Metalorganic Chemical Vapor Deposition Technique Research Articles

Defect Analysis in a Long-Wave Infrared HgCdTe Auger-Suppressed Photodiode.

Deep defects in the long-wave infrared (LWIR) HgCdTe heterostructure photodiode were measured via deep-level transient spectroscopy (DLTS) and photoluminescence (PL). The n+-P+-π-N+ photodiode structure was grown by following the metal-organic chemical vapor deposition (MOCVD) technique on a GaAs substrate. DLTS has revealed two defects: one electron trap with an activation energy value of 252 meV below the conduction band edge, located in the low n-type-doped transient layer at the π-N+ interface, and a second hole trap with an activation energy value of 89 meV above the valence band edge, located in the π absorber. The latter was interpreted as an isolated point defect, most probably associated with mercury vacancies (VHg). Numerical calculations applied to the experimental data showed that this VHg hole trap is the main cause of increased dark currents in the LWIR photodiode. The determined specific parameters of this trap were the capture cross-section for the holes of σp = 10-16-4 × 10-15 cm2 and the trap concentration of NT = 3-4 × 1014 cm-3. PL measurements confirmed that the trap lies approximately 83-89 meV above the valence band edge and its location.

Comparison of SiNx Dielectric Layer Grown by Plasma‐Enhanced Chemical Vapor Deposition, Low‐Pressure Chemical Vapor Deposition, and Metal‐Organic Chemical Vapor Deposition in Diamond‐ and GaN‐Based Integrated Devices

To address the issue of heat dissipation caused by the high output power density of gallium nitride (GaN) devices, using diamond‐integrated devices is an effective solution. Recent studies have suggested that incorporating a dielectric layer, such as silicon nitride (SiNx), between diamond and GaN can improve adhesion while also reducing thermal boundary resistance (TBR). In this study, plasma‐enhanced chemical vapor deposition (CVD), low‐pressure CVD, and metal‐organic CVD (MOCVD) techniques are utilized to grow the SiNx layer. The interface behavior of diamond/SiNx/GaN is analyzed through scanning electron microscopy, transmission electron microscopy (TEM), scanning TEM, and energy‐dispersive X‐ray spectroscopy, while time‐domain thermoreflectance measurement is used to characterize thermal properties. After analyzing the impact of the growth dielectric layer on the interface thermal resistance of the three growth modes, it is concluded that the dielectric layer produced by the MOCVD technique exhibits a smoother surface and lower TBR compared to the other two methods. Therefore, the use of the MOCVD technique is recommended to achieve optimal thermal performance in diamond/SiNx/GaN systems.

Epitaxial growth of high-quality GaN with a high growth rate at low temperatures by radical-enhanced metalorganic chemical vapor deposition

Using our recently developed radical-enhanced metalorganic chemical vapor deposition (REMOCVD) technique, we have grown gallium nitride (GaN) on bulk GaN and GaN on Si templates. Three features make up this system: (1) applying very high-frequency power (60 MHz) to increase the plasma density; (2) introducing H2 and N2 gas in the plasma discharge region to produce active NHx radical species in addition to nitrogen radicals; and (3) supplying radicals under remote plasma arrangement with a Faraday cage to suppress charged ions and photons. Using this new REMOCVD system, it was found that high-quality crystals can be grown at lower temperatures than that of MOCVD but the disadvantage was that the growth rate was smaller as 0.2–0.8 μm/h than that by MOCVD. In the present work, we have used a pBN inner shield to prevent the deactivation of radicals to increase the growth rate. The growth conditions such as the plasma power, trimethylgallium (TMG) source flow rate, N2 + H2 gas mixture flow rate, and the ratio of N2/H2 were optimized and it was found that the growth rate could be increased up to 3.4 μm/h with remarkably high crystalline quality comparable to that of MOCVD. The XRD-FWHM of GaN grown on the GaN/Si template and the bulk GaN substrate were 977 arcsec and 72 arcsec respectively. This work may be very promising to achieve high-power GaN/GaN devices.

