chemical vapor deposition and the application in magnet tunnel junction devices

Single-phase tetragonal FeSe films were grown on c-plane sapphire, SiO 2, GaAs (100) and Si (100) substrates by low-pressure metal-organic chemical vapor deposition method. X-ray diffraction analysis shows that all the FeSe thin films on different substrates are of (00l) orientation. Spin-dependent magnet tunnel junction with Fe/ZnSe/FeSe structure were fabricated, and the tunneling magnetic resistance ratio decreased with increasing the thickness of ZnSe layer in the range of 10–20 nm.

Structural and optical properties of SnO 2 films grown on α-Al 2O 3(0 0 0 1) by MOCVD

High-quality single crystalline SnO 2 films have been prepared on α-Al 2O 3(0 0 0 1) substrates by the metalorganic chemical vapor deposition (MOCVD) method. Structural and optical properties of the SnO 2 films prepared at different substrate temperatures (500–800 °C) were investigated in detail. The obtained films were pure SnO 2 with the tetragonal rutile structure. The film prepared at 600 °C showed the best single crystalline structure with a single orientation along a-axis. The average transmittance for the SnO 2 films in the visible range was over 90% with a minimum optical gap of 3.58 eV.

Preparation and characterization of single crystalline SnO 2 films deposited on α-Al 2O 3 (0001) by MOCVD

High-quality single crystalline SnO 2 thin films have been prepared on α-Al 2O 3 (0001) substrates by the metalorganic chemical vapor deposition (MOCVD) method. Structural, electrical and optical properties of the SnO 2 films prepared at different substrate temperatures (500 °C–800 °C) have been investigated in detail. The obtained films were pure SnO 2 with the tetragonal rutile structure. The film prepared at 600 °C showed the best single crystalline structure with a clear epitaxial relationship of SnO 2 (100)||Al 2O 3 (0001). The highest Hall mobility of the SnO 2 films was 27.67 cm 2 V − 1 s − 1 , and the average transmittance of the films in the visible range was over 90%.

Transparent conducting SnO 2:Sb epitaxial films prepared on α-Al 2O 3 (0001) by MOCVD

Antimony-doped tin oxide (SnO 2:Sb) single crystalline films have been prepared on α-Al 2O 3 (0001) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The antimony doping was varied from 0 to 7% (atomic ratio). The structural, electrical and optical properties of the films were investigated in detail. The prepared samples were epitaxial single crystalline films with the rutile structure of pure SnO 2. Film with resistivity of 9.1 × 10 − 4 Ω cm, carrier concentration of 5.33 × 10 20 cm − 3 and Hall mobility of 12.73 cm 2 v − 1 s − 1 was obtained at 5% of Sb concentration. The average transmittance for the SnO 2:Sb films in the visible range was over 90%.

Study on the Energy-Band Structure of Indium-Rich InGaN/GaN Quantum Dot System

The ground-state energy levels and energy band structures of the In-rich InGaN/GaN quantumdot (QD) system were analyzed by performing the capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS), and photoluminescence (PL) measurements. The InGaN QD system was grown by using a metal-organic chemical vapor deposition method. The lateral size, the height, and the density of a disc-shaped InGaN QDs were 47.3 nm, 1.2 nm and 9.0 ◊ 10 9 cm 2 , respectively. The ground states of the InGaN QDs were located at 0.44 eV from the top of the barrier, which correspond to the conduction band edge of GaN. The QDs had various levels, except for the ground-state energy. A band-to-band transition energy of 2.92 eV was found by using PL measurements. Moreover, antisite point defects were also founded in GaN buer layer, and their activation energy and emission cross-section were 0.70 eV and 1.19 ◊ 10 13 cm 2 , respectively.

Donor/acceptor doping and electrical tailoring in ZnO quantum dots

The authors report on donor/acceptor doping in ZnO quantum dots (QDs) grown by a metal-organic chemical vapor deposition method. The Ga donor and N acceptor, as identified by x-ray photoelectron spectroscopy (XPS), are introduced into ZnO QDs. They demonstrate, with a combination of valence band XPS and scanning tunneling microscopy, that the electrical properties as well as Fermi level of the ZnO QDs can be well tuned by the donor/acceptor doping. In addition, photoluminescence from the ZnO QDs with quantum confinement effect is observed.

