Ammonia (NH3) is commonly used as group V precursor in gallium nitride (GaN) metalorganic chemical vapor deposition (MOCVD). The high background carbon (C) impurity in MOCVD GaN is related to the low pyrolysis efficiency of NH3, which represents one of the fundamental challenges hindering the development of high purity thick GaN for vertical high power device applications. This work uses a laser-assisted MOCVD (LA-MOCVD) growth technique to address the high-C issue in MOCVD GaN. Carbon dioxide (CO2) laser with wavelength of 9.219 um was utilized to facilitate NH3 decomposition via resonant vibrational excitation. The LA-MOCVD GaN growth rate (as high as 10 um/hr) shows a strong linear relationship with the trimethylgallium (TMGa) flow rate, indicating high effective V/III ratios and hence efficient NH3 decomposition. Pits-free surface morphology of LA-MOCVD GaN was demonstrated for films with growth rate as high as 8.5 um/hr. The background [C] in LA-MOCVD GaN films decreases monotonically as the laser power increases. A low [C] at 5.5E15 cm-3 was achieved in LA-MOCVD GaN film grown with the growth rate of 4 um/hr. Charge transport characterization of LA-MOCVD GaN films reveals high crystalline quality with room temperature mobility >1000 cm2/Vs. LA-MOCVD growth technique provides an enabling route to achieve high quality GaN epitaxy with low-C impurity and fast growth rate simultaneously. This technique can also be extended for epitaxy of other nitride-based semiconductors.
We report on the growth and characterization of metalorganic vapor-phase epitaxy-grown \b{eta}-(AlxGa1-x)2O3/\b{eta}-Ga2O3 modulation-doped heterostructures. Electron channel is realized in the heterostructure by utilizing a delta-doped \b{eta}-(AlxGa1-x)2O3 barrier. Electron channel characteristics are studied using transfer length method, capacitance-voltage and Hall measurements. Hall sheet charge density of 1.06 x 1013 cm-2 and mobility of 111 cm2/Vs is measured at room temperature. Fabricated transistor showed peak current of 22 mA/mm and on-off ratio of 8 x 106. Sheet resistance of 5.3 k…
We report on silicon delta doping of metalorganic vapor-phase epitaxy-grown \b{eta}-Ga2O3 thin films using silane precursor. Delta-doped \b{eta}-Ga2O3 epitaxial films are characterized using capacitance-voltage profiling and secondary-ion mass spectroscopy. Electron sheet charge density in the range of 2.9e12 cm-2 to 8e12 cm-2 with a half width at half maximum ranging from 6.2 nm to 3.5 nm is measured. We also demonstrate a high density (6.4e12 cm-2) degenerate two-dimensional electron gas using a delta-doped \b{eta}-(Al0.26Ga0.74)2O3/\b{eta}-Ga2O3 heterostructure.The total charge could also i…
In this work, we report on the growth of high-mobility $β$-Ga$_2$O$_3$ homoepitaxial thin films grown at a temperature much lower than the conventional growth temperature window for metalorganic vapor phase epitaxy. Low-temperature $β$-Ga$_2$O$_3$ thin films grown at 600$^{\circ}$C on Fe-doped (010) bulk substrates exhibits remarkable crystalline quality which is evident from the measured room temperature Hall mobility of 186 cm$^2$/Vs for the unintentionally doped films. N-type doping is achieved by using Si as a dopant and controllable doping in the range of 2$\times$10$^{16}$ - 2$\times$10$…
We report on low-temperature MOVPE growth of silicon delta-doped \b{eta}-Ga2O3 films with low FWHM. The as-grown films are characterized using Secondary-ion mass spectroscopy, Capacitance-Voltage and Hall techniques. SIMS measurements show that surface segregation is the chief cause of large FWHM in MOVPE-grown films. The surface segregation coefficient (R) is observed to reduce with reduction in the growth temperature. Films grown at 600 °C show an electron concentration of 9.7 x 1012 cm-2 and a FWHM of 3.2 nm. High resolution scanning/transmission electron microscopy of the epitaxial film di…
High-reflectance group III-nitride distributed Bragg reflectors (DBRs) were deposited by MOCVD on Si (111) substrates. A reflectance greater than 96% was demonstrated for the first time for an AlN/GaN DBR with a stop-band centered in the blue-green range of the visible spectrum. Crack-free GaN cap layers were grown on the DBR structures to demonstrate the opportunity to build III-nitride optoelectronic devices in this material. The DBR structure was under significant strain due to growth on a mismatched substrate although the GaN cap layer was shown to be strain free.
