Lateral Overgrowth Research Articles

Factors Affecting Lateral Overgrowth in Operatively Treated Lateral Condyle Fractures in Children.

The most frequent sequelae of pediatric lateral condyle fractures is lateral condyle overgrowth (LCO). The purpose of our study was to investigate LCO in relation to age, quality of reduction, type of fixation, and fracture displacement. We retrospectively analyzed operatively treated lateral condyle fractures in children. The percent change in interepicondylar width (IEW) ((final - initial)/ initial x 100) was used to quantify LCO. IEW was measured from the medial and lateral epicondyles of the distal humerus, using the AP radiographs taken at admission (initial) and follow-up visits (final). The Song classification was used to classify fractures. Fixation was classified as pins, screws or both. The quality of reduction was defined as anatomic or nonanatomic (>2mm of displacement). Patients were stratified into mild (0% to 10% overgrowth), moderate (10% to 20% overgrowth), and severe (>20% overgrowth) subgroups for further analysis. Two hundred one patients were included in the study with an average time between initial and final radiograph measurements of 11.32 weeks. There was an average 11.84 %LCO. Using multivariable analysis, three variables demonstrated significant, independent associations with %LCO: age, race, and quality of reduction. Increasing age remained inversely associated with %LCO. Compared with White patients, Black and Asian patients had significantly greater %LCO. Patients with nonanatomic reductions had a significantly greater %LCO compared with anatomic reductions. When patients were stratified into mild, moderate, and severe groups, age in the mild group, nonanatomic reduction in the moderate group, and race in the severe group were found to be independently associated with increased %LCO using multivariable analysis. The amount of LCO was found to be related to nonanatomic reduction, younger age, and Black and Asian race. Interestingly, it was not related to the amount of initial displacement or type of hardware used. To date, this is the largest study investigating LCO in surgically treated lateral condyle fractures. Level III-retrospective cohort study.

The quality of epitaxial lateral overgrown diamond on substrate with laser-cut holes of varying shapes and side orientations

This study analyzes dislocation densities, stress levels, and crystal quality in the epitaxial lateral overgrowth (ELO) areas of CVD epitaxial layer on substrate with laser-cut holes of varying shapes and side orientations. It revealed that the shape and side orientation of holes on the substrate significantly impacted the quality of the ELO layers. Rectangular holes with the 〈100〉 crystal orientation on the sides favor improving the quality of CVD diamond. Under optimized conditions, the tensile stress of the ELO areas decreased as well as the dislocation density reduced to 3 × 105 cm−2, approximately 20 times lower than the non-ELO areas.

Nanocrystalline Diamond Lateral Overgrowth for High Thermal Conductivity Contact to Unseeded Diamond Surface

We demonstrate diamond lateral overgrowth as a way of increasing the thermal conductivity of thin layers of diamond. The technique can be used as a way of growing diamond on top of semiconductors, creating a thin layer of high thermal conductivity diamond in direct contact with semiconductors and allowing for the encasement of GaN in high thermal conductivity diamond.As we move to higher and higher power densities, the requirements for heat removal become extreme. The best passive way to remove heat from a semiconductor is to have a high thermal conductivity heat spreader near the heat source. Having diamond under the substrate is good. Having diamond under the epi is better and having diamond on top and bottom of the epi is better still.As-grown thin layers of diamond on non-diamond substrates have nano-diamond seeds as the starting material. The diamond thermal conductivity is a function of the grain size (Especially for small grain material) [1]. If we can increase the grain of the diamond near the junction, we can increase the thermal conductivity near the junction and more efficiently spread the heat away from the source before rejecting it into the surrounding material.In the experiment, we start with a bare silicon wafer seeded with nano-diamond seeds then grow about one micron of diamond. We coat it with a few nanometers of SiN. Then pattern the SiN layer with 2μm wide features to facilitate the coalescence of LOG-NCD over the SiN. Then we grow a 2μm thick microwave-plasma CVD NCD film (800W, 15Torr, 750°C, 0.3% CH4/H2) over the patterned SiN film initiating directly from the exposed areas of the host NCD. The diamond growth does not initiate on the patterned silicon nitride without seeds. The exposed diamond acts as a nucleating center initiating the diamond regrowth. The regrown diamond spreads from the diamond crystals exposed from the first growth. The edge crystals closest to the SiN patterned area expand over the silicon nitride forming diamond conformal to the SiN surface. This creates large crystals over the unseeded area. Figure 1 is a transmission electron microscope (TEM) image of the sample. The TEM, the image can be split into two regions. The left has no patterning, the called-out grain is 100nm wide. The right is patterned, and the diamond grains are between 1,000 to 2,000nm wide.We measured the thermal conductivity of the diamond on this samples using the TDTR method. This method uses a laser many times larger in diameter than the thickness of the film. As such, we probe the out-of-plane thermal conductivity. The initial diamond growth near the silicon had an average thermal conductivity of 100W/mK. We measured the second micron of growth without patterns to have Tc of 130W/mK. The diamond directly above the patterns had Tc of 260W/mK with grains 10X larger than the un-patterned diamond.Since the diamond grains are columnar, the difference in thermal conductivity between the patterned and un-patterned diamonds was 2X. Lateral measurements would likely show even larger changes in thermal conductivity. With grain sizes of 100 nm to 250 nm (as is the case with seeded diamond), the in-plane thermal conductivity will be dominated by the quality of the grain/grain interfaces and the lateral grain size dimensions rather than for the quality of the lattice. [1] We used lateral overgrowth to increase the grains to microns rather than 100s of nm. This means that we move into a regime where thermal conductivity is dominated by the quality of the diamond in the grains rather than the grain boundaries. As such the thermal conductivity is increased and can be further improved by improving the crystal quality - a parameter which is controlled by the diamond growth conditions. Typically, samples grown with more than 1% methane / hydrogen ratio show lower thermal conductivity [2]. However higher concentrations are important to establish the initial diamond film without damage to the underlying semiconductor. Here, the lateral overgrowth and methane concentration can be balanced to achieve both high thermal conductivity and low damage to the underlying substrate.

