Organic Chemical Vapor Deposition Method Research Articles

Two-step growth of β-Ga2O3 on c-plane sapphire using MOCVD for solar-blind photodetector

In this work, a two-step metal organic chemical vapor deposition (MOCVD) method was applied for growing β-Ga2O3 film on c-plane sapphire. Optimized buffer layer growth temperature (T B) was found at 700 °C and the β-Ga2O3 film with full width at half maximum (FWHM) of 0.66° was achieved. A metal−semiconductor−metal (MSM) solar-blind photodetector (PD) was fabricated based on the β-Ga2O3 film. Ultrahigh responsivity of 1422 A/W @ 254 nm and photo-to-dark current ratio (PDCR) of 106 at 10 V bias were obtained. The detectivity of 2.5 × 1015 Jones proved that the photodetector has outstanding performance in detecting weak signals. Moreover, the photodetector exhibited superior wavelength selectivity with rejection ratio (R 250 nm/R 400 nm) of 105. These results indicate that the two-step method is a promising approach for preparation of high-quality β-Ga2O3 films for high-performance solar-blind photodetectors.

A study on the dark and illuminated operation of Al/Si3N4/p-Si Schottky photodiodes: optoelectronic insights

This work extensively investigates the operation of an Al/ Si3N4/p-Si Schottky-type photodiode under dark and varying illumination intensities. The photodiode is fabricated by employing the metal–organic chemical vapor deposition (MOCVD) method. A thorough electrical characterization is performed at room temperature, encompassing measurements of current–voltage (I–V), current–time (I–t), capacitance–time (C–t), and conductance time (G–t). The photodiode’s rectification factor and reverse bias area increased under illumination. The relationship between light power density, barrier height, and diode ideality factor is found. The study also found a strong correlation between light intensity and applied voltage on series resistance (Rs) and shunt resistance (Rsh). Rs values are calculated using Cheung’s functions, revealing the diode’s resistance behavior. The study also examines the photodiode’s photoconductivity and photoconductance, finding a non-linear relationship between photocurrent and illumination intensity, suggesting bimolecular recombination. Calculated photosensitivity (K), responsivity (R), and detectivity (D*) values show the device’s light response effectiveness, but efficiency decreases at higher illumination intensities. Transient experiments indicate stable and reproducible photocurrent characteristics, revealing photogenerated charge temporal evolution. This study provides a complete understanding of the Al/Si3N4/p-Si Schottky photodiode’s behavior under different illumination intensities. The findings advance optoelectronic device knowledge and enable their use in advanced technologies.

Large-area epitaxial growth of InAs nanowires and thin films on hexagonal boron nitride by metal organic chemical vapor deposition

Large-area epitaxial growth of III–V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1 109 cm−2 is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm−2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III–V thin films on van der Waals substrates.

First-principles study on the effects of different valence VZn and Ag doping with Hi co-existence on the magnetism and photocatalysis of ZnO

In vacuum environment, metal organic chemical vapor deposition (MOCVD) method was used in experiments, with Ag doping and cation vacancy (VZn) doping in ZnO, where unintentional Hi cannot be avoided. However, studies on the effect of H interstitial physical properties are few. In this study, first-principles generalized gradient approximation plane-wave ultra-soft pseudopotential GGA + U approach within the frame of DFT is used to study the influences of VZn and Ag doping in different valencies with Hi on the magnetism and photocatalysis of ZnO.Under O-rich conditions, Zn34Ag2+HiO36(VZn0) has the best thermodynamic stability. Researches showed that Zn34Ag1+O36(VZn0) has a 2 μB magnetic moment, and magnetism is mainly generated by the roving electrons (O−) using the VZn as medium. Photocatalysis increases with the increase of Ag valence state. Especially, Zn34Ag2+HiO36(VZn0) has a relatively long electronic lifetime of 5.35 × 10−12 s, the strongest visible light absorption ability, relatively high carrier activity and relatively strong reduction ability.

