Temperature Metalorganic Chemical Vapor Deposition Research Articles

Heteroepitaxial AlN growth on c-plane sapphire substrates by ammonia-free high temperature metalorganic chemical vapor deposition

AlN films were hetero-epitaxially grown on c-plane sapphire substrates by ammonia-free high temperature metalorganic chemical vapor deposition (AFHT-MOCVD). The dependence of the AlN growth rate on the flow rate of source gases (H2, N2 and trimethylaluminum (TMA)) and the growth temperature were systematically investigated. The maximum AlN growth rate up to ∼4.0 μm/hour was obtained at the present growth conditions. Based on the experimental results, the possible mechanisms in the AFHT-MOCVD growth concerning the gas reactions are qualitatively discussed. The as-grown AlN epilayers were characterized by high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM) and scanning transmission electron microscope (STEM). The narrow full width at half maximum (FWHM) values of symmetric (0002) and asymmetric (10–12) AlN diffractions are obtained ((0002): 211 arcsec, (10–12): 325 arcsec from a ∼3 μm thick AlN epilayer), showing the potential of the growth technique for the high quality AlN growth.

Behaviours of the lattice-polarity inversion in AlN growth on c-Al2O3 (0001) substrates by ammonia-free high temperature metalorganic chemical vapor deposition

A BF-STEM image and inserted magnified HR-HAADF-STEM images showing the different lattice-polarity of AlN at each position.

In- and out-plane transport properties of chemical vapor deposited TiO2 anatase films

Due to their polymorphism, TiO2 films are quintessential components of state-of-the-art functional materials and devices for various applications from dynamic random access memory to solar water splitting. However, contrary to other semiconductors/dielectric materials, the relationship between structural/morphological and electrical properties at the nano and microscales remains unclear. In this context, the morphological characteristics of TiO2 films obtained by metal–organic chemical vapor deposition (MOCVD) and plasma-enhanced chemical vapor deposition (PECVD), the latter including nitrogen doping, are investigated and they are linked to their in- and out-plane electrical properties. A transition from dense to tree-like columnar morphology is observed for the MOCVD films with increasing deposition temperature. It results in the decrease in grain size and the increase in porosity and disorder, and subsequently, it leads to the decrease in lateral carrier mobility. The increase in nitrogen amount in the PECVD films enhances the disorder in their pillar-like columnar morphology along with a slight increase in density. A similar behavior is observed for the out-plane current between the low temperature MOCVD films and the undoped PECVD ones. The pillar-like structure of the latter presents a lower in-plane resistivity than the low temperature MOCVD films, whereas the out-plane resistivity is lower. The tree-like columnar structure exhibits poor in- and out-plane conductivity properties, whereas pillar-like and dense TiO2 exhibits similar in- and out-plane conductivities even if their morphologies are noticeably different.

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.

Epitaxial and large area Sb2Te3 thin films on silicon by MOCVD.

Antimony telluride (Sb2Te3) thin films were prepared by a room temperature Metal–Organic Chemical Vapor Deposition (MOCVD) process using antimony chloride (SbCl3) and bis(trimethylsilyl)telluride (Te(SiMe3)2) as precursors. Pre-growth and post-growth treatments were found to be pivotal in favoring out-of-plane and in-plane alignment of the crystallites composing the films. A comprehensive suite of characterization techniques were used to evaluate their composition, surface roughness, as well as to assess their morphology, crystallinity, and structural features, revealing that a quick post-growth annealing triggers the formation of epitaxial-quality Sb2Te3 films on Si(111).

Comparison of MOCVD and MBE Regrowth for CAVET Fabrication

In this paper, we demonstrate the fabrication of current aperture vertical electron transistors (CAVET) realized with two different epitaxial growth methods. Templates with a p-GaN current blocking layer (CBL) were deposited by metal organic chemical vapor deposition (MOCVD). Channel and barrier layers were then regrown by either molecular beam epitaxy (MBE) or MOCVD. Scanning electron microscope (SEM) images and atomic force microscope (AFM) height profiles are used to identify the different regrowth mechanisms. We show that an AlN interlayer below the channel layer was able to reduce Mg diffusion during the high temperature MOCVD regrowth process. For the low-temperature MBE regrowth, Mg diffusion was successfully suppressed. CAVET were realized on the various samples. The devices suffer from high leakage currents, thus further regrowth optimization is needed.

