Organic Chemical Vapor Deposition Method Research Articles

Origin of p-type conductivity for N-doped ZnO nanostructure synthesized by MOCVD method

Undoped and nitrogen-doped ZnO nanostructures were grown by Metal Organic Chemical Vapor Deposition method onto Sapphire substrates using NH3 gas as N source. Structural and optical characterizations of undoped and N-doped ZnO nanostructures were done. The XRD studies show that a few peaks arose and the relative intensities of other peaks [in comparison to (002)] increase with higher incorporation of N. PL studies revealed that the width and intensity of PL peaks are strongly influenced by NH3 concentration during growth, which creates a few donor levels (arising due to structural defects) as well as acceptor levels (arising due to N doping). With increase of NH3 concentration during deposition, O substitution by N increases and more NO defects appear in PL spectrum. The effect of oxygen vacancies was compensated by the effect of defect levels appears due to N doping, which causes the p-type nature of N-doped ZnO. The p-type nature of the N-doped ZnO nanostructures was also confirmed by using Hall-effect measurement.

(Invited) Challenges of Energy Band Engineering with New Sn-Related Group IV Semiconductor Materials for Future Integrated Circuits

Research and development of GeSn and related group-IV semiconductor materials have been widely extended in recent years for not only electronic transistors but also various optoelectronic applications [1,2]. Design and engineering of the energy band structure of group-IV semiconductor materials are swiftly blossoming with establishing the crystal growth technology of GeSn and related materials. We have successively developed the crystalline growth technology of GeSn and GeSiSn thin films on various substrates mainly by using molecular beam epitaxy [1-7]. Recently, we also achieved the epitaxial growth of GeSn layer by using metal organic chemical vapor deposition method [8]. In this presentation, we will report our recent achievements of our study for the crystalline growth and electronic properties including energy band structure of GeSn and related group-IV materials. Controlling the composition of elements and the strain structure of the group-IV semiconductor alloys promises prospective energy band engineering technology. Increasing in the Sn content over about 10% or tensile strain over about 1% achieve the indirect-to-direct crossover, which is a strong driving force of the optical applications of GeSn material. In addition, we recently achieved the formation of polycrystalline SiSn thin layers with a very high Sn content of 20%, and demonstrated that the direct bandgap decreases to 1.05 eV with Si-Sn alloying, which is just 0.22 eV higher than the indirect bandgap of the poly-SiSn even by using Si matrix material [9]. Also, the ternary alloy GeSiSn promises the control of the energy band structure independently on the lattice constant by changing each content of three elements. We found that unstrained GeSiSn/Ge heterostructure realizes a type-I energy band alignment without using strain structure, that promises various electronic and optoelectronic applications [10]. We will demonstrate the experimental results of the energy band engineering with GeSn and related materials. The energy band engineering also provides controlling technology of the electronic property at the interface such as metal/Ge contact. Recently, we found that the Sn/Ge or GeSn/Ge contacts effectively reduces the Schottky barrier height at the metal/n-Ge interface [11,12]. In our presentation, we will also discuss the influence of the energy band structure on the interface properties for Ge and GeSn. This work was partially supported by Grant-in-Aid for Scientific Researches of the JSPS and the JSPS Core-to-Core Program, A. Advanced Research Networks.

Ternary Al2xIn2−2xO3 films with tunable optical band gap prepared on YSZ (1 0 0) substrates by metal organic chemical vapor deposition

The ternary Al2xIn2−2xO3 films with different Al contents of x [Al/(Al+In) atomic ratio] have been fabricated on the Y-stabilized ZrO2 (YSZ) (100) substrates by the metal organic chemical vapor deposition (MOCVD) method at 700°C. The influence of various Al contents (x=0.1–0.9) on the structural, electrical and optical properties of the films have been investigated. Structural analyses revealed a phase transition from the bixbyite In2O3 structure with a single orientation along (100) to the amorphous structure as the Al content increases from 10% to 90%. The lowest resistivity of 4.84×10−3Ωcm with a carrier concentration of 1.1×1020cm−3 and a Hall mobility of 11.74cm2V−1s−1 were obtained for the sample with x=0.2. The average transmittances for the Al2xIn2−2xO3 films in the visible range were all over 77% and the optical band gap of the films could be modulated from 3.67 to 4.73eV.

Preparation and characterization of Al2xIn2−2xO3 films deposited on MgO (1 0 0) by MOCVD

The ternary Al2xIn2−2xO3 films with different compositions x[Al/(Al+In) atomic ratio] have been fabricated on the MgO (100) substrates by the metal organic chemical vapor deposition (MOCVD) method. The influence of different Al contents on the structural, optical and electrical properties of Al2xIn2−2xO3 films has been studied. The structural studies reveal a change from single crystalline structure of cubic In2O3 to amorphous as the Al content increases. The average transmittances of all samples in the visible range are over 80%. The optical band gap is observed to increase monotonically from 3.67 to 5.38eV as the Al content increases from 0.1 to 0.9.