An electrochemical sensor based on rGO/GaN nanowires for Pb(II) determination

In this work, rGO/GaN nanowires electrochemical sensors were fabricated on sapphire substrates by metal organic chemical vapor deposition (MOCVD) and electrodeposition method, and it was used for the detection of Pb2+ in water. Reduced graphene oxide (rGO) increases the specific surface area and active sites of gallium nitride nanowires (GaN NW), and GaN NW improves the stability of the rGO, thus a highly sensitive electrochemical sensor was established. Square wave anodic stripping voltammetry (SWASV) was used to detect Pb2+. Effects of experimental conditions such as rGO modification amount, pH, Pb2+ deposition potential/time on the detection performance were investigated. With optimized detection conditions, the rGO/GaN NW sensor features high sensitivity (0.7362 μA μg-1 L) in the linear range of 2.5-200 μg L-1, and the detection limit was 2.5 μg L-1. Furthermore, the rGO/GaN NW sensor exhibited a good stability and repeatability.

High-Performance Flexible GaAs Nanofilm UV Photodetectors

Flexible ultraviolet (UV) photodetectors have attracted extensive research interest due to their potential applications in personal UV monitoring, UV electronic eye, anti-UV gloves, and other wearable systems. In this study, we present a highly sensitive flexible UV photodetector based on an ultrathin GaAs layer that is produced using a metal–organic chemical vapor deposition method and epitaxial lift-off film transfer technology. Device performance analysis reveals that the photodetectors made of a 50 nm thick GaAs layer have excellent sensitivity to 365 nm light. Specifically, the responsivity, specific detectivity, and external quantum efficiency could reach as high as 99.01 A W–1, 1.51 × 1012 Jones, and 3.37 × 104%, respectively, at −2 V bias voltage, which are comparable to many UV photodetectors made from conventional wide band gap semiconductors. Such outstanding UV response properties are related to the very high absorption coefficient for UV light and carrier mobility of an ultrathin GaAs film. Equally importantly, the mechanical flexibility resulting from reducing the film thickness allows the device to maintain its photoelectric properties even after more than 500 bending cycles. The totality of these results suggests that our flexible UV photodetectors have strong potential applications in future wearable devices.

A first-principles study on the effect of point defects on the magnetism of the AlN:Li/Na/K system

When AIN semiconductors are grown by metal–organic chemical vapor deposition and vacuum-coating methods, interstitial H atoms are unintentionally incorporated into AlN and are often overlooked. To solve this problem, the present study adopted the first-principles hybrid functional HSE06 method under the framework of density functional theory to examine the impact of the point defects (VAl and Hi) on the magnetic properties of the AlN:Li/Na/K system. Results showed that all doped systems had single-ion spin-polarized N2− at different positions to generate magnetism, different from the source of magnetic coupling in conventional doped systems. Compared with the Al34MN36 (M = Li/Na) and Al34N36 systems, the magnetic moments of the Al34MHiN36 (M = Li/Na) and Al34HiN36 systems increased after incorporating the interstitial H. Moreover, the Al34MHiN36 (M = Li/Na) and Al34HiN36 systems unpaired itinerant electrons, and the magnetism was generated mostly by the unpaired itinerant electrons of N2− ions. The itinerant electrons exchanged electrons through Al vacancies to generate magnetism. Furthermore, the total magnetic moment of the Al34KHiN36 and Al35HiN36 systems were zero, and the use of interstitial H regulation as magnetic switches was very advantageous for these systems.

Luminescent iron disilicide film growth by metal–organic chemical vapor deposition

Semiconducting iron disilicide (β-FeSi2) films were epitaxially grown on the Ag-layer pre-coated Si(111) substrates with an initial β-FeSi2 layer by the metal–organic chemical vapor deposition method. These β-FeSi2 films had (101)-preferred orientations, and their crystal quality was improved as the growth temperature increased from 893 to 1093 K. The photoluminescence (PL) intensity of the (101)-oriented β-FeSi2 films grown at 973 K was larger than those of β-FeSi2 films at the other deposition temperatures, which indicates the decrease of the density of nonradiative recombination centers in β-FeSi2. A clear A-band emission originated from β-FeSi2 was observed for these films up to 285 K. This pronounced PL intensity enhancement from β-FeSi2 is attributed not only to the crystallinity evaluated by XRD measurement but also to the decrease in density of thermal equilibrium Si vacancy in β-FeSi2.