Point defect reduction in MOCVD (Al)GaN by chemical potential control and a comprehensive model of C incorporation in GaN

A theoretical framework that provides a quantitative relationship between point defect formation energies and growth process parameters is presented. It enables systematic point defect reduction by chemical potential control in metalorganic chemical vapor deposition (MOCVD) of III-nitrides. Experimental corroboration is provided by a case study of C incorporation in GaN. The theoretical model is shown to be successful in providing quantitative predictions of CN defect incorporation in GaN as a function of growth parameters and provides valuable insights into boundary phases and other impurity chemical reactions. The metal supersaturation is found to be the primary factor in determining the chemical potential of III/N and consequently incorporation or formation of point defects which involves exchange of III or N atoms with the reservoir. The framework is general and may be extended to other defect systems in (Al)GaN. The utility of equilibrium formalism typically employed in density functional theory in predicting defect incorporation in non-equilibrium and high temperature MOCVD growth is confirmed. Furthermore, the proposed theoretical framework may be used to determine optimal growth conditions to achieve minimum compensation within any given constraints such as growth rate, crystal quality, and other practical system limitations.

Effect of post-deposition annealing on low temperature metalorganic chemical vapor deposited gallium oxide related materials

Low temperature metalorganic chemical vapor deposition using trimethylgallium and water was investigated. The surface morphology of the film was almost flat at a deposition temperature below 182°C. This flat film was a mixture of nanocrystalline and amorphous phase. The film deposited at a temperature of 272°C resulted in a nanowire structure. X-ray diffraction measurements revealed that the nanowire film was a mixture of gallium hydroxide, gallium oxyhydroxide, and gallium tohdite or gallium oxide. We also found that post-deposition annealing above 600°C significantly changed the crystal structure of the both flat and nanowire films. Monoclinic gallium oxide phase was dominant after the post-deposition annealing above 600°C.

High Quality Al-Polar AIN Growth on (0001) Sapphire Using Polarity-Selective Thermal Etching by High Temperature Metalorganic Chemical Vapor Deposition.

In this study, we suggest a polarity-selective in-situ thermal etching and re-growth process for the fabrication of high quality Al terminated AIN epilayers by high temperature metalorganic chemical vapor deposition. Mixed-polar AIN layers grown on a thin (5 nm) buffer layer at a high temperature (950 degrees C) exhibited high crystalline quality. Surface morphologies of in-situ thermally etched AIN layers depended on the grain size and distance between grains. Increasing the initial grain size and diminishing the space between grains increased etching depth and width. During re-growth, threading dislocations were bent and annihilated in the vicinity of voids, which were formed by lateral growth of Al-polar AIN regions after thermal etching. Finally, a high quality Al-polar AIN template, as verified by an aqueous KOH solution, was successfully fabricated.

Fabrication of AIN Nano-Structures Using Polarity Control by High Temperature Metalorganic Chemical Vapor Deposition.

This study investigates the crystallographic polarity transition of AIN layers grown by high temperature metalorganic chemical vapor deposition (HT-MOCVD), with varying trimethylaluminum (TMAI) pre-flow rates. AIN layers grown without TMAI pre-flow had a mixed polarity, consisting of Al- and N-polarity, and exhibited a rough surface. With an increasing rate of TMAI pre-flow, the AIN layer was changed to an Al-polarity, with a smooth surface morphology. Finally, AIN nano-pillars and nano-rods of Al-polarity were fabricated by etching a mixed polarity AIN layer using an aqueous KOH solution.

Response Spectrum 0.9-2.65 μm of In<sub>0.82</sub>Ga<sub>0.18</sub>As Detectors by Two-Step Growth Technique

InP/In0.82Ga0.18As/InP heterostructure used for infrared detector were grown on (100) S-doped InP substrates using two-step growth technique by low temperature metal-organic chemical vapor deposition. The growth was performed using TMIn, TMGa, AsH3, and PH3 as growth precursors in a horizontal reactor. The substrates on a graphite susceptor were heated by inductively coupling RF power, their temperatures were detected by a thermocouple, and the reactor pressure was kept at 10000 Pa. The growth structure of detector included In0.82Ga0.18As buffer with the thickness of 100 nm, In0.82Ga0.18As absorption layer with the thickness of 2.8 μm, and the InP cap with the thickness of 0.8 μm. The planar type of p-i-n detector was fabricated by Zn diffusion. The properties of In0.82Ga0.18As detector were studied, the curves of the I-V characteristics, the range of response spectrum, and the detectivity (D*) were obtained.

