Assisted Metal Organic Chemical Vapor Research Articles

Surface and optical properties of indium-rich InGaN layers grown on sapphire by migration-enhanced plasma assisted metal organic chemical vapor deposition

In-rich InGaN nanoscale thin films grown on (0001) sapphire (Al2O3) using migration enhanced plasma-assisted metal-organic chemical vapor deposition (MEPA-MOCVD) method are characterized by high-resolution x-ray diffraction (HR-XRD), x-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy (RSS), as well as variable angle spectroscopic ellipsometry (VASE). Theoretical calculations were performed to acquire the optical constants and vibrational properties of the films. The indium composition x (In) values determined by HR-XRD and from the surface area calculated by XPS are in good agreement with each other. The valence band maxima of InxGa1−xN films (x = 0.65–0.80) were observed to shift to lower binding energy with the increase of indium concentration. The RSS results confirmed the one-phonon behavior for the A1(LO) and E2(high) modes with x (In)—independent of phonon frequencies of the substrate. The simulated refractive index n was found to increase with In composition, the band gap (Eg) shifted, however, towards the lower energy side. For a given In composition and by increasing the measurement temperature from 30 °C to 600 °C, the variations of optical constants (n and Eg) showed similar trends as in samples with increasing In composition.

Synthesis, crystal structure and vapour pressure studies of novel nickel complex as precursor for NiO coating by metalorganic chemical vapour deposition technique

A square planar nickel complex namely bis(N-propyl-3-methylsalicylaldimine)nickel(II) (2) was prepared from its parent compound bis(3-methylsalicylaldehydato)nickel(II) (1) by adding n-propylamine in a methanol medium. The TG/DTA analysis of the resultant Schiff's base complex 2 in the solid phase was evaluated in an inert N2 environment at atmospheric pressure. Complex 2 was completely volatile giving nil residue at 335 °C in a single weight loss step, whereas the complex 1 was found to be non-volatile giving 47% residues till 455 °C. The change in volatility of 2 was brought about by the condensation of n-propylamine with 1 which replaced aldehyde O (-CH=O) with N (-CH=N). The volatile precursor 2 was characterised by single crystal XRD, 1H and 13C NMR, FT-IR, C, H and N elemental analysis and mass spectrometry. The temperature dependence of the saturated vapour pressure and enthalpy of vapourisation (ΔvapH° = 97.9 ± 2.0 kJ mol−1) of the volatile complex 2 was determined by a transpiration TG technique in the temperature range 499–562 K. Subsequently, it was used as a precursor for the deposition of nickel oxide (NiO) thin film on Si(100) substrate by employing plasma assisted metal-organic chemical vapour deposition (PAMOCVD) technique. The nano-crystalline nickel oxide thin films were analysed by XRD and SEM/EDX. X-ray photoelectron spectroscopy (XPS) study confirmed the formation of stoichiometric NiO phase. The band gap of the NiO thin film was found to be 4.31eV exhibiting a blue shift as observed from DRS-UV.

Deposition of ZnO based thin films by atmospheric pressure spatial atomic layer deposition for application in solar cells

The use of Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) has gained popularity in the last decade. The success of this technique relies on the possibility to deposit thin films in a fast, vacuum-free, low-cost, low-damage, and high throughput way. In this work, we present ZnO and Aluminium doped ZnO (AZO) films deposited by AP-SALD at low temperature (<220 °C) with high uniformity and conformity. The ZnO films present a high transparency of 80%–90% in the visible range, with a tuneable band-gap, between 3.30 eV and 3.55 eV, controlled by the deposition temperature. The carrier density reaches values greater than 3 × 1019 cm−3, while the electron mobility of the films is as high as 5.5 cm2 V−1 s−1, resulting in an optimum resistivity of 5 × 10−2 Ω cm. By doping ZnO with aluminium, the resistivity decreases down to 5.57 × 10−3 Ω cm, as a result of a significant increase in the carrier density up to 4.25 × 1020 cm−3. The combination of ZnO thin films with p-type cuprous oxide (Cu2O), deposited by aerosol assisted metal organic chemical vapor deposition, allowed the formation of oxide-based pn junctions. The dark I-V characteristic curve confirms a rectifying behaviour, opening the window for the production of all-oxide solar cells completely by chemical vapour deposition methods. We also show the potential of AP-SALD to deposit AZO as a transparent conductive oxide layer for silicon heterojunction solar cells.

Effect of Co Doping on the Galvanomagnetic Properties of ZnO Thin Films

The influence of the Co doping on the properties of zinc oxide films was investigated. The films were grown by oxygen and water assisted metal organic chemical vapor deposition (MOCVD). The large positive magnetoresistance (PMR) was observed in Co doped films at low temperatures while the negative magnetoresistance was observed in undoped ZnO films deposited under the same conditions. The relative variation of resistivity was comparable in the films grow by oxygen and water assisted MOCVD although the resistivity and its temperature dependence were significantly different. The magnitude of PMR increases with an increase of the Co content and with the decrease of temperature.

