Metalorganic Chemical Vapor Deposition Method Research Articles

Study on ZrO2:Er Thin Films Fabricated by Metal-Organic Chemical Vapor Deposition

ZrO2:Er thin films for active waveguide applications were fabricated by the metal-organic chemical vapor deposition (MOCVD) method. X-ray diffraction demonstrated that there is a rapid change of preferred orientation, from (001) to (100), in samples of which the Er contents are 2.39 mol% and 10.41 mol%, respectively. The observed phase change from monoclinic to tetragonal was attributed to the c/a ratio reduction with Er ion incorporation into the ZrO2 matrix. A considerable increase in oxygen deficiency leads to the phase change, as revealed by X-ray photoelectron spectroscopy (XPS). The near-infrared photoluminescence of 4I13/2 → 4I15/2 transition was investigated and the quenching concentration for the luminescence was found to be 2.39 mol%. It was proposed that the oxygen deficiency observed at 10.41 mol% Er concentration is mainly responsible for the quenching phenomenon.

Highly stable and textured hydrogenated ZnO thin films

We investigated intentionally hydrogenated zinc oxide (ZnO:H) fabricated by combining photoassisted metalorganic chemical vapor deposition and mercury-sensitized hydrogen addition methods. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved surface roughness of the ZnO:H film due to an enhancement of (112̄0) orientation. The high-quality ZnO:H film is promising as a back reflector material for thin-film solar cells.

Epitaxial growth of high quality ZnO:Al film on silicon with a thin γ-Al2O3 buffer layer

ZnO:Al thin films were grown epitaxially on epi-γ-Al2O3/Si (111) substrates by rf sputtering and pulsed laser deposition. The γ-Al2O3 buffer layer was deposited on Si (111) at a low substrate temperature of 500 °C using the metalorganic chemical vapor deposition method. Reflection high energy electron diffraction and x-ray diffraction measurements indicated a near alignment of the ZnO:Al epilayer on γ-Al2O3/Si (111) as compared to those grown directly on Si (111). Atomic force microscopy results of the films ZnO:Al/γ-Al2O3/Si (111) deposited by pulsed laser deposition revealed a smoother surface in comparison with the films deposited by rf sputtering. The M band observed in the photoluminescence spectra of the films deposited by laser ablation suggests that high quality epitaxial ZnO:Al/γ-Al2O3/Si (111) films can be deposited by pulsed laser deposition.

Growth of Structured Non-crystalline Boron-Oxygen-NitrogenFilms and Measurement of Their Electrical Properties

The boron-oxygen-nitrogen (BON) films have been grown on Siwafer by the low-frequency rf-plasma-enhanced metal-organic chemicalvapour deposition method. The homogeneous film structure of completelyamorphous BON is first fabricated on a low-temperature-made buffer at500°C with N2 plasma and is observed with a high-resolution-electron microscope by the transmission-electron diffraction. Theresults show that the interfaces among substrate/buffer/film are clearand straight in the structured film. A heterogeneous film containingnano-sized crystalline particles is also grown by a routine growthprocedure as a referential structure. The C-V characteristicis measured on both the amorphous and crystal-containing films by usingthe metal-oxide-semiconductor structure. The dielectric constants ofthe films are, therefore, deduced to be 5.9 and 10.5 for the amorphousand crystal-containing films, respectively. The C-V resultsalso indicate that more trapped charges exist in the amorphous film.The binding energy of the B, O, and N atoms in the amorphous film ishigher than that in the crystal-containing one, and the N-content inthe latter is found to be higher than that in the former by x-rayphoto-electron spectroscopy. The different electrical property of thefilms is thought to originate from the energy state of the covalentelectrons.

