Homoepitaxial Growth Research Articles

Selectively buried growth of heavily B doped diamond layers with step-free surfaces in N doped diamond (1 1 1) by homoepitaxial lateral growth

In this work, we proposed a novel method to form a buried heavily boron (B) doped p+-structure with a step-free diamond surface in nitrogen doped diamond (111) based on homoepitaxial lateral growth technique. The buried structure with a size of 10 µm × 10 µm × 0.085 µm was fabricated by inductively coupled plasma (ICP) etching of the mesa structure and subsequent heavy B-doping, with a boron to carbon (B/C) ratio of 15,000 ppm in the microwave-plasma-assisted chemical vapor deposition (MPCVD). The surface morphology of the buried area and its surrounding were observed by laser microscopy (LM) and atomic force microscopy (AFM), which showed atomically flat surfaces before and even after B doping. Surface potential difference measurements on both areas were applied using Kelvin-probe force microscopy (KFM). The intensity imaging of B concentration in and around the buried areas were measured by dynamic secondary ion mass spectrometry (SIMS), which confirmed the heavy B doping of the buried structure and the depth profile shows that B doping is uniform, with a concentration of 2 × 1020 atoms/cm3.

Emergence of local geometric laws of step flow in homoepitaxial growth.

Below the roughening transition, crystal surfaces exhibit nanoscale line defects, steps, that move by exchanging atoms with their environment. In homoepitaxy, we analytically show how the motion of a step train in vacuum under strong desorption can be approximately described by nonlinear laws that depend on local geometric features such as the curvature of each step, as well as suitably defined effective terrace widths. We assume that each step edge, a free boundary, can be represented by a smooth curve in a fixed reference plane for sufficiently long times. Besides surface diffusion and evaporation, the processes under consideration include kinetic step-step interactions in slowly varying geometries, material deposition on the surface from above, attachment and detachment of atoms at steps, step edge diffusion, and step permeability. Our methodology relies on boundary integral equations for the adatom fluxes responsible for step flow. By applying asymptotics, which effectively treat the diffusive term of the free boundary problem as a singular perturbation, we describe an intimate connection of universal character between step kinetics and local geometry.

Homoepitaxial overgrowth of (111) diamond films on Au-coated and Ni-coated substrates

Homoepitaxial growth of (111)-oriented diamond films on the Au-coated and Ni-coated diamond substrates by microwave plasma chemical vapor deposition (CVD) has been investigated. The process is involved with overgrowth of CVD diamond on Au and Ni islands formed by hydrogen plasma annealing of the 20 nm Au and Ni film coatings on diamond substrates. Cross-sectional transmission electron microscopy (TEM) observations show that both of the Au and Ni islands as single crystallites are in epitaxy with diamond substrate and no diamond growth occurs on top of those islands in the early stage of diamond deposition. The overgrowth of diamond over the metal islands results in excellent coalescence to form a continuous film with a lower defect density than the film without the metal coating. With such Au and Ni islands, the film stress can be further relaxed as shown with Raman spectroscopy.

Effect of substrate orientation on homoepitaxial growth of β -Ga2O3 by halide vapor phase epitaxy

The influence of substrate orientation on homoepitaxial growth of beta-gallium oxide by halide vapor phase epitaxy was investigated. Substrates were cut at various angles Δb from the (001) plane (Δb = 0°) to the (010) plane (Δb = 90°) of bulk crystals grown by the edge-defined film-fed growth method. The growth rate increased with increasing absolute value of Δb near the (001). However, from the (001) to the (010), as Δb increased, the growth rate decreased sharply, and streaky grooves observed in the grown layer on the (001) substrate became triangular pits. The length of the pits decreased with increasing Δb, and a pit-free homoepitaxial layer grew at Δb ≈ 60°. The valley line of the pits was parallel to the [010] direction; therefore, the length of the pits decreased with increasing Δb. In addition, transmission electron microscopy observations of the deepest part of a pit revealed that the pits originate from dislocations propagating in the substrate at an angle of 60° with respect to the (001) plane. Therefore, pits are not formed on the grown layer surface when the Δb of the substrate is ∼60°, because its surface is substantially parallel to the dislocations. The homoepitaxial growth of a pit-free layer on the (011) substrate (Δb = 61.7°) was demonstrated, and void defects and dislocations in the substrate were confirmed by the etch-pit method to not be inherited by the homoepitaxial layer.