This report introduces the electromagnetic absorption of the catalyst as a novel knob in optimizing chemical vapor deposition of graphene. A chromium film initially deposited at one side of a catalyst copper foil absorbs radiative thermal energy several times higher than the plain copper foil and migrates to the other side of the foil in the form of microscale grains. The process involves local melting of the copper which together with the increased operation temperature, improves the crystalline quality of growing graphene. Local melting of copper replaces the otherwise-necessary annealing pr…
Theoretical calculations and experimental observations show MoTe2 is a type II Weyl semimetal, along with many members of transition metal dichalcogenides family. We have grown highly crystalline large-area MoTe2 thin films on Si/SiO2 substrates by chemical vapor deposition. Very uniform, continuous, and smooth films were obtained as confirmed by scanning electron microscopy and atomic force microscopy analyses. Measurements of the temperature dependence of longitudinal resistivity and current-voltage characteristics at different temperature are discussed. Unsaturated, positive quadratic magne…
Great achievements have been made in alloying of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), which can allow tunable band gaps for practical applications in optoelectronic devices. However, telluride-based TMDs alloys were less studied due to the difficulties of sample synthesis. Here, in this work we report the large-area synthesis of 2D MoTexSe2-x alloy films with controllable Te composition by a modified alkali metal halides assisted chemical vapor deposition method. The as-prepared films have millimeter-scale transverse size. Raman spectra experiments combi…
The engineering of defects in diamond, particularly nitrogen-vacancy (NV) centers, is important for many applications in quantum science. A materials science approach based on chemical vapor deposition (CVD) growth of diamond and in-situ nitrogen doping is a promising path toward tuning and optimizing the desired properties of the embedded defects. Herein, with the coherence of the embedded defects in mind, we explore the effects of substrate miscut on the diamond growth rate, nitrogen density, and hillock defect density, and we report an optimal angle range between 0.66° < θ < 1.16° for the p…
Metal organic chemical vapor deposition (MOCVD) is one of the main methodologies used for thin film fabrication in the semiconductor industry today and is considered one of the most promising routes to achieve large-scale and high-quality 2D transition metal dichalcogenides (TMDCs). However, if not taken special measures, MOCVD suffers from some serious drawbacks, such as small domain size and carbon contamination, resulting in poor optical and crystal quality, which may inhibit its implementation for the large-scale fabrication of atomic-thin semiconductors. Here we present a Growth-Etch MOCV…
We present a novel transparent conductive support structure for two-dimensional (2D) materials that provides an electronically passive 2D/3D interface while also enabling facile interfacial charge transport. This structure, which comprises an evaporated nanocrystalline carbon (nc-C) film beneath an atomic layer deposited alumina (ALD AlOx) layer, is thermally stable and allows direct chemical vapor deposition (CVD) of 2D materials onto the surface. When the nc-C/AlOx is deposited onto a 270 nm SiO2 layer on Si, strong optical contrast for monolayer flakes is retained. Raman spectroscopy reveal…
The study of two- dimensional (2D) materials is a rapidly growing area within nanomaterial research. However, the high equipment costs, which include the processing systems necessary for creating these materials, can be a barrier to entry for some researchers interested in studying these novel materials. Such process systems include those used for chemical vapor deposition. This article presents the first open-source design for an automated chemical vapor deposition system that can be built for less than a third of the cost for a similar commercial system. Our design can be easily customized a…
Spot Profile Analysis Low Energy Electron Diffraction of Plasma-Enhanced Chemical Vapor Deposition Grown Epitaxial Few-Layer Graphene on Sapphire
University of Duisburg-Essen（杜伊斯堡-埃森大学）；Faculty of Engineering, University of Duisburg-Essen（杜伊斯堡-埃森大学工程学院）；Department of Chemistry and Waterloo Institute for Nanotechnology（化学系与滑铁卢纳米技术研究所）；Center for Nanointegration (CENIDE)（纳米集成中心）