First-principles investigations and MOCVD growth of Si-doped β-Ga2O3 thin films on sapphire substrates for enhancing Schottky barrier diode characteristics

In the realm of high-power electronics, the potential of gallium oxide (β-Ga2O3) as a front-runner material has garnered significant attention due to its wide bandgap and the capacity to withstand high critical electric fields. To push the boundaries of performance for β-Ga2O3 devices, a meticulous exploration into the effects of silicon (Si) doping on β-Ga2O3 films was carried out using the metalorganic chemical vapor deposition (MOCVD) technique with various tetraethoxysilane (TEOS) flow rates (0–30 sccm). The Si-doped β-Ga2O3 films were systematically studied and characterized using XRD, SEM, and XPS techniques. XRD patterns demonstrated the preservation of the β-Ga2O3 monoclinic structure in the Si-doped β-Ga2O3 films, without any evidence of secondary phases. In addition to this, first-principles calculations were performed to explore the incorporation of Si atoms in Ga2O3 supercells, which revealed the preference of Si atoms to occupy substitutional Ga tetrahedral sites within the Ga2O3 lattice. Through the utilization of Si-doped β-Ga2O3 films, a unique design of donut-shaped Schottky barrier diode (SBD) was successfully engineered. Remarkably, the Si-doped β-Ga2O3 SBD (employed with 20 sccm TEOS flow rate) exhibited the breakdown voltage (Vbr) of 497 V and Baliga's Figure of Merit (BFOM) value of 1.16 kW/cm2, which is five-order higher BFOM compared to undoped β-Ga2O3 SBD. This substantial improvement in BFOM underscores the significant potential of Si-doped β-Ga2O3 films for high-power electronics, opening avenues for enhanced device efficiency and capabilities.

Phase-Centric MOCVD Enabled Synthetic Approaches for Wafer-Scale 2D Tin Selenides.

Following an initial nucleation stage at the flake level, atomically thin film growth of a van der Waals material is promoted by ultrafast lateral growth and prohibited vertical growth. To produce these highly anisotropic films, synthetic or post-synthetic modifications are required, or even a combination of both, to ensure large-area, pure-phase, and low-temperature deposition. A set of synthetic strategies is hereby presented to selectively produce wafer-scale tin selenides, SnSex (both x=1 and 2), in the 2D forms. The 2D-SnSe2 films with tuneable thicknesses are directly grown via metal-organic chemical vapor deposition (MOCVD) at 200°C, and they exhibit outstanding crystallinities and phase homogeneities and consistent film thickness across the entire wafer. This is enabled by excellent control of the volatile metal-organic precursors and decoupled dual-temperature regimes for high-temperature ligand cracking and low-temperature growth. In contrast, SnSe, which intrinsically inhibited from 2D growth, is indirectly prepared by a thermally driven phase transition of an as-grown 2D-SnSe2 film with all the benefits of the MOCVD technique. It is accompanied by the electronic n-type to p-type crossover at the wafer scale. These tailor-made synthetic routes will accelerate the low-thermal-budget production of multiphase 2D materials in a reliable and scalable fashion.

Size‐Dependent Characteristics of InGaN‐Based Blue and Green Micro‐Light‐Emitting Diodes

This study focuses on investigating the size‐dependent characteristics (chip diameter: 100–10 μm) of InGaN‐based blue and green micro‐light‐emitting diodes (μLEDs) with respect to their electrical and optical properties. The LED's epistructure is grown using the metal–organic chemical vapor deposition technique, preceded by simulation and optimization using SiLENSe LED simulator. The cross‐sectional transmission electron microscopy study confirms the epistructure. The Photoluminescence mapping of the epistructure reveals that the blue emission is at 461 nm (full width at half maximum [FWHM] ≈ 15.5 nm) and the green emission is at 510 nm (FWHM ≈ 17.5 nm). The study analyzes the size‐dependent external quantum efficiency (EQE), optical power, and peak wavelength shift between blue and green μLEDs. The electroluminescence (EL) study reveals that the redshift of the EL peak wavelength of μLEDs is attributed to the release of strain at reduced chip sizes. The size‐dependent EQE study shows a reduction of EQE with shrunken chip size, attributed to the increase of nonradiative Shockley–Read–Hall recombination. Finally, the study estimates the characteristics temperature of the μLEDs using temperature‐dependent EL measurement, revealing that blue μLEDs exhibit a significantly large value of characteristic temperature ≈1926 K.