Vapor-Phase Living Assembly of π-Conjugated Organic Semiconductors.

In contrast to well-studied amphiphilic block copolymers (BCPs) and π-stacked dyes, living assembly of hydrophobic π-conjugated materials has not yet been explored to date. Using a microspacing physical vapor transport (PVT) technique, the prefabricated microrods of organic semiconductors involving 9,10-dicyanoanthracene (DCA, A) or its binary alloy (B) can act as seeds to initiate living homoepitaxial growth from their ends, giving elongated microrods with controlled length. Red-green-red tricolor fluorescent microrod heterostructures with low dispersity are further realized by living heteroepitaxial growth of B microrod blocks on A seed microrod tips. Upon varying the growth sequence of each block, reverse triblock microrods are also accessible. Such a seed-induced living growth is applicable to triblock microrod heterostructures of more binary combinations as well as even more complex penta- and hepta-block heterostructures comprising A and B. By virtue of a convenient vapor-phase growth method, the present work demonstrates the generality of living assembly of π-conjugated materials.

Effect of substrate crystalline orientation on boron-doped homoepitaxial diamond growth

Boron-doped diamond layers have been grown by MW PECVD on substrates with a misorientation over the range of 0 to 90° relative to the (100) crystalline plane while keeping all other growth conditions constant. Deposited layers were characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. The deposition rate, surface roughness, and boron incorporation vary according to the substrate misorientation. These results show the essential need for rigorous control of the substrate crystalline orientation in the synthesis of doped diamond for electronic applications. Thick, smooth, and free of surface defects boron-doped epitaxial diamond layers were obtained over a broad range of crystalline orientations at high growth rates and high boron incorporation efficiency. Novelty statementThis work reports on the effect of the substrate crystalline orientation on the morphology, growth rate, and boron incorporation in epitaxial diamond layers deposited by plasma-enhanced chemical vapor deposition.

Ultrathin DDR Films with Exceptionally High CO2 Flux and Uniformly Adjustable Orientations

AbstractThin and oriented zeolite films are important for advanced separations, catalysis, and sensing. Strategies for tailoring zeolites for applications include controlling their crystal size, shape, and orientation. Here, three siliceous DDR zeolite ultrathin films with different orientations achieved by homoepitaxial growth from 60 nm‐sized seed particles are reported. The 0.5 µm thick membrane shows a separation selectivity of 400 for CO2–CH4 mixtures and CO2 permeance of 25 × 10‐7 mol m‐2 s‐1 Pa‐1 at 20 °C and 1 bar, leading to a record‐high performance among all reported DDR membranes. Furthermore, the seed nanoparticles are grown into mono‐dispersed DDR sub‐micron crystals with trigonal and tabular habits. These crystals are assembled in monolayers for the growth of ultrathin and uniformly (h0h)‐oriented and c‐oriented films with maximum surface pore diameter of 0.365 and 0.263 nm, respectively, by using the 1‐adamantanamine template in fluoride medium. The novel strategy not only provides high‐performance membrane candidates for industrial CO2 separation, but also inspires interfacial engineering, pore size, and orientation controlling for other microporous crystals, and their membranes.

Effect of high temperature homoepitaxial growth of β-Ga2O3 by hot-wall metalorganic vapor phase epitaxy

The effect of high temperature homoepitaxial growth of (010) β-Ga2O3 layer by low pressure hot-wall metalorganic vapor phase epitaxy was investigated. In the growth-temperature range 800–1000 °C, the growth rate decreased with increasing growth temperature and the growth mode changed from three-dimensional island growth to two-dimensional step-flow growth. At 1000 °C, a smooth, twin-free single-crystalline homoepitaxial layer with a structural quality equivalent to that of the substrate could be grown. As the growth temperature increased, the concentration of precursor-derived C impurities decreased, while that of unintentionally incorporated Si impurities increased. It was found that the grown layers were all n-type and showed an effective donor concentration approximately equal to the Si impurity concentration regardless of the C impurity concentration.