Two-dimensional materials such as transitional metal dichalcogenides exhibit unique optical and electrical properties. Here we report on the varying optical properties of CVD grown MoS2 monolayer flakes with different shapes. In particular, it is observed that the perimeter and the central region of the flakes have non-uniform photoluminescence (PL) energy and intensity. We quantified these effects systematically and propose that thermally induced strain during growth is the origin. The strain relaxation after transfer of the MoS2 flakes supports this explanation. Detailed investigations of th…
The surface reconstruction of the Fe catalyst films due to high temperature processing in hydrogen prior to nanotube nucleation and its effect on the growth morphologies of partially filled carbon nanotubes (CNTs) synthesized using atmospheric pressure chemical vapor deposition (APCVD) of propane was investigated. Results show that pre-heating of the catalyst film deeply influences the particle size distribution, which governs the growth morphologies of the corresponding CNTs. The distribution of the catalyst particles over the Si substrate was analyzed before and after the heat treatment by a…
Thin film deposition technologies boost the development of modern semiconductor industries. Being a fancy variant, vapor phase deposition on metal nanoparticles (often in liquid phase) rather than on bare substrates opens novel avenues of fabricating low-dimensional nanomaterials, which renders the development of new device architectures and their applications in advanced electronics, optoelectronics and photonics, etc. Since the last twenty years, nanomaterials with various geometries (i.e. dots, wires, trees, tubes, flakes, ribbons, etc.) have been synthesized via different bottom-up methods…
Solution-based methods represent the most widespread approach used to deposit hybrid organic-inorganic perovskite films for low-cost but efficient solar cells. However, solution-process techniques offer limited control over film morphology and crystallinity, and most importantly do not allow sequential film deposition to produce perovskite-perovskite heterostructures. Here the successful deposition of CH3NH3PbI3 (MAPI) thin films by RF-magnetron sputtering is reported, an industry-tested method to grow large area devices with precisely controlled stoichiometry. MAPI films are grown starting fr…
We introduce a novel nanofabrication technique to directly deposit catalyst pads for the chemical vapor deposition synthesis of single-walled carbon nanotubes (SWCNTs) at any desired position on a substrate by Gallium focused ion beam (FIB) induced deposition of silicon oxide thin films from the metalorganic Tetraethyl orthosilicate (TEOS) precursor. A high resolution in the positioning of the SWCNTs is naturally achieved as the imaging and deposition by FIB are conducted concurrently in situ at the same selected point on the substrate. This technique has substantial advantages over the curren…
Recently, graphene is of highly interest owing to its outstanding conductivity, mechanical strength, thermal stability, etc. Among various graphene synthesis methods, atmosphere pressure chemical vapor deposition (APCVD) is one of the best synthesis one due to very low diffusitivity coefficient and a critical step for graphene-based device fabrication. High-temperature APCVD processes for thin film productions are being recognized in many diversity technologies such as solid-state electronic devices, in particular, high quality epitaxial semiconductor films for silicon bipolar and metal oxide …
Two-dimensional semiconducting transition metal dichalcogenides embedded in optical microcavities in the strong exciton-photon coupling regime may lead to promising applications in spin and valley addressable polaritonic logic gates and circuits. One significant obstacle for their realization is the inherent lack of scalability associated with the mechanical exfoliation commonly used for fabrication of two-dimensional materials and their heterostructures. Chemical vapor deposition offers an alternative scalable fabrication method for both monolayer semiconductors and other two-dimensional mate…
A fast optical spectroscopic method for determination rotational ($T_{rot}$) and vibrational ($T_{vib}$) temperatures in two-temperature Boltzmann distribution of the excited state by using machine learning approach is presented. The method is applied to estimate molecular gas temperatures in a direct current glow discharge in hydrogen-methane gas mixture during plasma-enhanced chemical vapor deposition of carbon film materials. Slightly resolved ro-vibrational optical emission spectrum of the $C_2$ ($ν'=0 \to ν''=0$) Swan band system was used for local temperature measurements in plasma ball.…