High-power passively mode-locked Nd:YVO(4) laser using SWCNT saturable absorber fabricated by dip coating method.

Passive mode locked laser is typically achieved by the Semiconductor Saturable absorber Mirror, SESAM, saturable absorber, which is produced by expensive and complicated metal organic chemical vapor deposition method. Carbon based single wall carbon nanotube (SWCNT), saturable absorber, is a promising material which is capable to produce stable passive mode-locking in the high power laser cavity over a wide operational wavelength range. This study has successfully demonstrated the high power mode locking laser system operating at 1 micron by using SWCNT based absorbers fabricated by dip coating method. The proposed fabrication method is practical, simple and cost effective for fabricating SWCNT saturable absorber. The demonstrated high power Nd:YVO(4) mode-locked laser operating at 1064nm have maximum output power up to 2.7W,with the 167MHz repetition rate and 3.1 ps pulse duration, respectively. The calculated output pulse energy and peak power are 16.1nJ and 5.2kW, respectively.

Preparation and characterization of Sn-doped β-Ga2O3 homoepitaxial films by MOCVD

Sn-doped gallium oxide (Ga2O3:Sn) films were deposited on β-Ga2O3 (100) substrates by metal organic chemical vapor deposition method. The Sn concentration was varied from 1 to 12 % (atomic ratio). The influences of Sn-doping concentration on structure, raman, and photoelectric properties of the films were investigated in detail. The obtained films were monoclinic β-Ga2O3 homoepitaxial films. A decrease of about eight orders of magnitude in the film resistivity could be achieved through Sn doping. The 10 % Sn-doped film exhibited the best electrical properties and the lowest resistivity of about 1.20 × 10−1 Ω cm, with the hall mobility value of 12.03 cm2 V−1 s−1obtained. The average transmittances of the β-Ga2O3: Sn films in the visible and UV wavelength ranges were all over 85 %. The optical band gap of the films with different Sn-doping concentrations could be modulated from 4.16 to 4.69 eV.

Photo-catalytic destruction of ethylene using microwave discharge electrodeless lamp

A double tube type microwave discharge electrodeless lamp was employed to investigate the photo-catalytic decomposition of ethylene gas, an important VOC species. The anatase TiO2 film photo-catalyst balls prepared by a low pressure metal organic chemical vapor deposition method were used. In addition, the advantages of microwave/UV/TiO2 photo-catalysts hybrid process were analyzed. The removal performance was examined under different conditions with different initial ethylene concentrations, gas residence times and oxygen concentrations. At all microwave powers tested, UV-C exhibited much larger irradiance than UV-A and UV-B. The degradation efficiency of ethylene increased with increasing microwave intensity, with decreasing inlet concentration, and with decreasing reaction gas flow rate. Taking the energy cost into account, residence time should be determined considering inlet concentration, volume of degradation, capacity of devices, and admitted costs. Microwave intensity was shown to be a critical operation variable for the photo-catalytic degradation of ethylene, required to be determined depending on initial ethylene concentration.

A novel MOCVD reactor for growth of high-quality GaN-related LED layers

Gallium nitride (GaN), a direct bandgap semiconductor widely used in bright light-emitting diodes (LEDs), is mostly grown by metal–organic chemical vapor deposition (MOCVD) method. A good reactor design is critical for the production of high-quality GaN thin films. In this paper, we presented a novel buffered distributed spray (BDS) MOCVD reactor with vertical gas sprayers and horizontal gas inlets. Experiments based on a 36×2″ BDS reactor were conducted to examine influence of the process parameters, such as the operating pressure and the gas flow rate, on the growth efficiency and on the layer thickness uniformity. Transmission electron microscopy (TEM) and photoluminescence (PL) are further conducted to evaluate quality of the epitaxial layers and to check performance of the reactor. Results show that the proposed novel reactor is of high performance in growing high-quality thin films, including InGaN/GaN multiquantum wells (MQWs) structures.

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.