The Origin of the Yellow Luminescence Band in Be-Doped Bulk GaN

Photoluminescence (PL) from Be-doped bulk GaN crystals grown by the High Nitrogen Pressure Solution method was studied and compared with PL from GaN:Be layers on sapphire grown by molecular beam epitaxy and metalorganic chemical vapor deposition techniques. The yellow luminescence band in the latter is caused by the isolated BeGa acceptor (the YLBe band), while the broad yellow band in bulk GaN:Be crystals is a superposition of the YLBe band and another band, most likely the CN-related YL1 band. The attribution of the yellow band in bulk GaN:Be crystals to the BeGaON complex (a deep donor) is questioned.

Enhanced solar-driven photoelectrochemical water splitting using nanoflower Au/CuO/GaN hybrid photoanodes.

Harnessing solar energy for large-scale hydrogen fuel (H2) production shows promise in addressing the energy crisis and ecological degradation. This study focuses on the development of GaN-based photoelectrodes for efficient photoelectrochemical (PEC) water splitting, enabling environmentally friendly H2 production. Herein, a novel nanoflower Au/CuO/GaN hybrid structure was successfully synthesized using a combination of methods including successive ionic layer adsorption and reaction (SILAR), RF/DC sputtering, and metal-organic chemical vapour deposition (MOCVD) techniques. Structural, morphological, and optical characteristics and elemental composition of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, and energy-dispersive X-ray (EDX) spectroscopy, respectively. PEC and electrochemical impedance measurements were performed for all samples. The nanoflower Au/CuO/GaN hybrid structure exhibited the highest photocurrent density of ∼4 mA cm-2 at 1.5 V vs. RHE in a Na2SO4 electrolyte with recorded moles of H2 of about 3246 μmol h-1 cm-2. By combining these three materials in a unique structure, we achieved improved performance in the conversion of solar energy into chemical energy. The nanoflower structure provides a large surface area and promotes light absorption while the Au, CuO, and GaN components contribute to efficient charge separation and transfer. This study presents a promising strategy for advancing sustainable H2 production via efficient solar-driven water splitting.

Concurrent Thermal Reduction and Boron-Doped Graphene Oxide by Metal–Organic Chemical Vapor Deposition for Ultraviolet Sensing Application

We synthesized a boron-doped reduced graphene oxide (BrGO) material characterized by various electrical properties, through simultaneous thermal reduction and doping procedures, using a metal–organic chemical vapor deposition technique. X-ray photoelectron spectroscopy (XPS) was used to study the impact of the doping level on the B bonding in the reduced graphene oxide (rGO) layer that is influenced by the annealing temperature. The synthesized BrGO layer demonstrated a high B concentration with a considerable number of O-B bonds, that were altered by annealing temperatures. This resulted in a decreased work function and the formation of a Schottky contact between the BrGO and n-type Si substrate. Due to the higher proportion of B-C and B-C3 bonding in the BrGO/Si device than that in the rGO/Si, the decreased Schottky barrier height of the BrGO/n-Si vertical junction photodetector resulted in a higher responsivity. This study showcases a promise of a simple B-doping method in use to alter the electrical characteristics of graphene materials.

Improved external quantum efficiency of deep UV LEDs with an ultra-thin AlGaN last quantum barrier by controlling the desorption-kinetics process

An ultra-thin AlGaN last quantum barrier (LQB) with a high Al content is effective in enhancing the hole injection in AlGaN-based deep UV LEDs (DUV-LEDs). However, it is very challenging to realize the ultra-thin LQB by the metalorganic chemical vapor deposition technique. In this work, a well-defined 1.0 nm thick AlGaN LQB with unintentionally high Al content was achieved by controlling the surface desorption kinetics for the growth of multiple quantum wells. The light output power of the DUV-LEDs with 1 nm thick LQB was increased by 44% to 7.16 mW at 40 mA, and the peak external quantum efficiency reached 4.04%.