Geometrically Controlled Microscale Patterning and Epitaxial Lateral Overgrowth of Nitrogen-Polar GaN.

In this Letter, we report on a novel two-step epitaxial growth technique that enables a significant improvement of the crystal quality of nitrogen-polar GaN. The starting material is grown on 4° vicinal sapphire substrates by metal-organic vapor-phase epitaxy, with an initial high-temperature sapphire nitridation to control polarity. The material is then converted to a regular array of hexagonal pyramids by wet-etching in a KOH solution and subsequently regrown to coalesce the pyramids back into a smooth layer of improved crystal quality. The key points that enable this technique are the control of the array geometry, obtained by exploiting the anisotropic behavior of the wet-etch step, and the use of regrowth conditions that preserve the orientation of the pyramids' sidewalls. In contrast, growth conditions that cause an excessive expansion of the residual (0001̅) facets on the pyramids' tops cause the onset of a very rough surface morphology upon full coalescence. An X-ray diffraction study confirms the reduction of the threading dislocation density as the regrowth step develops. The analysis of the relative position of the 0002̅ GaN peak, with respect to the 0006 sapphire peak, reveals a macroscopic tilt of the pyramids, probably induced by the large off-axis substrate orientation. This tilt correlates very well with an anomalous broadening of the 0002̅ diffraction peaks at the beginning of the regrowth step.

InGaN/GaN Hybrid‐Nanostructure Light Emitting Diodes with Emission Wavelength Green and Beyond

Three sets of InGaN/GaN nanowire (NW) heterostructures are grown on Si(111) substrates under different growth conditions. A quasi‐two‐dimensional p‐GaN layer is grown on top of those structures using the epitaxial lateral overgrowth (ELOG) technique. Finally, the light‐emitting diodes (LED) are fabricated using these hybrid nanostructures following standard fabrication techniques. Electroluminescence (EL) measurement confirmed the emission wavelengths of 530.0 nm (green), 608.3 nm (orange), and 632.5 nm (red). The knee voltages of the devices are estimated to be in the range of 2.18–2.89 V, with higher knee voltages for samples emitting lower wavelengths. Further analysis of forward bias electrical characteristics suggests the dominance of tunneling current and an increase in the defect density in the heterostructures emitting higher wavelengths.