Investigation of growth mode and surface roughness during homoepitaxial growth of silver metal using kinetic Monte Carlo simulation

In this work, a kinetic Monte Carlo (KMC) method for deposition is investigated to simulate the homoepitaxial growth of silver metal under experimental conditions. On-lattice and coarse-graining approximations are applied. KMC method is an ideal tool for simulating the Physical Vapor Deposition (PVD) process, which involves deposition and diffusion. The method accounts for surface diffusion processes, in addition to nearest-neighbor hopping and including Schwoebel-Ehrlich (SE). The SE mechanism effect on the growth mode and influences of substrate temperature and deposition rate on surface roughness have been studied in detail. The simulation results show when the Schwoebel hops are active, the growth mode is Frank-van der Merwe (2D). Furthermore, when the Schwoebel hops are not active, the growth mode is Volmer-Weber (3D). In addition, when increasing the deposition rate, the surface roughness increases due to the size of islands increase. Besides, when the temperature increases, the surface roughness decreases because the islands formed are transformed into a large cluster.

Templates for homoepitaxial growth of 3C-SiC obtained by direct bonding of silicon carbide wafers of differing polytype

An approach of direct bonding of SiC wafers of differing polytypes has been implemented in order to create a template for cubic 3C-SiC homoepitaxy. Heteroepitaxial 3C-SiC layers grown by chemical vapor deposition were transferred onto a hexagonal 6H-SiC wafer. The results of structural characterization showed that the quality of 3C-SiC sublimation epitaxy on the templates is comparable to the level of epitaxy of cubic silicon carbide by chemical vapor deposition method. It was confirmed that the 3C-SiC layer transferred onto the 6H-SiC substrate plays the role of a crystalline "seed" that determines cubic polytype of the overgrown SiC layer. Keywords: Silicon carbide, polytypes, direct bonding, templates, sublimation epitaxy.

Homoepitaxial growth of high-quality GaN nanoarrays for enhanced UV luminescence

Crystalline GaN nanoarrays with good alignment and strong UV luminescence have been homoepitaxially grown on a [0001]-oriented GaN substrate due to their superior lattice and thermal conductivity matching with the beneath GaN substrate (see figure).

Novel homo-epitaxial approaches in solvothermal synthesis for preparing surface tethered uni-directionally oriented zinc oxide micro and nano structured arrays

Surface aligned, uni-directionally grown, hexagonal nanorod bundles and microrod pillared arrays of zinc oxide (ZnO), were synthesized through a simple, homo-epitaxial growth approach. A uniform layer of ZnO seed was initially prepared on cleaned glass substrates by dip coating and calcination. Uni-directionally oriented ZnO micro– nano structures were subsequently developed on the seeded glass substrates through solvothermal methods, by employing equi-molar solutions of zinc nitrate and hexamethylenetetramine. The reaction parameters that control the surface morphologies and crystal orientations were explored. A solution exchange process was also carried out to prepare perpendicularly aligned ZnO nanorod arrays. The structural and functional features of the resultant samples were studied and discussed with the help of X-ray diffractometry, scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectrophotometry. A plausible structure dependent growth mechanism of the morphologically varied ZnO was also proposed.

Homoepitaxial lateral growth of single-crystal diamond with eliminating PCD rim and enlarging surface area

Avoiding the appearance of polycrystalline diamond (PCD) rim during the epitaxial lateral outward growth of single-crystal diamond (SCD) by microwave plasma chemical vapor deposition (MPCVD) is still full of difficulties and challenges. Herein, the enlarged SCD without PCD rim was synthesized via different growth modes. The core strategy is the self-formation of off-angles on (001) crystal face by regulating the radicals distribution and reducing the temperature at the seed edge. Therefore, the appearance of the secondary nucleation at the edge regions can be inhibited. In a dual-substrate reactor, the SCD surface displayed a typical terrace flow growth pattern. The growth steps on the SCD surface are directed from the center to the edge which coincides with the distribution of carbon-related radicals and temperature. In addition, a spiral growth mode appeared in the homoepitaxial growth of SCD by a single-substrate reactor. Under a spiral growth mode, the top surface of SCD in an off-axis direction was contributed to form a smooth interface. The SCD surface increased by 88.15% from 3 × 3 mm2 to 4.11 × 4.12 mm2 after 82 h. And the crystalline quality of the CVD epitaxial layer is higher than that of the type Ib seed.