Features of the hopping conductivity in gallium and cobalt doped ZnO thin films

The effect of Ga and Co doping on the hopping transport of electrons in ZnO films was studied. All investigated films were deposited on monocrystalline substrates by water assisted metal organic chemical vapour deposition method. Temperature dependencies of the resistivity of all films obeyed the Mott's law at low temperatures. Both positive and negative magnetoresistance were observed in the temperature range of the Mott's law. The values of the localization length obtained from magneto transport data for ZnO and ZnO:Ga films are larger than the effective Bohr radii of a shallow donor state and are independent on the Ga content. These observations point to the localization of electrons in the random potential originating from the structural disorder. In Co doped ZnO films large positive magnetoresistance was observed in low magnetic fields at low temperatures. The value of positive magnetoresistance increases with an increase of Co content and decrease of temperature. Observed magneto transport properties of Co-doped films were interpreted by the decrease of electron hopping probability due to decrease of the density of localized states in magnetic field.

RF plasma MOCVD of Y2O3 thin films: Effect of RF self-bias on the substrates during deposition

Yttrium oxide (Y2O3) thin films have been deposited by radio frequency plasma assisted metal organic chemical vapor deposition (MOCVD) process using (2,2,6,6-tetramethyl-3,5-heptanedionate) yttrium (commonly known as Y(thd)3) precursor in a plasma of argon and oxygen gases at a substrate temperature of 350°C. The films have been deposited under influence of varying RF self-bias (−50V to −175V) on silicon, quartz, stainless steel and tantalum substrates. The deposited coatings are characterized by glancing angle X-ray diffraction (GIXRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry and scanning electron microscopy (SEM). GIXRD and FTIR results indicate deposition of Y2O3 (BCC structure) in all cases. However, XPS results indicate nonstoichiometric cubic phase deposition on the surface of deposited films. The degree of nonstoichiometry varies with bias during deposition. Ellipsometry results indicate that the refractive index for the deposited films is varying from 1.70 to 1.83 that is typical for Y2O3. All films are transparent in the investigated wavelength range 300–1200nm. SEM results indicate that the microstructure of the films is changing with applied bias. Results indicate that it is possible to deposit single phase cubic Y2O3 thin films at low substrate temperature by RF plasma MOCVD process. RF self-bias that decides about the energy of impinging ions on the substrates plays an important role in controlling the texture of deposited Y2O3 films on the substrates. Results indicate that to control the structure of films and its texture, it is important to control the bias on the substrate during deposition. The films deposited at high bias level show degradation in the crystallinity and reduction of thickness.

Transparent Conducting ZnO:B Thin Films Grown by Ultraviolet Light Assisted Metal Organic Chemical Vapor Deposition Using Triethylboron for Cu(In,Ga)Se2Solar Cells

Transparent Conducting ZnO:B Thin Films Grown by Ultraviolet Light Assisted Metal Organic Chemical Vapor Deposition Using Triethylboron for Cu(In,Ga)Se₂Solar Cells

Transparent Conducting ZnO:B Thin Films Grown by Ultraviolet Light Assisted Metal Organic Chemical Vapor Deposition Using Triethylboron for Cu(In,Ga)Se2 Solar Cells

High-efficiency cadmium-free Cu(In,Ga)Se2 (CIGS) thin-film solar cells have been fabricated using a zinc compound buffer layer deposited by the chemical bath deposition (CBD) process. However, the zinc compound buffer layers such as ZnS(O,OH) are prone to plasma-induced damage during the subsequent ZnO sputtering process. A process causing less damage such as metal–organic chemical vapor deposition (MOCVD) is thus required for ZnO-based transparent conducting oxide (TCO) layers. In the present work, the boron-doped zinc oxide (ZnO:B) films were grown by MOCVD using diethyl zinc (DEZ), H2O, and low-toxicity triethylboron (TEB). An UV-assisted MOCVD process was developed in order to reduce the resistivity of ZnO:B films. As a result, the resisitivity significantly decreased together with the increased electron mobility and carrier concentration. The comparison of performance was also carried out for the ZnS(O,OH)/CIGS solar cells with MOCVD-deposited ZnO:B and sputter-deposited ZnO:Al window layers.