Enhancement of blue emission from GaN films and diodes by water vapor remote plasma treatment

We have studied the effects of water vapor remote plasma treatment (H 2O RPT) on emission from Si-doped and undoped n-type GaN films grown on c-face sapphire substrates by the atmospheric-pressure metalorganic chemical vapor deposition method. We found by photoluminescence (PL) spectroscopy at 77 K that H 2O RPT enhanced violet emission from the n-type GaN films, similarly to the previously observed enhancing effect on blue emission from Mg-doped p-type GaN films. We also observed that H 2O RPT reduced the intensity of ESR signal comprising of two peaks detected at 4.2 K in undoped n-type films and increased their resistivity measured at room temperature. We ascribe the enhancing effect of H 2O RPT to the passivation of non-radiative recombination centers by hydrogen produced by H 2O RPT. We formed GaN p–n diodes from the layer structure of p-GaN:Mg/n-GaN:Si/sapphire, and carried out electroluminescence (EL) measurements of the diodes at 77 K. We observed that EL intensity was also enhanced by H 2O RPT.

Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates

Titanium oxide (TiO 2) and zirconium oxide (ZrO 2) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(O i Pr) 2(tbaoac) 2] (M=Ti, Zr; tbaoac=tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (μCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has –CH 3 terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO 2 and ZrO 2 were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300–500 °C and deposition pressure of 1×10 −3–3×10 −2 Torr. N 2 gas (5 sccm) was used as a carrier gas during film depositions. TiO 2 and ZrO 2 thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO 2 or Si–OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.

Berkovich nanoindentation and deformation mechanisms in GaN thin films

The deformation mechanisms of GaN thin films obtained by metal-organic chemical vapor deposition (MOCVD) method were studied using nanoindentation with a Berkovich diamond indenter, micro-Raman spectroscopy and the cross-sectional transmission electron microscopy (XTEM) techniques. Due to the sharpness of the tip of Berkovich indenter, the nanoindentation-induced deformation behaviors can be investigated at relatively lower load and, hence, may cover wider range of deformation-related phenomena over the same loading range. The load–displacement curves show the multiple “pop-ins” during nanoindentation loading. No evidence of nanoindentation-induced phase transformation and cracking patterns were found up to the maximum load of 300 mN, as revealed from the micro-Raman spectra and the scanning electron microscopy (SEM) observations within the mechanically deformed regions. In addition, XTEM observation performed near the cross-section of the indented area revealed that the primary deformation mechanism in GaN thin film is via propagation of dislocations on both basal and pyramidal planes. The continuous stiffness measurement (CSM) technique was used to determine the hardness and Young's modulus of GaN thin films. In addition, analysis of the load–displacement data reveals that the values of hardness and Young's modulus of GaN thin films are 19 ± 1 and 286 ± 25 GPa, respectively.

Selective growth of iron oxide thin films using the combined method of metal-organic chemical vapor deposition and microcontact printing

The authors have carried out the selective deposition of magnetite iron oxide (Fe3O4) thin films with about 50nm thickness on Si(100) surfaces which were patterned by octadecyltrichlorosilane (OTS) using microcontact printing (μCP) method. The μCP method showed that hydrophobic patterns with microdimension were able to be formed on hydrophilic area such as silicon surface. Iron oxide thin films were deposited on the Si(100) substrates by thermal metal-organic chemical vapor deposition (MOCVD) method using single molecular organometallic precursor of iron pentacarbonly [Fe(CO)5] with high purity (99.999%) oxygen gas. The deposition was performed in the range of 250–350°C substrate temperature for 2–10min under 1×10−2Torr in a homemade MOCVD system. In order to check the selectivity of as-deposited thin films optical microscopy, scanning electron microscopy, and atomic force microscopy analyses were performed. To confirm the crystallinity of deposited thin films, x-ray diffraction patterns and micro-Raman were studied. Also energy dispersive x-ray and x-ray photoelectron spectrometry results showed the composition of the as-grown iron oxide thin films. By means of these results, the authors can suggest the selective deposition mechanisms and tendencies of iron oxide thin films onto the OTS patterned Si(100) surfaces.