Interfacial improvement of diamond through epitaxial lateral overgrowth with periodic Ir/SiO2/Ir stripe mask

Epitaxial lateral overgrowth (ELO) of diamond film with SiO2 stripe mask has been carried out through microwave plasma chemical vapor deposition systems. To solve the peel-off of SiO2, this study evaluates different kinds of metal buffer layers and chooses Ir as the optimal metal. The effects of the interface feature of two types of stripe masks (Ir/SiO2 and Ir/SiO2/Ir stripes) on the internal stress status and the fluorescence properties are characterized. The optical image confirms that the diamond emerges in the interval of stripes at the initial growth stage and then forms a continuous film with smooth surface and step-flow mode after 37 h lateral overgrowth. Photoluminescence (PL) mapping demonstrates that the SiO2 mask is etched by H2 plasma and results in a high SiV− intensity, especially above the mask. The Ir cap layer on the Ir/SiO2 mask surface is effective in preventing the SiO2 from being etched in the plasma atmosphere, greatly alleviating the PL intensity of the SiV− color center compared with that of the Ir/SiO2 mask. In addition, the Ir cap layer can suppress the stress in the epitaxial layer. The findings of this study can advance the existing research on ELO technology and be potentially applied to vacancy-related color centers.

Large Area Epitaxial Lateral Overgrowth of Semipolar (11¯$1 \left(\right. \macr \left.\right)$01) GaN Stripes on Patterned Si Substrates Prepared using Maskless Lithography

Selective area growth and epitaxial lateral overgrowth (ELOG) of semipolar (101) GaN stripes are demonstrated on a trench patterned vicinal (001) Si substrate fabricated by a maskless photolithography‐based process. High precision alignment enables selective mask formation to one sidewall of the trench. Selective area growth of GaN stripes is conducted from the (111) plane sidewall of Si, and ELOG region reaches ≈13 μm. The ELOG GaN crystal is dislocation‐free at most areas. The semipolar GaN stripes with atomically flat surface morphology are uniformly obtained. Light‐emitting diode structures with InGaN/GaN multiple quantum wells are grown on the 13‐μm ELOG (101) GaN stripes and a single photoluminescence emission peaked at 485 nm is obtained, suggesting potential for the cost‐effective semipolar micro light‐emitting diode fabrication technologies.

Nanocrystalline Diamond Lateral Overgrowth for High Thermal Conductivity Contact to Unseeded Diamond Surface

We demonstrate unseeded lateral overgrowth of nanocrystalline diamond as a way of increasing the thermal conductivity of thin layers of diamond. The technique can be used as a way of growing diamond on top of semiconductors, creating a thin layer of high thermal conductivity diamond in direct contact with semiconductors and allowing for the encasement of GaN in high thermal conductivity diamond.

Controlled formation of three-dimensional cavities during lateral epitaxial growth

Epitaxial growth is a fundamental step required to create devices for the semiconductor industry, enabling different materials to be combined in layers with precise control of strain and defect structure. Patterning the growth substrate with a mask before performing epitaxial growth offers additional degrees of freedom to engineer the structure and hence function of the semiconductor device. Here, we demonstrate that conditions exist where such epitaxial lateral overgrowth can produce complex, three-dimensional structures that incorporate cavities of deterministic size. We grow germanium on silicon substrates patterned with a dielectric mask and show that fully-enclosed cavities can be created through an unexpected self-assembly process that is controlled by surface diffusion and surface energy minimization. The result is confined cavities enclosed by single crystalline Ge, with size and position tunable through the initial mask pattern. We present a model to account for the observed cavity symmetry, pinch-off and subsequent evolution, reflecting the dominant role of surface energy. Since dielectric mask patterning and epitaxial growth are compatible with conventional device processing steps, we suggest that this mechanism provides a strategy for developing electronic and photonic functionalities.

Decomposition of the anisotropic strain in 3D-structure GaN layers using Raman spectroscopy

Strain engineering for gallium nitride has been studied by many researchers to improve the performance of various devices (i.e., light-emitting diodes, laser diodes, power devices, high electron mobility transistors, and so on). Further miniaturization of gallium nitride devices will clearly continue in the future, and therefore an accurate understanding of the strain state in the devices is essential. However, a measurement technique for axially resolved evaluation of the strain in microareas has not yet been established. In this study, we revealed that the anisotropic strain state induced in c-plane growth gallium nitride is linked to the split state of Raman peaks, which were measured with z(xx)z¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z(xx)\\overline{z }$$\\end{document} and z(yx)z¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z(yx)\\overline{z }$$\\end{document} polarized configurations. The anisotropic strain state in c-plane gallium nitride was induced in the 3D-structure by epitaxial lateral overgrowth, which enabled successful performance of our work. This result allowed us to axially decompose the strain in c-plane gallium nitride through Raman spectroscopy and establish a measurement technique for axially resolving the strain. This measurement technique is feasible using a conventional Raman spectrometer. Furthermore, the method was indicated to be applicable to all wurtzite-type crystals, including gallium nitride, silicon carbide, and aluminum nitride. Our work provides a new perspective for understanding the complex strain state in microareas for wurtzite materials. Comprehending the strain state, which strongly affects device performance, will help promote the research and development of III-V semiconductor devices.