Opto-electronic properties of copper-zinc-sulfide thin films grown via metalorganic-chemical vapor deposition technique at different flow rates

In this work, copper zinc sulfide (CZS) ternary thin films were prepared from the pyrolysis of a Bis-(morpholinodithiato-s,s’)-Cu-Zn precursor using metal-organic chemical vapor deposition technique maintained at 450 °C in ambient nitrogen as the carrier gas. The deposition flow rate was varied to study its effect on the optoelectronic properties of CZS films. The particle-induced x-ray emission technique (PIXE) of the prepared single solid source precursor shows the presence of copper, zinc, and sulfur. The Fourier transform infrared spectrophotometer of the precursor reveals the metal-metal bond attachment to the ligand at a very low wavenumber. The XRD spectra reveal the formation of the hexagonal closed-packed structure of CZS films with a preferred orientation along the [111] direction. The film crystallite size is found to increase from 10.4 to 12.2 nm as the flow rate increases, while the dislocation density and stress decrease as the deposition flow rate increases. The SEM analysis revealed an improvement in the growth rate of the grains as the flow rate increased. The transmittance of the deposited CZS films was found to increase from 58% to 84.2% in the infrared region with an increase in band gap from 3.08–3.64 eV as the flow rate increased. The deposited film shows ohmic properties and an increase in conductivity from 0.243 to 0.847 ( while the resistivity decreases as the flow rate increases. These observations provide room for the deposited CZS film to serve as a potential material for optoelectronics and window layer solar cell devices.

Investigation of carbon incorporation in laser-assisted MOCVD of GaN

Background carbon (C) impurity incorporation in metalorganic chemical vapor deposition (MOCVD) grown gallium nitride (GaN) represents one of the major issues in further improving GaN vertical power device performance. This work presents a laser-assisted MOCVD (LA-MOCVD) technique to address the high-C issue in MOCVD homoepitaxial GaN under different growth rate (Rg) regimes and studies the correlations between [C] and Rg. [C] in LA-MOCVD GaN is reduced by 50%–90% as compared to the conventional MOCVD GaN for a wide growth rate range between 1 and 16 μm/h. A mass-transport based model is developed to understand the C incorporation at different Rg regimes. The results obtained from the developed model are in good agreement with experimental data. The model further reveals that LA-MOCVD effectively suppresses C incorporation by reducing the active C species in the gas phase. Moreover, high step velocity in step flow growth mode can facilitate C incorporation at fast Rg, exhibiting steeper C increase. The theoretical model indicates that [C] can be suppressed below 1016 cm−3 with a fast growth rate (Rg) of 10 μm/h by utilizing higher power LA-MOCVD and freestanding GaN substrates with larger off-cut angles.

Gate-Induced Trans-Dimensionality of Carrier Distribution in Bilayer Lateral Heterosheet of MoS2 and WS2 for Semiconductor Devices with Tunable Functionality

Using the metal–organic chemical vapor deposition technique, we synthesized a bilayer lateral heterostucture of MoS2 and WS2, each of which layers consist of alternately arranged nanostrips of MoS2 and WS2. Transmission electron microscope images exhibit a checked pattern contrast, reflecting the three distinct interlayer metal arrangements of Mo/Mo, W/Mo (Mo/W), and W/W stacking. Theoretical calculations based on the density functional theory elucidated that the bilayer lateral heterostructure of MoS2 and WS2 exhibits complexed type-II band edge alignments depending on the interlayer metal arrangement: The conduction band edge is located at the Mo atom in a Mo/Mo sector, while the valence band edge is located at the W atom in a W/W sector. According to the complexed band edge alignment, the field-induced carrier injection behavior in the bilayer heterosheet composed of MoS2 and WS2 strips shows gate-induced trans-dimensionality, where the accumulated carrier distributions continuously vary from zero- to two-dimensional based on the applied gate voltage. Tunable carrier dimensionality can be applicable for wide areas of electronics, such as quantum dot arrays with tunable dot–dot interaction.