Effect of Source Supply Methods on Low-Temperature Preparation of Lead Zirconate Titanate Thin Films Using SrTiO<sub>3</sub> Seed Layers by Metallorganic Chemical Vapor Deposition

Pb(Zr, Ti)O3 thin films were successfully prepared on (111)Pt/IrO2/SiO2/(100)Si substrates using SrTiO3 seeds at 290 oC by RF inductive heating type and 350 oC by resistive heating type metalorganic chemical vapor deposition method (MOCVD), respectively. The SrTiO3 was chosen as seed layers and prepared by pulsed laser deposition method. The crystal structures and orientations of SrTiO3 seeds were changed by deposition temperature. In the case of preparation with RF inductive heating MOCVD, the remanent polarization (2Pr) and coercive field (2Ec) were 42 μC/cm2 and 256 kV/cm, respectively.

OTS-Templated Cobalt Deposition Using Co<sub>2</sub>(CO)<sub>8</sub> Precursor

We have investigated selective deposition of Co thin films on the OTS-patterned glass surface by using μ-CP(Micro-Contact Printing) coupled with MOCVD(Metal Organic Chemical Vapor Deposition) method with Co2(CO)8 as a Co precursor. Co thin films in the thickness of 5-180 nm has been selectively formed on the glass surface in the presence of the OTS(Octadecyltrichlrosilane) monolayer at the temperatures 60-90, at the pressure of 0.03-0.6 Torr. The self-assembled OTS monolayer on the surface passivates the surface hydroxyl(-OH), adsorption sites for Co precursors, and thus significantly increases the induction period to nucleate Co metals on the OTS monolayer, compared with on the bare glass. Lowering the temperature and the processing pressure is likely to increase the difference in the induction period for the two substrate surfaces and thus improves the selectivity. About 180 nm-thick Co thin film was selectively formed on the OTS-patterned glass at 70, however, lowering the temperature to 60 decreased the thickness, which is attributed to the reduced growth rate of Co at the lower temperature. The Co thin films deposited at 60-90 and at 0.03-0.6 Torr have the resistivities of 10-20 μ4-cm and are free of contamination. Consequently, the low temperature process for the selective deposition of Co in the presence of the OTS monolayer can be utilized for a variety of applications including flexible electronics and semiconductor devices.

Deposition of Yb2O3 buffer films using H2O vapor by MOCVD method

Yb2O3 films were successfully deposited on (100) SrTiO3 (STO) single crystal substrates and on a cube-textured Ni–5at%W by MOCVD (metal organic chemical vapor deposition) method. H2O vapor was used as an oxidant in order to avoid the oxidation of Ni substrate. The working pressure, Ar flow rate and H2O vapor flow rate were 10Torr, 600sccm and 700sccm, respectively. Epitaxial Yb2O3 (400) films were deposited on STO substrates at high temperatures above 950°C, while small Yb2O3 (222) peak from XRD was detected below 920°C. The AFM surface roughness of Yb2O3 film grown on STO was in the range of 10nm for the film deposited at 950°C with a H2O vapor partial pressure of 5.5Torr and deposition time of 5min. For cube-textured Ni–5at%W substrate, both Yb2O3 (222) and Yb2O3 (400) textures were grown at deposition temperatures above 850°C. The Δϕ values of Yb2O3/STO were in the range of 2–3°, while Yb2O3/Ni–5at%W were in the range of 8–10.5.