Deposition of CeO 2 and NiO buffer layers for YBCO coated conductors on biaxially textured Ni substrates by a MOCVD technique

CeO 2 and NiO buffers for YBCO coated conductors were deposited on biaxially textured Ni substrates by a metal-organic chemical vapor deposition method. The degree of texture and surface roughness of the oxide films were analyzed by X-ray pole figure, atomic force microscope (AFM) and scanning electron microscopy. The texture of deposited CeO 2 films was a function of deposition temperature and oxygen partial pressure ( P O 2 ). The (2 0 0) texture of CeO 2 was fully developed at T=500–520 °C and P O 2 =3.33 Torr. The growth rate of the CeO 2 films was 200 nm/min at T=520 °C and P O 2 =2.30 Torr, which is much faster than those prepared by other physical deposition methods. The (2 0 0) texture of NiO was formed at T=450 °C and P O 2 =1.67 Torr. The full width half maximum of the both films was in the range of 8–10°. The AFM surface roughness of the films was between 3.0–10 nm, depending on the deposition temperature.

Field electron emission from CdTe deposited tungsten tip: light-induced effects

Cadmium telluride (CdTe) film has been deposited on tungsten field emitter tip by metal-organic chemical vapor deposition method. The deposited film on tungsten tip was characterized by scanning electron microscopy and energy dispersive X-ray analysis. In an all-glass field emission microscopy experiment, current–voltage characteristics were recorded after annealing the tip at ∼950 K for 30 s. Field emission current stability was recorded for 1, 3 and 5 μA current levels. While recording the stability, the field emitter was also exposed to the light (incandescent lamp, power ∼500 W) from a distance of ∼23 cm for 5 min. This resulted into enhancement in the current levels up to 40%. After switching off the lamp, current decreased to its originally set value with a finite decay time. The results are discussed in the light of existing literature and properties of CdTe and other solar energy materials.

A new system design for the preparation of copper/activated carbon catalyst by metal-organic chemical vapor deposition method

A metal-organic chemical vapor deposition (MOCVD) technique was used to prepare heterogeneous metallic catalyst supported on activated carbon. A new system design was built to achieve higher metal loading within a shorter preparation time. In the optimization of system parameters, higher metal loading can be achieved by using longer deposition time, optimum carrier gas flow rate, higher operating temperature of either evaporation zone or a deposition zone or a smaller amount of porous support. Several techniques were carried out to characterize the catalyst such as physisorption, X-ray diffraction, inductively coupled plasma—optical emission spectroscopy and scanning electronic microscopy assisted with the Energy dispersive X-ray spectroscopy (SEM-EDX). It was found that the BET specific surface area and total adsorption volume of the prepared catalysts were reduced after metal deposition, due to the formation of the deposited copper onto the porous media both externally and internally. The morphology of the cylindrical Cu/AC was analyzed by SEM-EDX. The results show that the metal was deposited with a reasonably uniform distribution onto the inner part of the porous support.

Preparation of nano-structured ceramics using nanosized Al2O3 particles

This study is established with the theory that toughness of ceramics can be improved by reducing the grain sizes of alumina (Al2O3) ceramics. For nano-structured Al2O3 ceramics, nano-sized Al2O3 particles can be synthesized by MOCVD (metal organic chemical vapor deposition) method with Al(CH3)3. The synthesized particle sizes were 5.6, 11.2 and 22.4 nm, and these particles were used as initial materials. The grain sizes in nano-structured ceramics were controlled by both sintering temperature and holding time. They transformed dramatically from γ-Al2O3 to α-Al2O3 when sintered above 1223 K for two hours. The transformation temperature was lowered by 250 K in comparison the temperature of the phase transformation in bulk. The grain size of nano-structured alumina ceramics grew with increasing sintering temperature. At the sintering temperature of 1173 K, it is necessary of an incubation time for grain growth. The incubation time became longer while particle size decreased. After the incubation time, the rate of grain growth was steeply increased. Above 1273 K, the grain growth directly occurred without any incubation time.