Deposition of Ni/TiN Composite Coatings by a Plasma Assisted MOCVD Using an Organometallic Precursor

Titanium nitride (TiN)/nickel (Ni) composite coatings were synthesized by plasma assisted metal-organic chemical vapour deposition (PAMOCVD) using organo-metallic and metal-organic complexes namely dichlorobis(� 5 - cyclopentadienyl)titanium (IV) for titanium and N,N'-ethylene-bis(2,4-pentanedion-iminoato)nickel(II) for nickel. The growth of such films was investigated in nitrogen (N2) plasma environment in the substrate temperature range of 450- 550oC at a deposition pressure of 0.5-1 mbar. Prior to the deposition of films, the Ti precursor was subjected to the equilibrium vapour pressure measurements by employing TG/DTA in transpiration mode, which led to the value of 109.2 ± 5.6 kJ mol -1 for the standard enthalpy of sublimation (�H o sub). The phase identification using glancing incidence x-ray diffraction showed Ni/TiN is a nanocomposite coating containing nanocrystals of Ni and TiN with face centered cubic structure. Scanning electron microscopy revealed a uniform surface morphology of the films, while chemical analysis by energy dispersive analysis confirmed the presence of titanium, nickel and nitrogen in the composite films.

Passivation of Ge(100) and (111) Surfaces by Termination of Nonmetal Elements

The passivation of the Ge surface is an important issue for a high-performance transistor. Therefore, we carried out the theoretical and experimental analyses to search for alternative terminal materials on the Ge surface. First, the chemical reactivities of various nonmetal elements on the Ge surface were simulated by the semi empirical molecular orbital method to passivate the Ge(100) and (111) surface dangling bonds. The simulations showed that F, Cl, and Se are more useful for the treatment of the Ge(100) surface and that F, Cl, S, and Se are more stable on the Ge(111) surface than H. In particular, S is more effective in terminating the dangling bonds by forming a bridge bond (Ge–S–Ge) and more stable on the Ge(111) surface than on the Ge(100) surface. Next, for experimental confirmation, we performed an (NH4)2S solution treatment method on the p-type Ge(100) and (111) substrates, and fabricated HfO2/p-Ge metal–insulator–semiconductor (MIS) devices by photo assisted metal organic chemical vapor deposition (MOCVD). As a result, the S-treatment using (NH4)2S solution improved more the electrical properties of the HfO2/p-Ge(111) MIS capacitor than those of the capacitor on the Ge(100) substrate. Recently, the sulfur treatment of the Ge surface has been mainly focused on the Ge(100) substrate. However, the results of this study show that the sulfur treatment method using (NH4)2S solution is more useful on the Ge(111) surface than on the Ge(100) surface.

Modeling and Characterization of Silicon Nanowire Networks for Thermoelectric Conversion

ABSTRACTWe report the growth of silicon nanowires by plasma assisted metal organic chemical vapor deposition. Silicon nanowires grew as three-dimensional networks in which electrical charges and heat can travel over the distance much longer than the mean length of the constituent nanowires. We studied the dependence of thermoelectric properties on two factors; nominal doping concentrations and geometrical factors within the silicon nanowire networks. The silicon nanowire networks show Seebeck coefficients comparable with that of bulk silicon for a given nominal doping concentration, allowing us to control Seebeck coefficients by tuning the doping concentrations. Rather than studying single nanowires, we chose networks of nanowires formed densely across large areas required for large scale production. We also studied the role played by intersections where multiple nanowires were fused to form the nanowire networks. Structural analysis, transport measurement, and modeling based on finite-element analysis were carried out to obtain insights of physical properties at the intersections. Understanding these physical properties of three-dimensional nanowire networks will advance the development of thermoelectric devices.

Microwave ECR Plasma Assisted MOCVD of Y2O3 Thin Films Using Y(tod)3 Precursor and Their Characterization

AbstractYttrium oxide (Y2O3) thin films were deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process using indigenously developed metal organic precursors Yttrium 2,7,7‐trimethyl‐3,5‐octanedionates, commonly known as Y(tod)3 which were synthesized by an ultrasound method. A series of thin films were deposited by varying the oxygen flow rate from 1–9 sccm, keeping all other parameters constant. The deposited coatings were characterized by X‐ray photoelectron spectroscopy, glancing angle X‐ray diffraction and infrared spectroscopy. Thickness and roughness for the films were measured by stylus profilometry. Optical properties of the coatings were studied by the spectroscopic ellipsometry. Hardness and elastic modulus of the films were measured by nanoindentation technique. Being that microwave ECR CVD process is operating‐pressure‐sensitive, optimum oxygen activity is very essential for a fixed flow rate of precursor, in order to get a single phase cubic yttrium oxide in the films. To the best of our knowledge, this is the first effort that describes the use of Y(tod)3 precursor for deposition of Y2O3 films using plasma assisted CVD process. magnified image

Effects of precursor evaporation temperature on the properties of the yttrium oxide thin films deposited by microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition

Yttrium oxide thin films are deposited using indigenously developed metal organic precursor (2,2,6,6-tetra methyl-3,5-hepitane dionate) yttrium, commonly known as Y(thd) 3 (synthesized by ultrasound method). Microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition process was used for these depositions. Depositions were carried out at a substrate temperature of 350 °C with argon to oxygen gas flow rates fixed to 1 sccm and 10 sccm respectively throughout the experiments. The precursor evaporation temperature (precursor temperature) was varied over a range of 170–275 °C keeping all other parameters constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and refractive index of the coatings are measured by the spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique. C-Y 2O 3 phase is deposited at lower precursor temperature (170 °C). At higher temperature (220 °C) cubic yttrium oxide is deposited with yttrium hydroxide carbonate as a minor phase. When the temperature of the precursor increased (275 °C) further, hexagonal Y 2O 3 with some multiphase structure including body centered cubic yttria and yttrium silicate is observed in the deposited film. The properties of the films drastically change with these structural transitions. These changes in the film properties are correlated here with the precursor evaporation characteristics obtained at low pressures.

Effect of argon ion activity on the properties of Y 2O 3 thin films deposited by low pressure PACVD

Yttrium oxide thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition process using an indegeneously developed Y(thd) 3 {(2,2,6,6-tetramethyl-3,5-heptanedionate)yttrium} precursor. Depositions were carried out at two different argon gas flow rates keeping precursor and oxygen gas flow rate constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (GIXRD) and infrared spectroscopy. Optical properties of the films are studied by spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique. Stability of the film and its adhesion with the substrate is inferred from the nanoscratch test. It is shown here that, the change in the argon gas flow rates changes the ionization of the gas in the microwave ECR plasma and imposes a drastic change in the characteristics like composition, structure as well as mechanical properties of the deposited film.

Diagnostics of microwave ECR generated plasma: Effect of contaminated reference electrode

Langmuir probe diagnostics is performed on microwave ECR generated plasma that is routinely being used in our laboratory for plasma assisted chemical vapour deposition (CVD) and metal organic chemical vapour deposition (MOCVD) applications. Diagnostics is performed on Argon plasma when the plasma generation chamber was new and also after the prolonged use of this chamber for plasma assisted CVD applications. Clear differences in the values of plasma parameters from the two cases were observed and these differences are explained. The investigations reported here clearly indicate the important role of reference electrode in plasma diagnostics experiments and also suggest that it is very important to have the proper (uncontaminated) reference electrode during plasma diagnostics particularly when measurements are performed in the contaminated chamber.

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Abstract Yttrium oxide (Y2O3) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)3 synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y2O3 on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.

Effect of Mn Addition on In-Field Behavior of IBAD/MOCVD Gd-YBCO Second Generation HTS Tapes

We analyze the effect of Mn addition to Gd-substituted YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-delta</sub> (YBCO) on transport current and behavior under applied magnetic field. The high-temperature superconducting tapes were manufactured by ion-beam assisted deposition and metal organic chemical vapor deposition on hastelloy substrates. The field dependence measurements as a function of Mn concentration were performed in applied magnetic fields up to 1.5 T at 77 K. The dependence of critical current on the field angle was measured in the plane perpendicular to the sample longitudinal axis (current axis). The effect of Mn concentration on critical temperature is also reported. The results are characterized and discussed.

Realization of Ultraviolet Electroluminescence from ZnO Homojunction Fabricated on Silicon Substrate with p-Type ZnO:N Layer Formed by Radical N2O Doping

ZnO homojunction light-emitting diodes are fabricated on Si(100) substrates by plasma assisted metal organic chemical vapour deposition. A p-type layer of nitrogen-doped ZnO film is formed using radical N2O as the acceptor precursor. The n-type ZnO layer is composed of un-doped ZnO film. The device exhibits desirable rectifying behaviour with a turn-on voltage of 3.3V and a reverse breakdown voltage higher than 6V. Distinct electroluminescence emissions centred at 395 nm and 490 nm are detected from this device at forward current higher than 20 mA at room temperature.

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.

Preparation of conductive HfN by post rapid thermal annealing-assisted MOCVD and its application to metal gate electrode

Conductive hafnium nitride (HfN) with negligible carbon impurity (<0.1 at.%) was chemically synthesized for the first time by post-rapid thermal annealing (PRTA)-assisted metal organic chemical vapor deposition (MOCVD) method. The thermodynamic instability of N-rich hafnium nitride (Hf 3N 4) phase, which is considered to be the dominant phase in CVD deposition of hafnium nitride, was utilized for pure and metallic HfN synthesis. By integrating the PRTA-HfN film into MOS capacitor, the electrical properties of the PRTA-HfN film as metal gate electrode were studied. Well behaved electrical characteristics such as about 4.9 eV of effective work function, low leakage current and large reduction in SiO 2 equivalent oxide thickness (EOT), which was attributed to the combination of physical thinning of SiO 2 and formation of high- κ interfacial layer, suggest the potential capability of PRTA-assisted MOCVD in chemically synthesizing HfN metal gate electrode for pMOS devices application.