Activation of ion implanted Si in GaN using a dual AlN annealing cap

A dual annealing cap composed of a thin, low temperature metal-organic chemical vapor deposition (MOCVD) deposited AlN adhesion layer and a thicker, sputtered AlN film for added mechanical strength enabled us to anneal Si-implanted layers for 30 min at temperatures up to 1250 °C. At higher temperatures the cap was destroyed by the large partial pressure of the N2 from the GaN, which exceeds the yield strength of AlN. Electrical activations as high as 70% and electron mobilities comparable to those of in situ doped films were achieved. Compared to other methods, the surfaces are better protected using this cap because it adheres better than sputtered AlN, SiO2, or Si3N4; does not crack like MOCVD grown AlN films deposited at normal temperatures (∼1100 °C); and is stronger than thin MOCVD grown AlN films deposited at low temperatures (∼600 °C). Even though N does not escape, and in so doing, forms thermal etch pits, the surface of the annealed GaN is roughened by solid state diffusion with the surface roughness increasing with the annealing temperature.

Low temperature growth and dimension- dependent photoluminescence efficiency of semiconductor nanowires

Low temperature growth and dimension dependent photoluminescence (PL) efficiency of semiconductor nanowires were investigated with CdS as a model system. The CdS nanowires were prepared with a simple, low temperature metal-organic chemical vapor deposition (MOCVD) process via the vapor–liquid–solid (VLS) mechanism. The low growth temperature of 360 °C was made possible with a newly developed single-source precursor of CdS and by using sputtered Au as the catalyst for the VLS growth. The length and diameter of the nanowires were adjusted by reaction time and sputtering conditions of Au, respectively. Nanowires of up to several μm in length and 20 to 200 nm in diameter were obtained. The PL quantum yield of the nanowires was found to decrease with increasing wire length, but to increase with decreasing wire diameter. This dimension-dependent PL efficiency of one-dimensional nanostructure, unlikely resulting from the quantum size confinement effect, appears to be a new observation that carries application significance.

Electrical Properties of Ultrathin Al2O3 Films Grown by Metalorganic Chemical Vapor Deposition for Advanced Complementary Metal-oxide Semiconductor Gate Dielectric Applications

The electrical properties of ultrathin amorphous Al2O3 films, grown by low temperature metal-organic chemical vapor deposition from aluminum(III) 2,4-pentanedionate and water as co-reactants, were examined for potential applications as gate dielectrics in emerging complementary metal-oxide semiconductor technologies. High-frequency capacitance–voltage and current–voltage techniques were used to evaluate Al2O3 films deposited on silicon oxynitride on n-type silicon (100) substrates, with thickness ranging from 2.5 to 6.5 nm, as a function of postdeposition annealing regimes. Dielectric constant values ranging from 11.0 to11.5 were obtained, depending on the annealing method used. Metal-insulator-semiconductor devices were demonstrated with net equivalent oxide thickness values of 1.3 nm. Significant charge traps were detected in the as-deposited films and were mostly passivated by the subsequent annealing treatment. The main charge injection mechanism in the dielectric layer was found to follow a Poole–Frenkel behavior, with post-annealed films exhibiting leakage current an order of magnitude lower than that of equivalent silicon oxide films.

Electrical Characterization of As and [As+Si] doped GaN Grown by Metalorganic Chemical Vapor Deposition

ABSTRACTElectrical properties of As, Si, and [As+Si] doped GaN films grown on sapphire substrates by low temperature metalorganic chemical vapor deposition have been investigated using temperature dependent Hall-effect and deep level transient spectroscopy measurements. The Hall measurements from the GaN layers show that the concentration decreases with arsine flow (4, 40, and 400 sccm) at all temperatures. The carrier concentration of the Si-doped GaN, on the other hand, increases with the incorporation of arsine flow. This behavior is attributed to the formation of AsGa antisites which act as double donors. A deep level at around 0.82 eV below the conduction in the band gap of As doped GaN is measured by DLTS and is tentatively assigned to arsenic on gallium antisite.