Microstructural and spectroscopic analysis of epitaxial lateral overgrowth GaN via the self-decomposing hexagonal graphene mask

The use of two-dimensional material like graphene to alleviate lattice mismatch has been an effective way to realize high-quality GaN on heterogeneous substrates. The lack of hanging bonds on the graphene surface provides a new attempt for epitaxial lateral overgrowth (ELOG). In this study, a hexagonal graphene mask was used for the growth of GaN, the graphene mask disappeared during the GaN growth process, but GaN still maintained the ELOG mode, and the threading dislocation density was significantly reduced. Raman and PL spectra demonstrated the stress relaxation in ELOG GaN and showed a stress relaxation of 0.157 GPa at the interface between the substrate and ELOG GaN. This study demonstrates the feasibility and advantages of graphene masks for nitrides and extends the research on stress relaxation of ELOG GaN using a graphene mask.

Comparative analysis of selective area grown Ga- and N-polar InGaN/GaN nanowires for quantum emitters

In this paper, we report the molecular beam epitaxy-grown InGaN-quantum disks embedded within selective area epitaxy of GaN nanowires with both Ga- and N-polarities. A detailed comparative analysis of these two types of nanostructures is also provided. Compared to Ga-polar nanowires, N-polar nanowires are found to exhibit a higher vertical growth rate, flatter top, and reduced lateral overgrowth. InGaN quantum disk-related optical emission is observed from nanowires with both polarities; however, the N-polar structures inherently emit at longer wavelengths due to higher indium incorporation. Considering that N-polar nanowires offer more compelling geometry control compared to Ga-polar ones, we focus on the theoretical analysis of only N-polar structures to realize high-performance quantum emitters. A single nanowire-level analysis was performed, and the effects of nanowire diameter, taper length, and angle on guided modes, light extraction, and far-field emission were investigated. These findings highlight the importance of tailoring nanowire geometry and eventually optimizing the growth processes of III-nitride nanostructures.

Controlled Crystallinity of a Sn-Doped α-Ga2O3 Epilayer Using Rapidly Annealed Double Buffer Layers.

Double buffer layers composed of (AlxGa1-x)2O3/Ga2O3 structures were employed to grow a Sn-doped α-Ga2O3 epitaxial thin film on a sapphire substrate using mist chemical vapor deposition. The insertion of double buffer layers improved the crystal quality of the upper-grown Sn-doped α-Ga2O3 thin films by blocking dislocation generated by the substrates. Rapid thermal annealing was conducted for the double buffer layers at phase transition temperatures of 700-800 °C. The slight mixing of κ and β phases further improved the crystallinity of the grown Sn-Ga2O3 thin film through local lateral overgrowth. The electron mobility of the Sn-Ga2O3 thin films was also significantly improved due to the smoothened interface and the diffusion of Al. Therefore, rapid thermal annealing with the double buffer layer proved advantageous in achieving strong electrical properties for Ga2O3 semiconductor devices within a shorter processing time.

Influence of pressure on AlN thick films prepared by epitaxial lateral overgrowth through hydride vapor phase epitaxy

Smooth and crack-free (0002) AlN thick films (∼30 μm) were epitaxially grown on trench-patterned AlN/sapphire templates through epitaxial lateral overgrowth (ELO) using hydride vapor phase epitaxy.

The limit of anisotropic epitaxial lateral overgrowth in heteroepitaxial systems

The separation of Ge and Si by an electrically isolating dielectric layer is essential to yield high efficiency for optical telecommunication applications and electronic applications such as Ge MOSFETs. Ge epitaxial lateral overgrowth (ELOG) is a promising approach to achieve Ge on Si separated by a thin dielectric layer. However, a general understanding of the anisotropic dynamics of ELOG Ge on Si is limited, which prevents its wide adoption. In this paper, we report how the orientation and width of the dielectric layer controls the ELOG. A competitive ELOG from perpendicular directions on a dielectric strip leads to a rapid growth along the long axis of the dielectric layer, or a mixed coalescence from perpendicular directions yielding various Ge confined configurations at the Ge/dielectric-layer interface. Especially, an angle of 7.5° between dielectric-layer and Si [110] axis shows the most pronounced unidirectional ELOG. ELOG disappears as the width of the dielectric mask exceeds 5.0 μm. The results reported here provide a general framework for ELOG of semiconductor materials.