Structural and optical properties of Al2xIn2−2xO3films prepared by metal-organic chemical vapor deposition

Tunable band gap Al2xIn2−2xO3 films with different compositions x[Al/(Al + In) atomic ratio] were grown on MgO (110) substrates by the metal organic chemical vapor deposition (MOCVD) method at a temperature of 700 °C. The effects of different Al concentrations on the structural and optical properties of the obtained films were discussed in detail. The film deposited with an Al concentration of x = 0.1 showed single crystalline bixbyite In2O3 structure with Al0.2In1.8O3 (110)‖MgO (110), while the films with x = 0.3 and 0.5 had polycrystalline structures, and the sample prepared with x = 0.9 exhibited γ-Al2O3 structure. The transmittances of all the samples exceeded 80% in the visible region. The optical absorption edges of the films shifted to short wavelength, and the bandgap of the prepared films could be monotonously modulated from 3.73 eV to 5.82 eV as the Al concentration increased from 0.1 to 0.9.

Coating of spinel LiNi0.5Mn1.5O4 cathodes with SnO2 by an electron cyclotron resonance metal–organic chemical vapor deposition method for high-voltage applications in lithium ion batteries

Tin oxide coating by employing electron cyclotron resonance metal–organic chemical vapor deposition was performed on 5V-class spinel LiNi0.5Mn1.5O4 cathode electrodes prepared by a conventional tape-casting method. The pristine and SnO2-deposited LiNi0.5Mn1.5O4 electrodes were characterized by X-ray diffraction, field-emission electron probe microanalyzer, field-emission scanning electron microscopy, Auger electron spectroscopy, charge–discharge measurements, and electrochemical impedance spectroscopy were evaluated in lithium cells using the fabricated electrodes. The SnO2-deposited LiNi0.5Mn1.5O4 electrodes exhibited better rate capability at room temperature and superior electrochemical performance during the storage test evaluated at 60°C in a fully charged state than the pristine LiNi0.5Mn1.5O4 electrode. Also, surface modification of the LiNi0.5Mn1.5O4 electrode was found by impedance analyses to be effective for suppressing the increase of the charge transfer resistance during the storage test at elevated temperatures.

A Study on the Electrical Properties of Gan-Based Alpha Particle Detector

Pin structure GaN-based alpha particle detector with epitaxial growth on c-plane sapphire substrate through metal organic chemical vapor deposition (MOCVD) method, uses electron beam evaporation and photoetching machine to produce the ohmic contact electrodes of device. The electrical properties of device which were tested by I-V and C-V show that the device’s reverse leakage current is 9.9μA at 100V reverse bias voltage is at; and the detector’s junction capacitance is 19pF at 20V reverse bias voltage.

Studies on dislocation and surface morphology of AlxGa1−xN/GaN heterostructures grown by MOCVD

In this work, AlxGa1−xN epilayers have been grown on sapphire substrate with GaN template by the metal organic chemical vapor deposition (MOCVD) method. The structural and morphological properties of these samples have been investigated and compared. The growth rate of AlGaN has been found to decrease with increasing Al composition. By increasing Al composition of AlGaN epilayer, tilt and twist angle has been found to increase, indicating higher threading dislocation density. Surface morphology and dislocation density (DD) have been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different types of dislocation etch pits have been observed in AlxGa1−xN/GaN epilayers, using orthophosphoric acid (85% H3PO4) as defect selective etchant. Three types of etch pits like screw type (α), edge type (β) and mixed type (α+β) dislocations have been observed. The mechanism of etch pits formation has been explained using Cabrera’s thermodynamic model. The etch pit density (EPDs) has been correlated with threading dislocation density (TDs) estimated using HRXRD measurements. Photoluminescence (PL) studies have revealed an increase in intensity of near band edge emission due to etching.

Characterization of homoepitaxial β-Ga2O3 films prepared by metal–organic chemical vapor deposition

β-Ga2O3 films have been homoepitaxially deposited on β-Ga2O3 (100) substrates by metal organic chemical vapor deposition (MOCVD) method. The influences of different growth temperatures on the structure, Raman and optical properties of the homoepitaxial films have been studied. The structure of the obtained films is monoclinic β phase gallium oxide and the film deposited at 650°C exhibits the best crystalline quality. The average transmittance of the samples in the visible and UV wavelength range is about 80%. The optical band gap of the films deposited at 600, 650 and 700°C are about 4.72, 4.73 and 4.68eV, respectively.

High power 940 nm quantum well laser with asymmetric structure

In order to improve the performance of the general broad area high power 940 nm InGaAs/GaAs semiconductor laser diode (LD), we design a new type quantum well LD with an asymmetric waveguide and cladding structure. High material quality with low internal loss of 0.44 mm-1 has been achieved using low pressure metal organic chemical vapor deposition (LP-MOCVD) method. Broad-area lasers were fabricated with the wafers grown on GaAs substrates. For the 940 nm devices with 100 m-wide stripe and 2000 m-long cavity under 25 ℃ continuous wave (CW) operation condition of 10 A, the typical threshold current is 251 mA, the slope efficiency is 1.22 W/A , and the maximum output power reaches 9.6 W. The laser diode yielded a maximum power conversion efficiency over 70%.