Deposition of stoichiometry – tailored amorphous Cu-S thin films by MOCVD technique

ABSTRACT Deposition technique and associated deposition parameters play significant roles in determining the stoichiometry of thin films, and consequently, their properties. Herein, Cu-S thin films were deposited on a sodalime glass substrate via metal organic chemical vapour deposition (MOCVD) at temperatures between 350 and 450°C using a single solid source precursor. The deposited Cu-S films were characterized using Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometry, and four-point probe technique. RBS characterization revealed that the films are non-stoichiometry while thickness increased from 480 to 655 nm as deposition temperature increased. SEM revealed micrographs that are temperature-dependent. A direct band gap value between 2.75 and 3.80 eV was obtained as the deposition temperature increased. Electrical characterization showed ohmic characteristics in which, resistivity decreased from 18.50 × 10−3 Ωcm to 8.20 × 10−3 Ωcm as deposition temperature increased.

TỔNG HỢP VẬT LIỆU NANO THẤP CHIỀU LÕI-VỎ MoS2\TiO2 ỨNG DỤNG TRONG XÚC TÁC ĐIỆN HÓA SINH KHÍ H2

In this report, we present the synthesis of low dimensional shell-core (2D\1D) nanostructures, in which the TiO2 nanorods (TNRs) as the core are covered by a continuous monolayer MoS2 (1L-MoS2) as the shell. The obtain 1L-MoS2\TNRs was directly grown on the conduct graphite foil without any transfer process, thus minimizing the charge transfer resistance from the electrode to the outer most working surface. For the first steps, the TiO2 seed layer was designed by the AF sputtering method, then the TNRs were grown by hydrothermal approach. Thereafter, the TNRs were conformally coated by a continuous monolayer MoS2 via a metal-organic chemical vapor deposition technique, resulting in 1L-MoS2\TNRs nanomaterial. The structural, vibrational, and morphological characteristics demonstrated that the samples are high crystallinity. Interestingly, the 1L-MoS2\TNRs showed highly efficient in electrochemical HER activity with the smallest onset overpotential of -140 mV vs RHE and a corresponding Tafel slope of 80 mV per decade, which were much lower compared to the pristine 1L-MoS2 and TNRs.

Engineering of NiO/ZnO Core-Shell Nanostructure via Facile Chemical Processes for Environmental Application

NiO/ZnO core–shell nanoflakes structures were successfully fabricated using a unique strategy consisting of a simple chemical bath deposition (CBD) route followed by a metal-organic chemical vapor deposition (MOCVD) technique with different growth times. The XRD results combined with Raman measurements and X-ray photoelectron spectroscopy confirmed that the surface property and photocatalytic activity of NiO/ZnO core–shell nanostructures affected by varying the growth time of ZnO on the surface of NiO nanoflakes. The Scanning electron microscopy images exhibited that the NiO/ZnO samples have a porous core–shell architecture with high surface area and abundant open sites, resulting in enhanced photocatalytic activity. The photocatalytic activity was tested for the prepared samples by measuring the degradation of crystal violet (CV) dye under ultraviolet irradiation. NiO/ZnO core–shell nanostructures deposited at 30 min exhibits higher photodegradation efficiency toward CV dye compared to NiO/ZnO core–shell deposited at 60 min and NiO nanoflakes standing alone. The enhanced photocatalytic activity is due to the formation of p–n heterojunction between ZnO and NiO with a high specific area and more active site of core–shell nanoflakes architecture. The obtained results in this research suggest a new strategy for the fabrication of highly efficient photocatalytic activity semiconducting metal oxide with core–shell.

Spectromicroscopy Studies of Silicon Nanowires Array Covered by Tin Oxide Layers.