Deposition and Characterization of High Dielectric Thin Films for Memory Device Application

(Pb,La)TiO 3 (PLT) and Pb(Zr,Ti)O 3 (PZT) thin films were deposited on Pt/SiO2/Si substrate by metal-organic chemical vapor deposition (MOCVD) using a solid delivery system. The domain configurations of the deposited PLT thin films were investigated, and the film with a columnar structure exhibited a very stable write/read operation for the domain memory application. Electrical properties of PLT, PZT and rf-sputter-deposited (Ba,Sr)TiO 3 (BST) thin films were measured, and their conduction mechanisms were analyzed. The composition and thickness uniformity of BST thin films deposited by the low temperature MOCVD method on a patterned wafer with 0.15 μm-diameter contact holes were investigated, and complete thickness and composition uniformity were obtained especially for the case of a dome-wall-type chamber with a wall temperature of 450°C.

Low temperature metalorganic chemical vapor deposition of gallium nitride using dimethylhydrazine as nitrogen source

Gallium nitride (GaN) films have been homoepitaxially grown by low pressure metalorganic chemical vapor deposition technique using dimethylhydrazine (DMHy) and trimethylgallium (TMG) as the reactants at low temperatures ranging from 873 to 923 K and a constant pressure of 10 Torr. The potential of utilizing DMHy as a nitrogen source is evaluated through understanding the kinetics of GaN film growth. A growth rate dependency study with respect to DMHy and TMG concentrations indicates that Langmuir–Hinshelwood typed reaction dominates the film growth. From a model fitting to the experimental film growth rate, the adsorption equilibrium constant of DMHy is found to be approximately 1/20 that of TMG, indicating that V/III feed ratio can be reduced down to 20 to obtain a stoichiometric GaN film. Based on X-ray photoelectron spectroscope measurement, the films formed by DMHy, however, accompany significant carbon contamination due to the strong CN bonding in DMHy. The contamination can be relieved effectively by introducing H 2 into the reaction.

Low temperature metalorganic chemical vapor deposition growth of InP using the new precursors pentamethylcyclopentadienylindium(I) and white phosphorus

Low temperature metalorganic chemical vapor deposition growth of InP has been achieved with previously unexplored indium precursor, pentamethylcyclopentadienylindium(I) and white phosphorus rather than traditional sources such as trimethylindium or triethylindium and phosphine. By taking advantage of the low sublimation temperature of new indium precursor, epitaxial InP was obtained at low substrate temperatures ranging between 150°C and 250°C on InP substrates with rather low growth rates of 2–34 Å/min. Optical qualities of grown InP homoepitaxy were analyzed by low-temperature photoluminescence (10 K). Luminescence peaks at 1.419 and 1.418 eV correspond to free excitons and donor bound excitons, respectively. The dominant accidental impurities were donors. Neither acceptor-bound excitons nor significant free electrons to acceptor recombination peaks were observed. The InP epilayers grown on InP substrates at a temperature ranging from 180°C to 230°C had higher intensity and narrower full-width at half-maximum of luminescence peaks than those of the iron-doped, semi-insulating InP substrates.

Thermodynamic model of low temperature metalorganic chemical vapor deposition of GaN

A thermodynamic model is developed to explain low temperature metalorganic chemical vapor deposition of GaN. The two stage epitaxial processes taking into account the physisorbed states on (0001) A and B planes are considered. The physisorbed Ga coverage of both GaN planes is presented as the function of the pressures, temperature, and efficiency of ammonia decomposition. The thermodynamic affinities of each stage of the growth runs are described. The formation conditions of the GaN wurtzite and zinc-blende modifications are discussed. The model developed was applied to estimate the thermodynamic characteristics of low temperature metalorganic chemical vapor deposition of GaN. It is quantitatively shown that the considered growth conditions allows formation of the stable and metastable GaN modifications in the same epitaxial run.

Low temperature metalorganic chemical vapor deposition of conformal silver coatings for applications in high aspect ratio structures

A low temperature metalorganic chemical vapor deposition process has been developed for the growth of conformal silver coatings for applications in reflective mirror arrays, computer chip metallization, and superconducting wire and cable technologies. The process employed the silver source precursor Ag(COD)hfac, where COD=1,5-cyclooctadiene and hfac=1,1,1,5,5,5-hexafluoro 2,4-pentanedionate. Silver films were deposited at wafer temperature, source temperature, and processing pressure in the range of, respectively, 160–240 °C, 80–150 °C, and 0.5–5 Torr. Experiments were carried out in the presence of either argon or hydrogen as coreactant. The resulting films were characterized by Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, x-ray diffraction, and cross-section scanning electron microscopy. These investigations indicated that the silver films were pure, highly specular, and exhibited excellent conformality in 180 nm wide trench structures with 7:1 aspect ratio.