Residual impurities in GaN substrates and epitaxial layers grown by various techniques

Low-temperature/high-resolution photoluminescence spectra of thick freestanding hydride vapor-phase epitaxial GaN substrates show intense sharp lines in the near bandedge spectral region, which has been previously assigned to recombination processes associated with the annihilation of excitons bound to neutral Si and O donors. Similar studies carried out on unintentionally doped (UID) and Si-doped homoepitaxial films grown by molecular beam epitaxy and metalorganic chemical vapor deposition methods, respectively, supports the previous identification of Si and O as the dominant shallow donors in UID GaN. The chemical nature of these background impurities and dopants were verified by high sensitivity secondary ion mass spectroscopy. The present work confirms Si and O as the pervasive dominant shallow donors in UID GaN and demonstrate the usefulness of photoluminescence as a non-destructive technique to identify impurities in GaN.

Sterilization effects of a TiO2 photocatalytic film against aStreptococcus mutans culture

Streptococcus mutans is one of the more significant pathogens involved in the development of dental caries in humans. The purpose of this research was to design a TiO2-coated dental instrument and to determine the bactericidal effects of the instrument onS. mutants. TiO2 photocatalytic films were prepared by the low-pressure metal-organic chemical vapor deposition (LPMOCVD) method using titanium tetraisopropoxide (TTIP) as precursor. The photocatalytic reaction was carried out on a TiO2-coated pyrex petri dish with an ultraviolet (UV) light emitting diode (LED) illuminator or a fluorescent lamp light source. Our data indicates that the relative survival ratio ofS. mutans when plated onto TiO2 photocatalytic films and under exposure to UV-A light for 15 min was 0.01%. In addition, a fluorescent lamp light source also had bactericidal effects on theS. mutans plated TiO2 photocatalytic films. These results indicate that TiO2-coated dental materials or devices may be useful in dental treatments for the prevention of carious or enamel demineralization.

Hybrid II-VI and III-V Compound Double Heterostructures and Their Properties

In this report, n-GaN/n-ZnO/p-GaN double heterostructures (DHs) were grown on sapphire substrate employing metal-organic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE) methods. Scanning electron microscopy (SEM) employed in both secondary electron (SE) and cathodoluminescence (CL) modes revealed high crystal and optical quality of the DH layers, indicating no significant interdiffusion of constituent elements during growth. The diode structures were fabricated whose current-voltage characteristics revealed rectifying behavior with a leakage current 2.12 × 10−5 A and a forward current 7.8 × 10−2 A at 10 V bias, and with threshold and breakdown voltages of 3.2 and –11 V, respectively. Under forward bias, an intense electroluminescence (EL) was observed, the spectrum of which depended on the injection current.

Deposition of CuInS2 Thin Films Using Copper- and Indium/Sulfide-Containing Precursors through a Two-Stage MOCVD Method

Copper indium disulfide (CuInS2; CIS) films were deposited on various substrates by two-stage metal-organic chemical vapor deposition (MOCVD) at relatively mild conditions, using Cu- and In/S-containing precursors without toxic H2S gas: first, a pure Cu thin film was prepared on glass or indium/tin oxide glass substrates by using a single-source precursor, bis(ethylbutyrylacetato)copper(II) or bis(ethylisobutyrylacetato)copper(II); second, on the resulting Cu film, tris(N,N-ethylbutyldithiocarbamato)indium(III) was treated to produce CIS films by a MOCVD method at 430 degrees C. In this process, their thicknesses and stoichiometries were found to be elaborately controlled on demand by adjusting the process conditions. The optical band gap of the stoichiometric CIS film was about 1.41 eV, which is in the near-optimal range for harvesting solar radiation energy.

Preparation of CdS Thin Films through MOCVD Method, Using Cd-S Single-source Precursors

Numerous physical properties of CdS films notablydepend on their deposition methods and the particularconditions of preparation processes. They can be preparedby chemical, physical and electrochemical methods such asmolecular beam epitaxy (MBE); metal organic chemicalvapor deposition (MOCVD); close-spaced sublimation (CSS);chemical bath deposition (CBD); electro-deposition; succe-ssive ionic layer adsorption and reaction (SILAR); screenprinting; pulsed laser ablation; RF sputtering; and spraypyrolysis.