Conformal Growth of Hexagonal Boron Nitride on High-Aspect-Ratio Silicon-Based Nanotrenches

We successfully accomplished the conformal growth of sp2-hybridized few-layer h-BN over an array of Si-based nanotrenches with a 45 nm pitch and an aspect ratio of ∼7:1 by using the pulsed-mode metal–organic chemical vapor deposition (MOCVD) method. Surface-sensitive X-ray absorption fine structure spectroscopy and density functional theory calculations revealed that the B–O bonds formed on the noncatalytic SiO2 surface act as nucleation sites for the subsequential formation of mixed sp2- and sp3-hybridized BON2 and BN3 at the very initial stage of the pulsed-mode injection of MOCVD precursors, enabling the conformal growth of few-layer sp2-hybridized h-BN with an excellent step coverage. We believe that these results can provide a broad avenue for the implementation of fascinating two-dimensional layered materials for current state-of-the-art three-dimensional Si-based nanoscale architectures, overcoming the downscaling limits.

Enhanced catalytic performance of CuCr/ZSM-5 catalyst by chemical vapour deposition for trichloroethylene oxidation

ABSTRACT The CuCr mixed oxides catalysts supported on ZSM-5 zeolite (CuCr/ZSM-5) were synthesized via metal organic chemical vapour deposition (MOCVD) method for catalytic oxidation of trichloroethylene (TCE). SEM, XRD, BET, H2-TPR, NH3-TPD and XPS were tested. The active components were dispersed uniformly over the surface of ZSM-5 zeolite. The catalytic experimental results exhibited that the CuCr/ZSM-5 exhibited the best catalytic performance for TCE oxidation with 90% of TCE at 338°C and the concentration of C2Cl4 decreased compared with Cu/ZSM-5 and Cr/ZSM-5. The possible reason is that CuCr/ZSM-5 has superior reducibility, higher Cu2+ surface concentration as well as more surface oxygen.

Effect of different valence cation vacancies and interstitial H on the photocatalytic performance of two-dimensional GaN:(O/C)

The effects of point defects on the physical properties of gallium nitride (GaN) monolayer surfaces have been widely reported in experimental and theoretical computational studies. However, the effects of different valence states of VGa and O/C and interstitial H co-doping on the photocatalytic properties of two-dimensional (2D) GaN surfaces have been rarely reported. Experimental studies on GaN based on Metal Organic Chemical Vapor Deposition and Vacuum Coating methods often overlook the unintentional existence of interstitial H in Ga vacancy. The structure, stability, and main affecting factors of the photocatalytic performance of Ga35MHiN35 (VGa3−/VGa2−/VGa1−/VGa0) (M = O/C) 2D surfaces were investigated to solve the present problem by using a generalized gradient approximation of the plane wave supersoft pseudopotential + U in the framework of density generalization theory. Results show that the 2D surface of Ga35MHiN35(VGa3−/VGa2−/VGa1−/VGa0) (M = O/C) is more stable under N-rich conditions, and the surface is more easily doped. Analysis of the electric dipole moment, effective mass, optical properties, and redox reactions of the doped surfaces reveals that the 2D surface of Ga35CHiN35 (VGa3−) has the best carrier activity, the best absorption spectral redshift, the longest carrier lifetime, and the strongest redox ability. Therefore, the 2D surface of Ga35CHiN35(VGa3−) is best as a photocatalyst. This work facilitates the preparation of new 2D GaN photocatalysts.

Ultrasensitive UV-C detection based on MOCVD-grown highly crystalline ultrawide bandgap orthorhombic κ-Ga2O3

Orthorhombic κ-Ga2O3, as one of the Ga2O3 polymorphs, is considered a promising as ultrawide bandgap material for extreme environment devices. It is considered more superior than the conventional group III-V compound semiconductors and silicon carbides in extreme environments demanding material/device characteristics of high-voltage, high-temperature, high-pressure, high-impact, and high-radiation. In this study, we demonstrate ultrasensitive ultraviolet-C (UV-C) detection using Si-doped orthorhombic κ-Ga2O3 photodetectors. A 150 nm thick κ-Ga2O3 film was grown on a 2-inch diameter sapphire (α–Al2O3) wafer via metal organic chemical vapor deposition (MOCVD) method. The crystallinity of orthorhombic κ-Ga2O3 film was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ultrawide bandgap of approximately 4.9 eV was confirmed by UV transmittance measurement. For UV-C detection analysis, a planar device with a channel length of 20 μm was fabricated using Au/Ti metal contacts on the orthorhombic κ-Ga2O3 film. The device doped under 15 sccm SiH4 flow rate showed ultrahigh photoresponse of ∼72.1 A/W, Ion/Ioff of ∼14, and decent rise (∼0.35 s) and decay (∼1.79 s). Our results will contribute to the understanding on a new material phase of κ-Ga2O3, as well as on developing optoelectronics devices with high radiation hardness suitable for operation in extreme environments.