A Novel Iridium Precursor for MOCVD

ABSTRACTA novel liquid iridium precursor (1,3-cyclohexadiene)(ethylcyclopentadienyl)iridium, Ir(EtCp)(CHD), was synthesized and its physical properties were examined. Ir(EtCp)(CHD) exhibited enough vapor pressure (0.1 Torr/75°C), excellent volatility and adequate decomposition temperature. Characteristics of the Ir films deposited using Ir(EtCp)(CHD) and the conventional Ir precursor (1,5-cyclooctadiene)(ethylcyclopentadienyl)iridium, Ir(EtCp)(COD), by metal-organic chemical vapor deposition (MOCVD) method were compared. Ir films grown using Ir(EtCp)(CHD) showed shorter incubation time and higher nucleation density than those of films using Ir(EtCp)(COD).

Liquid Delivery Metal-Organic Chemical Vapor Deposition of Pb(ZrxTi1-x)O3 Thin Films for High-Density Ferroelectric Random Access Memory Application

The growth characteristics of Pb(ZrxTi1-x)O3 (PZT) thin films were investigated for application to high-density ferroelectric random access memories (FeRAM) devices. Films were grown by the liquid source metal-organic chemical vapor deposition (LS-MOCVD) method with tmhd-family precursors, such as Pb(tmhd)2, Zr(tmhd)2(OiPr)2 and Ti(tmhd)2(OiPr)2, dissolved in octane. Film deposition was mainly performed at 560°C, because it is the highest temperature at which bottom electrode contact could be maintained against oxidation in our capacitor over bit-line (COB) structure. The control of Pb precursor supply plays the most critical role in realizing a reliable process for PZT thin film deposition. We have monitored the changes in the microstructure and electrical properties of films on increasing the Pb precursor supply into the reaction chamber. Under optimized conditions, Ir/IrO2/PZT(100 nm)/Ir capacitor shows well-saturated hysteresis loops with a remanent polarization (Pr) of ∼ 28 µC/cm2 and coercive voltage of 0.8 V at 2.5 V.

Activation of Nitrogen Acceptor in ZnSe Homo-Epilayer Grown by MOCVD

A ZnSe epitaxial layer doped with nitrogen (N) has been grown on ZnSe substrate at optimized conditions by a low-pressure metalorganic chemical vapor deposition (MOCVD) system using hydrogen as a carrier gas and ammonia as a dopant source. In order to enhance the activation ratio of nitrogen in ZnSe epitaxial layer, ZnSe : N/ZnSe was annealed in atmosphere with zinc-saturated vapor pressure. Photoluminescence spectra measured at 4.2 K from annealed ZnSe : N epilayers showed the stronger I1N emission. C–V measurement showed that the ZnSe : N epitaxial layer is of p-type conductivity and the highest net acceptor concentration reaches as high as 6.7 × 1017 cm—3. This is the highest value for the ZnSe homosystem epitaxial layers grown by the MOCVD method at present. Furthermore, the ionization energy of nitrogen in ZnSe was estimated to be 109 meV by examining the dependence of DAP emission on the measuring temperature.

Second-Harmonic Generation of Blue Light in Epitaxial K3Li2-xNb5+xO15+2x Waveguides on K3Li2-x(Nb0.98Ta0.02)5+xO15+2x Substrates by Metalorganic Chemical Vapor Deposition

We report a new second-harmonic generation blue laser using a K3Li2-xNb5+xO15+2x single crystal film waveguide on a K3Li2-x(Nb0.98Ta0.02)5+xO15+2x crystal substrate by the metalorganic chemical vapor deposition method. Second-harmonic blue light with output power of 2 mW at 487 nm was successfully generated. The phase-matched wavelength bandwidth of the device was 1.3 nm, and the temperature coefficient of the phase-matched wavelength was 0.36 nm/°C. Crystallographic evaluation was also performed for the KLN thin film crystal. The (001) plane of KLN crystal film was well orientated to the (001) plane of the KLNT substrate, and the surface morphology of the film was very smooth. Moreover, it was revealed that an as-deposited KLN film crystal has a single domain structure.