The composition and atomic and electronic structure of a silicon nanowire (SiNW) array coated with tin oxide are studied at the spectromicroscopic level. SiNWs are covered from top to down with a wide bandgap tin oxide layer using a metal-organic chemical vapor deposition technique. Results obtained via scanning electron microscopy and X-ray diffraction showed that tin-oxide nanocrystals, 20nm in size, form a continuous and highly developed surface with a complex phase composition responsible for the observed electronic structure transformation. The "one spot" combination, containing a chemically sensitive morphology and spectroscopic data, is examined via photoemission electron microscopy in the X-ray absorption near-edge structure spectroscopy (XANES) mode. The observed spectromicroscopy results showed that the entire SiNW surface is covered with a tin(IV) oxide layer and traces of tin(II) oxide and metallic tin phases. The deviation from stoichiometric SnO2 leads to the formation of the density of states sub-band in the atop tin oxide layer bandgap close to the bottom of the SnO2 conduction band. These observations open up the possibility of the precise surface electronic structures estimation using photo-electron microscopy in XANES mode.

Bi2Te2Se and Sb2Te3 heterostructure based photodetectors with high responsivity and broadband photoresponse: experimental and theoretical analysis.

Topological insulators have emerged as one of the most promising candidates for the fabrication of novel electronic and optoelectronic devices due to the unique properties of nontrivial Dirac cones on the surface and a narrow bandgap in the bulk. In this work, the Sb2Te3 and Bi2Te2Se materials, and their heterostructure are fabricated by metal-organic chemical vapour deposition and evaporation techniques. Photodetection of these materials and their heterostructure shows that they detect light in a broadband range of 600 to 1100 nm with maximum photoresponse of Sb2Te3, Bi2Te2Se and Sb2Te3/Bi2Te2Se at 1100, 1000, and 1000 nm, respectively. The maximum responsivity values of Sb2Te3, Bi2Te2Se, and their heterostructure are 183, 341.8, and 245.9 A W-1 at 1000 nm, respectively. A computational study has also been done using density functional theory (DFT). Using the first-principles methods based on DFT, we have systematically investigated these topological insulators and their heterostructure's electronic and optical properties. The band structures of Sb2Te3 and Bi2Te2Se thin films (3 QL) and their heterostructure are calculated. The bandgaps of Sb2Te3 and Bi2Te2Se are 26.4 and 23 meV, respectively, while the Sb2Te3/Bi2Te2Se heterostructure shows metallic behaviour. For the optical properties, the dielectric function's real and imaginary parts are calculated using DFT and random phase approximation (RPA). It is observed that these topological materials and their heterostructure are light absorbers in a broadband range, with maximum absorption at 1.90, 2.40, and 3.21 eV.

AlInN/AlN HEMT’in Detaylı Optik Özellikleri

In this study, the optical properties of AlInN/AlN high electron mobility transistor (HEMT) structure, grown on c-oriented sapphire with Metal-Organic Chemical Vapor Deposition (MOCVD) technique, being investigated. Optical characterization is made Kubelka- Munk method. Transmittance, absorbance, and reflectance are investigated in detail. Also, the Kubelka-Munk theory is employed to determine the forbidden energy band gap of InN by using special functions. The energy band gap obtained by this method was compared.

Parasitic behavior of different V/III ratios on the properties of InGaN/GaN heterostructures by MOCVD technique

In this study, InGaN/GaN heterostructures were grown on a c-plane flat sapphire substrate (FSS) by using the metalorganic chemical vapor deposition (MOCVD) technique. The flow rates of the ammonia gas varied from 9 SLM to 24 SLM for the growth of InGaN thin film, which was equivalent to the V/III ratio of 6211–16562. Results indicated that a higher V/III ratio promotes parasitic behavior by hydrogen dissociated from ammonia. The parasitic behavior from hydrogen species etches the InN away from the growing surface and transforms the growth morphology from 3D islands to 2D growth mode. A slight reduction in indium composition was observed when increasing the V/III ratio. Next, more stable bandgap energy was observed for the InGaN thin films grown at higher V/III ratios. Improvements in electrical properties in terms of electron mobility and sheet resistance were observed at a higher V/III ratio which is associated with the improvement of crystalline quality and less defect density at a higher V/III ratio. The correlation of strain and carrier density of the thin films was further discussed. It was concluded that the growth of high crystalline quality and thick InGaN thin film was possible for solar cell applications at higher V/III ratio growth conditions.