Microstructure Analysis of GaN Epitaxial Layers During Ion Implantation Using Synchrotron X-Ray Topography

Power electronic devices based on wide band-gap semiconductor materials such as GaN and SiC are rapidly being developed to replace traditional silicon-based devices whose performance has nearly reached their material limits. In the fabrication of GaN vertical power devices, selective area doping (SAD) processes are essential [1]. Several SAD techniques have been developed, including ion implantation [2], etching and regrowth method [3, 4], diffusion doping and neutron transmutation [5]. However, the influences of these procedures on the microstructures of GaN epitaxial layers is one of the key factors to determine the performance of the devices.In this study, ion-implanted GaN epitaxial layers from different stages including ammonothermal grown substrate material, metal organic chemical vapor deposition (MOCVD) epitaxial growth, ion implantation and subsequent annealing was characterized by synchrotron monochromatic beam X-ray topography (SMBXT) [6], synchrotron X-ray rocking curve topography (SXRCT) [7], and high-resolution X-ray diffraction (HRXRD). The change of distribution of threading dislocations (TDs) is characterized. The comparison of lattice strain of the material from each processing stage is conducted by both HRXRD and SXRCT.Enlarged contrast of screw and edge types of threading dislocations (TDs) on X-ray topographs after homoepitaxial growth is observed and likely due to interaction with point defects. X-ray topographs reveal ion implantation does not change the distribution of dislocations in the wafer. Strain and tilt maps derived from X-ray rocking curve topographs also show that annealing leads to an improvement in lattice bending levels. These results will be discussed with their implications for further processing into devices.

(Invited) The Dualism between Adatom and Vacancy-Based Single Crystal Growth Models

In homoepitaxial crystal growth, four basic growth morphologies (idealized growth modes) have been established that describe the deposition of atoms on single crystal surfaces: step-flow, layer-by-layer, mound formation, and random/self-affine growth. Mound formation leads to nano-scale surface patterning. However, the formation of (nano)-islands, patterns, and roughness occurs also during ion bombardment, electrochemical etching and oxidation/reduction cycling. Here we show, in analogy to many particle/anti-particle formalisms in physics, the existence of the dualism between individual adatom- and single vacancy-growth modes. We predict that all standard adatom growth modes do exist also in their counter, vacancy version. For the particular case of mound formation, we derive the theoretical equations and show the inverse similarity of the solution. We furthermore treat simultaneous growth by adatoms and vacancies, and derive the analytical solution of the growth shape evolution of the mounds [1]. Applying repeated oxidation-reduction cycles (ORCs) to a Pt(111) surface, we even present an experimental verification, in which both adatom and vacancy mound formation is active simultaneously [2, 3] leading to the roughening. These cycles are comparable to the switching ON/OFF of electrolyzers and fuel cells and the resulting mound formation is eventually responsible for the degradation of the electrode making a large-scale introduction of renewable, hydrogen technology economically less feasible. The theoretically predicted mound shape nicely fits the experimental observation [4]. [1] M.J. Rost, L. Jacobse, and M.T.M. Koper, Nature Communications, 10, 5233, (2019) [2] L. Jacobse, Y.-F. Huang, M.T.M. Koper, and M.J. Rost, Nature Materials, 17 (3), 277, (2018). [3] Movie: https://youtu.be/xSpRcsgxq3Q [4] Movie: https://www.youtube.com/watch?v=xpN_mswrar8 Figure 1

Generation of dislocations from scratches on GaN formed during wafer fabrication and dislocation reactions during homoepitaxial growth

Dislocation generation from scratches induced on a bare GaN wafer during the wafer-fabrication process was investigated via multi-photon excitation photoluminescence (MPPL). The scratch was detected as a faint dark contrast by MPPL but had no accompanying dark dislocation loops that expanded on both sides of the scratch in the GaN wafer. The acceptable quality level for the wafer-fabrication process was determined. Dislocations generated from the scratch elongated to the surface with the repetition of the dislocation reaction. The repetition of the dislocation reaction results in the variation of dislocation types ( a , c , and c + a ). The dislocation structures formed after the dislocation reaction appeared to both decrease as well as increase the dislocation energy. The reactions that appeared to increase the dislocation energy could primarily be attributed to the reaction of threading and half-loop dislocations.