Elaboration and characterisation of Bi 2Se 3 thin films using ditertiarybutylselenide as a precursor by MOCVD system

The growth of Bi 2Se 3 thin films by metalorganic chemical vapour deposition (MOCVD) using trimethylbismuth and a novel Se-precursor: ditertiarybutylselenide (DTBSe) as bismuth and selenium sources, respectively, is investigated on pyrex substrates. These films always displayed n-type conduction for a VI/V ratio between 3 and 15. By X-ray diffraction and SEM observation, we noticed the polycrystalline structure of the layers of typical preferential c-orientation and confirmed the hexagonal structure. The microprobe data indicate that the best stoichiometry of Bi 2Se 3 was achieved. The Seebeck coefficient and the carrier concentration vary slowly with VI/V ratio: −130 to −159.2 μV/K and 2.35×10 19 to 6.15×10 19 cm −3, respectively. In contrast, the mobility and the resistivity highly depend on the VI/V ratio. Their values vary from 62 to 225 cm 2/V s and from 9.74 to 17 μΩ m, respectively. These initial results suggest a significant potential for the MOCVD method to produce good thermoelectrical materials using DTBSe as Se-precursor.

Impact of metal–oxide gate dielectric on minority carrier lifetime in silicon

Using a deposition followed by high-temperature drive in, we have examined the impact of metalorganic chemical vapor deposition (MOCVD) HfO2, MOCVD ZrO2, and physical vapor deposition (PVD) ZrxSi1−xO2 gate dielectrics on the minority carrier lifetime. The lifetime measurement utilized electrolytical metal tracer (ELYMAT)™. The minority carrier lifetime in Si after a 1025 °C anneal is comparable for HfO2 and the SiO2 control. The ELYMAT™ data showed similar results for the MOCVD ZrO2. However, a highly reduced lifetime was measured for the PVD ZrxSi1−xO2 films due to the presence of significant levels of Fe and Ni in the PVD Zr-silicate wafers as detected by VPD-TXRF. Thus, we saw no impact on minority carrier lifetime in Si for the HfO2 and ZrO2 formed by MOCVD methods, while there was a major impact on minority carrier lifetime in Si for the ZrxSi1−xO2 produced by the PVD method.

Effects of Si ion implantation and post-annealing on yellow luminescence from GaN

We have studied the effects of Si ion implantation and post-annealing on yellow luminescence (YL) from GaN. Two types of GaN samples grown by the metal-organic chemical vapor deposition method and labeled as GaN1 and GaN2 were studied. The PL spectrum of the as-grown GaN1 sample was dominated by a strong YL and that of the as-grown GaN2 sample was almost free from YL. After Si ion implantation with doses of both 1.3×10 13 and 1.0×10 16 cm −2, the intensity ratios of YL to near band edge (NBE) emission ( I Y/ I NBE) for the GaN1 samples decreased markedly compared with those of the corresponding unimplanted ones both before and after post-annealing at temperatures up to 950°C. However, for the Si-ion-implanted GaN2 sample with a dose of 1.3×10 13 cm −2, I Y/ I NBE increased compared with that of the as-grown one both before and after post-annealing. Besides, the I Y/ I NBE for Si-ion-implanted GaN1 with a dose of 1.3×10 13 cm −2 increased monotonically with annealing temperature. Our results show that only the Si ion implantation being accompanied with high-temperature post-annealing could produce YL. The possible reasons for the marked reduction in I Y/ I NBE for the GaN1 sample after Si-ion-implantation have been discussed.