Synthesis, Surface Characterization and Photocatalytic Activity of TiO2 Supported on Almond Shell Activated Carbon

Three types of photocatalysts were synthesized by metal organic chemical vapor deposition and impregnation methods using the almond shell activated carbon as support. These photocatalysts denoted by (TiO2/ASAC (V), TiO2/ASAC (I1) and TiO2/ASAC (I2)) were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and nitrogen adsorption–desorption isotherms. SEM observation shows that TiO2 was deposited on activated carbon surface. XRD results confirm that TiO2 existed in a mixture of anatase and rutile phases. The DRS spectra show the characteristic absorption edge of TiO2 at approximate 380 nm corresponding to the optical band gap of 3.26 eV. Besides, FTIR spectrum indicated the presence of (Ti–O) groups. The specific surface area of photocatalysts decreased drastically in comparison with the original activated carbon. The catalysts were very efficient for the photodegradation of total organic carbon (TOC) from industrial phosphoric acid solution under UV irradiation. The kinetics of photocatalytic TOC degradation was found to follow a pseudo-first-order model. The prepared TiO2/ASAC showed high photoactivity for the photodegradation of TOC in the following order: TiO2/ASAC (V) > TiO2/ASAC (I1) > TiO2/ASAC (I2) > ASAC > TiO2 (P25).

Nano sized bismuth oxy chloride by metal organic chemical vapour deposition

Metal organic chemical vapour deposition (MOCVD) method was used to prepare thin films of bismuth based nano particles starting from bismuth salts. Nano sized bismuth oxy chloride (BiOCl) crystals were synthesized from solution containing bismuth chloride (BiCl3) in acetone (CH3COCH3). Self-assembly of nano sized BiOCl crystals were observed on the surface of silicon, fused silica, copper, carbon nanotubes and aluminium substrates. Various synthesis parameters and their significant impact onto the formation of self-assembled nano-crystalline BiOCl were investigated. BiOCl nano particles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Micro-Raman spectroscopy. These analyses confirm that bismuth nanometer-sized crystal structures showing a single tetragonal phase were indeed bismuth oxy chloride (BiOCl) square platelets 18–250nm thick and a few micrometres wide.

Mechanical properties of individual InAs nanowires studied by tensile tests

Mechanical properties of individual InAs nanowires (NWs) synthesized by metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) methods are studied by in-situ tensile tests in a scanning electron microscope and their fracture strength and Young's modulus are obtained. The two types of NWs both exhibit brittle fracture with a maximum elastic strain up to ∼10%. Their fracture strength distributes in a similar range of ∼2–5 GPa with a general trend of increasing with NW volume decrease, which is well described by Weibull statistic with a smaller Weibull modulus and a higher characteristic strength for MOCVD NWs. Young's modulus is determined to be 16–78 GPa with an average value of 45 GPa and no dependence on NW diameter for MOCVD NWs and 34–79 GPa with an average value of 58 GPa for MBE NWs.

Room temperature ferromagnetism in Cd-doped ZnO thin films through defect engineering

Room-temperature ferromagnetism is detected in undoped and cadmium-doped ZnO (ZnO:Cd) thin film grown on c-plane sapphire substrate by metal–organic chemical vapor deposition method. To elucidate the origin of ferromagnetism, a theoretical study based on density functional theory is conducted, focusing on the role of the neutral cation vacancy on the appearance of magnetism in Cd-doped ZnO thin film. The calculations revealed that Cd substitution at Zn sites contributes to the long-ranged ferromagnetism in ZnO by lowering the formation energy of Zn vacancies and thereby stabilizing Zn vacancies from which the magnetic moments originate.

Study of boron-doped zinc oxide film serving as front contact with high haze used in amorphous silicon thin film solar cells

Boron-doped zinc oxide (BZO) deposited by metal organic chemical vapor deposition (MOCVD) method is used as front contact in amorphous silicon thin film solar cells. Asahi-U type SnO2:F is used as the reference front contact for comparison. When the a-Si:H intrinsic layer thickness is changing changed, the performance of a-Si:H solar cells shows different evolution trends. These different results can be understood from the shadowing effect during the growth of intrinsic silicon material, which is caused by the as-grown pyramid texture in the surface of BZO substrate. In order to reduce this negative effect on the performance of solar cells, the deposition temperature of the a-Si:H intrinsic layer is optimized, to thereby improving improve the open circuit voltage and fill factor. The conversion efficiency of a-Si:H solar cells can reach up to 7.34%, with the thickness of absorber layer being only around 200 nm. and only Al back reflector is being used.