Surface Morphology and Microstructure Evolution of Single Crystal Diamond during Different Homoepitaxial Growth Stages.

Homoepitaxial growth of step-flow single crystal diamond was performed by microwave plasma chemical vapor deposition system on high-pressure high-temperature diamond substrate. A coarse surface morphology with isolated particles was firstly deposited on diamond substrate as an interlayer under hillock growth model. Then, the growth model was changed to step-flow growth model for growing step-flow single crystal diamond layer on this hillock interlayer. Furthermore, the surface morphology evolution, cross-section and surface microstructure, and crystal quality of grown diamond were evaluated by scanning electron microscopy, high-resolution transmission electron microcopy, and Raman and photoluminescence spectroscopy. It was found that the surface morphology varied with deposition time under step-flow growth parameters. The cross-section topography exhibited obvious inhomogeneity in crystal structure. Additionally, the diamond growth mechanism from the microscopic point of view was revealed to illustrate the morphological and structural evolution.

Multifunctional Pd/MOFs@MOFs Confined Core-Shell Catalysts with Wrinkled Surface for Selective Catalysis.

Process intensification, targeting the maximization of spatial-temporal productivity utilizing minimum energy and resources has always been the constant trends especially in chemical industry. In this regard, tandem reactions that are able to perform a multi-step reaction in a single pot by eliminating costly separation steps have been viewed as a typical paradigm. However, a spatial isolation of varied active sites with a controlled manner in a single catalyst to avoid deactivation and work synergistically is a challenging problem yet sometimes being overlooked. In this work, a spatial base-metal core-shell structured catalyst with wrinkled surface was successfully fabricated by a direct homoepitaxial growth method in an acid/water system, which exhibited increased hydrophobicity, exposure of active sites and significantly improved product selectivity towards one-pot Knoevenagel condensation-hydrogenation tandem reaction compared with the uncoated catalyst. Meanwhile, the catalytic performance was largely retained and the structural stability was maintained even after successive 8 cycles, which shows great promise for industrial applications.

Machine learning predictions of surface migration barriers in nucleation and non-equilibrium growth

Machine learning is playing an increasing role in the discovery of new materials and may also facilitate the search for optimum growth conditions for crystals and thin films. Here, we perform kinetic Monte-Carlo simulations of sub-monolayer growth. We consider a generic homoepitaxial growth scenario that covers a wide range of conditions with different diffusion barriers (0.4–0.55 eV) and lateral binding energies (0.1–0.4 eV). These simulations are used as a training data set for a convolutional neural network that can predict diffusion barriers and binding energies. Specifically, a single Monte-Carlo image of the morphology is sufficient to determine the energy barriers with an accuracy of approximately 10 meV and the neural network is tolerant to images with noise and lower than atomic-scale resolution. We believe this new machine learning method will be useful for fundamental studies of growth kinetics and growth optimization through better knowledge of microscopic parameters.

Influence of the facet trace region in 4H-SiC substrate on the glide and propagation behaviors of basal plane dislocations in 4H-SiC homoepitaxial layers

The influence of the facet trace region in the 4H-SiC substrate on the glide and propagation behaviors of basal plane dislocations (BPDs) in a 4H-SiC homoepitaxial layer was investigated using x-ray topography, high-resolution x-ray diffraction, and micro-Raman scattering spectroscopy. The facet trace region in the substrate, which has a higher nitrogen doping concentration than the other regions in the substrate, is of great interest since it could influence the glide and propagation behaviors of BPDs during 4H-SiC homoepitaxial growth through enhanced nitrogen doping concentration in the region. It was found that the epitaxial layer grown on the facet trace region in the substrate significantly suppressed glide motion of BPDs and exhibited a reduced conversion probability of BPDs to threading edge dislocations during the homoepitaxial growth process. Based on these results, the mechanisms that the epilayer grown on a substrate region with a slightly higher nitrogen concentration showed significantly different glide and propagation behaviors of BPDs are discussed.