Photoluminescence dependence on heterointerface for metalorganic chemical vapor deposition grown GaInNAs/GaAs quantum wells

We investigate the effect of the sequence of gas flows at heterointerfaces on optical quality of GaInNAs/GaAs quantum wells grown by metalorganic chemical vapor deposition (MOCVD). We point out that the degradation mechanism of photoluminescence of GaInNAs grown by MOCVD method is categorized in two types. One is the formation of a GaNAs layer at the heterointerface which causes both increase of emission wavelength and degradation of crystal quality. The other is generation of nonradiative centers induced by incorporation of nitrogen (N). The insertion of a GaInAs layer to the GaInNAs/GaAs heterointerface is proposed to overcome these degradation mechanisms. A GaInAs intermediate layer is effective to suppress the GaNAs formation and to reduce the total GaInNAs thickness.

Hollow fibers for delivery of harmonic pulses of Q-switched Nd:YAG lasers.

Flexible hollow fibers for delivery of the second, third, and fourth harmonic pulses of Q-switched Nd:YAG lasers are introduced. For the doubled (532-nm) wavelength, we fabricated a hollow fiber with an internal metal and polymer film by using a silver-mirror plating and a liquid-phase-coating method. For tripled (355-nm) and quadrupled (266-nm) Nd:YAG in the ultraviolet region, we fabricated aluminum hollow fibers with or without an internal polymer layer by using the metal-organic chemical-vapor deposition method. Both types of fiber show high stability for the transmission of high-peak power laser pulses with low transmission losses.

Study of GaN-based Laser Diodes in Near Ultraviolet Region

Ultraviolet (UV) laser diodes (LDs) were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We fabricated three types of UV LDs whose active layers were (I) ternary InGaN, (II) quaternary AlInGaN and (III) binary GaN single quantum well (SQW) structures. We investigated the LD characteristics in detail in the near UV region. LDs whose active layers were quaternary Al0.03In0.02Ga0.95N were demonstrated under the pulsed-current-biased conditions at room temperature. The emission wavelength of these LDs was the shortest wavelength (366.4 nm) in our experiments. We also demonstrated binary GaN SQW LDs for the first time. The threshold current density, voltage and emission wavelength of these LDs under 25°C continuous-wave (cw) operation were 3.5 kA/cm2, 4.6 V and 369.0 nm, respectively. The estimated lifetime was approximately 2000 h under 25°C cw operation at an output power of 2 mW.

Optical Properties and Dependence of Optical Transmittance on the Particle Sizes of Nano-Structured Translucent .GAMMA.-Al2O3 Ceramics.

Nano-size γ-Al2O3 particles of four different sizes were synthesized by MOCVD (Metal Organic Chemical Vapor Deposition) method and then translucent nano-structured γ-Al2O3 ceramics are pelletized under a pressure of 2.5 GPa by a uniaxial compaction-method. Although these nano-structured γ-Al2O3 ceramics showed low density, they were fairly translucent. The relationship between transmittance and thickness of these specimens can be described by Lambert-Beer's law. The nano-structured γ-Al2O3 ceramics with different particle diameter and thickness have been prepared in order to clarify the dependence of particle size on the optical transmittance. The optical transmittance decreased with increasing initial particle diameter. In the case of 0.20mm thickness samples, the γ-Al2O3 with 5.6nm initial particle diameter showed an optical transmittance of about 60%. However, the optical transmittance decreases less than 5% when initial particle diameter is increased to 34.4nm. This phenomenon could be explained by Rayleigh scattering, which is the scattering due to the particle diameter being much smaller than the wavelength of light. In these visible regions (500-800nm), a scattering coefficient related with Rayleigh scattering was inversely related to the fourth power of the wavelength and directly proportional to the square of the grain size.

Tunable barium strontium titanate thin film capacitors for RF and microwave applications

The measurement results for thin film barium strontium titanate (BST) based voltage tunable capacitors intended for RF applications are reported. At 9 V DC, BST capacitors fabricated using MOCVD (metalorganic chemical vapor deposition) method achieved 71% (3.4:1) tunability. The measured device quality factor (Q) for BST varactors is comparable with the device Q for commercially available varactor diodes of similar capacitance. The typical dielectric loss tangent was in the range 0.003-0.009 at VHF. Large signal measurement and modeling results for BST thin film capacitors are also presented.