Determination of type-ΙΙ band alignment β-Ga2O3/GaAs heterojunction interface by x-ray photoelectron spectroscopy

A high-quality β-Ga2O3 film was grown on a (111) GaAs substrate using the metal organic chemical vapor deposition method. The band alignment of the β-Ga2O3/GaAs heterojunction interface was determined by x-ray photoelectron spectroscopy. The energy-band structure of β-Ga2O3/GaAs was constructed based on the binding energies of Ga 3d and As 3d core levels as well as valence band maximum values. The valence band offset was determined to be 3.50 ± 0.05 eV. As a consequence, a type-ΙΙ heterojunction with a conduction band offset of 0.12 ± 0.05 eV was determined in the present study. The accurate determination of the band alignment of the β-Ga2O3/GaAs heterojunction provided useful information for the application in β-Ga2O3/GaAs-based devices.

Effect of the chemical vapor deposition condition on the electrochemically catalytic efficiency for hydrogen evolution reaction in MoS2 nanoparticles

Introduction: Using the metal organic chemical vapor deposition (MOCVD) method, we have synthesized the MoS2 nanoparticles on graphite foil substrates employed as the electrochemical working electrodes with highly efficient electrocatalysis for hydrogen evolution reaction (HER).
 Methods: The morphological and structural properties of the as-grown MoS2 materials were demonstrated by field emission scanning electron microscope (FESEM) and Raman spectroscopies, while their elemental components were investigated by X-ray photoelectron spectroscopy (XPS).
 Results: The optimum growth time was acquired to be 11 hours. Thereby such obtained electrode exhibited the maximum HER activity with onset over the potential of 220 mV versus reversible hydrogen electrode (RHE), and the Tafel slope of 66 mV per decade (mV/dec).
 Conclusion: Our results suggest a good technique for the research of high-efficient HER electrocatalyst based on atomic-thickness layered materials.

S/Mo ratio and petal size controlled MoS2 nanoflowers with low temperature metal organic chemical vapor deposition and their application in solar cells

Vertically aligned two-dimensional (2D) molybdenum disulfide nanoflowers (MoS2 NFs) have drawn considerable attention as a novel functional material with potential for next-generation applications owing to their inherently distinctive structure and extraordinary properties. We report a simple metal organic chemical vapor deposition (MOCVD) method that can grow high crystal quality, large-scale and highly homogeneous MoS2 NFs through precisely controlling the partial pressure ratio of H2S reaction gas, P SR, to Mo(CO)6 precursor, P MoP, at a substrate temperature of 250 °C. We investigate microscopically and spectroscopically that the S/Mo ratio, optical properties and orientation of the grown MoS2 NFs can be controlled by adjusting the partial pressure ratio, P SR/P MoP. It is also shown that the low temperature MOCVD (LT-MOCVD) growth method can regulate the petal size of MoS2 NFs through the growth time, thereby controlling photoluminescence intensity. More importantly, the MoS2 NFs/GaAs heterojunction flexible solar cell exhibiting a power conversion efficiency of ∼1.3% under air mass 1.5 G illumination demonstrates the utility of the LT-MOCVD method that enables the direct growth of MoS2 NFs on the flexible devices. Our work can pave the way for practical, easy-to-fabricate 2D materials integrated flexible devices in optical and photonic applications.

Superconducting protector against electromagnetic pulses based on YBCO film prepared on an Al2O3 substrate with a CeO2 sublayer

The electric and magnetic properties of microbridges made from 440 nm thick Y–Ba–Cu–O films prepared on Al2O3 substrates with CeO2 sublayers by the pulsed injection metal organic chemical vapor deposition (MOCVD) method were studied in temperatures ranging from 20 K to 300 K in order to investigate the possibilities of using these microbridges as fast fault current limiters. The application of an external magnetic field () causes the flux flow induced magneto-resistive effect, which is proportional to and to at low and high temperatures, respectively. The experimentally obtained S-shaped I–V characteristic and the change of the microbridge resistance over time when affected by a step-like magnetic field can be well explained using a thermo-electrical model based on Joule heating and the flux flow nature of the resistive state (RS). The transition from the superconducting to the RS, studied using ns duration rectangular waveform electrical pulses able to create up to ≈2106 A cm−2 current densities without rises of microbridge temperatures, demonstrated that the I–V characteristics of the RSs consisting of an assembly of straight lines corresponding to the different pinning centers. At temperatures close to the critical temperature of superconductivity, the number of these lines increases, and the I–V characteristics can be described with high accuracy by a power law. It was concluded that microbridges made from these films can be used as protectors against complicated waveform electromagnetic pulses having short rise times, high voltage peak amplitudes and long low-value over-current ‘tails’.

Investigation of Structural, Optical and Electrical Properties of Al0.3Ga0.7N/GaN HEMT Grown by MOCVD

In this study, Al0.3Ga0.7N/GaN high electron mobility transistor (HEMT) structure is investigated grown over c- oriented sapphire substrate by using Metal Organic Chemical Vapor Deposition (MOCVD) method. Optical, morphological and electrical characteristics of this structure are determined by X-ray diffraction (XRD), Photoluminecanse (PL), Ultraviolet (UV-Vis.), Atomic Force Microscopy (AFM) and Hall- Resistivity measurements. By using XRD method, 2θ, Full Width at Half Maximun (FWHM), lattice parameters, crystallite size, strain, stress and dislocation values are calculated on symmetric and asymmetric planes. Direct band gap of GaN is determined by PL measurements as 3.24 eV. It is seen that conduction of AlGaN layer starts at 360 nm in UV-Vis. In Hall-Resistivity measurements, it is noticed that carrier density of HEMT structure is not effected by temperature and mobility value is high. Carrier density and mobility values are determined as 5.82x1015 1/cm3 and 1198 cm2/Vs at room temperature respectively. At the lowest temperature point (25 K) they are calculated as 5.19x1015 1/cm3 and 6579 cm2/Vs, respectively.

Anisotropic optical phonons in MOCVD grown Si-doped GaN/Sapphire epilayers

Micro-Raman spectroscopy is employed to study the anisotropic optical phonons of Si-doped GaN/Sapphire epifilms grown by metal organic chemical vapor deposition method. In an undoped 3.6 μm thick sample – our polarized Raman measurements in the backscattering geometry revealed major first order modes of GaN and sapphire. Careful analyses of the second-order Raman spectra using critical-point-phonons from a rigid-ion-model fitted inelastic X-ray spectroscopy data with appropriate selection rules helped us attain expedient data for the lattice dynamics of GaN. In Si-doped films, a modified phonon confinement model is used for simulating Raman line shapes of E2high phonons to monitor crystalline quality. While the optical phonons in lightly doped samples are coupled to electron plasma– at higher carrier concentration the over-damped A1(LO) mode vanished in the background. For each sample we assessed the transport parameters by simulating Raman profiles of A1(LO) line shape with contributions from plasmon-LO-phonon and Lorentzian shaped Eg sapphire mode. A realistic Green’s function theory is adopted to study the vibrational modes of Si donors and Mg acceptors in GaN by including force constant changes estimated from lattice relaxations using first-principles bond-orbital model. Theoretical results of impurity-activated modes compared favorably well with the existing Raman scattering data.

Effects of the deposition temperature on the microwave-absorption performance of Fe/CNT composites

Iron coated carbon nanotube (CNT) nanocomposite absorbents were prepared by a metal organic chemical vapor deposition method using carbonyl iron as the Fe precursor. The microstructures and electromagnetic properties of the composites were characterized by XRD, FESEM, TEM, and a vector network analyzer. Results show that the morphology and microwave absorption properties of these core-shell composites are controlled by changing the deposition temperature. The number of iron nanoparticles deposited on the surface of the CNTs gradually increases with increasing deposition temperature in the range 210–240 oC. Too high a temperature (270 oC) causes agglomeration of the Fe nanoparticles on the surface of the CNTs. When the thickness of the electromagnetic coating is 2.9 mm, the composite prepared at 240 oC has the best microwave absorption, with a maximum absorption bandwidth of 6.1 GHz (10.2-16.3 GHz), a minimum reflectivity of −28.3 dB and an absorption intensity less than −10 dB at 6.1 GHz.

Swanepoel method for AlInN/AlN HEMTs

In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV–Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV–Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.