Nucleation Selectivity and Lateral Coalescence of GaAs over Graphene on Ge(111).

We use epitaxial lateral overgrowth (ELO) to produce semimetallic graphene nanostructures embedded in a semiconducting GaAs matrix for potential applications in plasmonics, THz generation and detection, and tunnel junctions in multijunction solar cells. We show that (1) the combination of low sticking coefficient and fast surface diffusion on graphene enhances nucleation selectivity at exposed regions of the substrate and (2) high growth temperatures favor efficient lateral overgrowth, coalescence, and planarization of epitaxial GaAs films over the graphene nanostructures. Our work provides a more complete understanding of ELO using graphene masks, as opposed to more conventional dielectric masks, and enables new types of metal/semiconductor nanocomposites.

Epitaxial Lateral Overgrowth of Wafer‐Scale Heteroepitaxial Diamond for Quantum Applications

Wafer‐scale heteroepitaxial diamond thin films demonstrate multiple advantages for a further development of integrated optical and quantum devices based on impurity–vacancy color centers. The main obstacle here is a high structural defect density characteristic for heteroepitaxial epilayers. In this work, technological methods of stress control, NV formation, and defect density reduction in diamond epilayers, which are based on principles of epitaxial lateral overgrowth (ELO) are reported on. Herein, material and quantum properties of NV‐doped diamond thin films obtained by patterned nucleation growth and by ELO of microstructured epilayers, are compared. It is demonstrated that a combination of both methods might have a significant potential for the wafer‐scale production of heteroepitaxial diamond for quantum devices.

Editors’ Choice—Structural, Electrical, and Luminescent Properties of Orthorhombic κ-Ga2O3 Grown by Epitaxial Lateral Overgrowth

The properties of orthorhombic κ-Ga2O3 films grown by Epitaxial Lateral Overgrowth (ELOG) were studied by Scanning Transmission Electron Microscopy (STEM), X-ray diffraction, capacitance-voltage profiling, Microcathodoluminescence (MCL) spectroscopy and imaging. ELOG mask was formed by deposition of SiO2 stripes on TiO2 buffer prepared on basal plane sapphire, with the stripes going along the [110] direction of sapphire. κ-Ga2O3 ELOG growth was performed using Halide Vapor Phase Epitaxy (HVPE), with ELOG wing of the structure formed by lateral overgrowth over the 20 μm-wide SiO2 stripes, while growth in between the stripes proceeded initially by vertical growth in the 5-μm-wide windows. TEM analysis showed that the material in the windows comprised 120o rotational nanodomains typical of κ-Ga2O3, while, in the wing regions, the material was single-domain monocrystalline. The films were conducting, with the net donor density close to 1013 cm−3. The data suggested the material in the windows have much higher resistance than in the wings. MCL spectra and imaging revealed much higher density of nonradiative recombination centers in the windows than in the wings.

Remote epitaxial interaction through graphene.

The concept of remote epitaxy involves a two-dimensional van der Waals layer covering the substrate surface, which still enable adatoms to follow the atomic motif of the underlying substrate. The mode of growth must be carefully defined as defects, e.g., pinholes, in two-dimensional materials can allow direct epitaxy from the substrate, which, in combination with lateral epitaxial overgrowth, could also form an epilayer. Here, we show several unique cases that can only be observed for remote epitaxy, distinguishable from other two-dimensional material-based epitaxy mechanisms. We first grow BaTiO3 on patterned graphene to establish a condition for minimizing epitaxial lateral overgrowth. By observing entire nanometer-scale nuclei grown aligned to the substrate on pinhole-free graphene confirmed by high-resolution scanning transmission electron microscopy, we visually confirm that remote epitaxy is operative at the atomic scale. Macroscopically, we also show variations in the density of GaN microcrystal arrays that depend on the ionicity of substrates and the number of graphene layers.

Properties of κ‐Ga2O3 Prepared by Epitaxial Lateral Overgrowth

AbstractThe structural and electrical properties of undoped and Sn doped κ‐Ga2O3 layers grown by epitaxial lateral overgrowth on TiO2/sapphire substrates using stripe and point masks show that the crystalline structure of the films can be greatly improved relative to conventional planar growth. The undoped films are semi‐insulating, with the Fermi level pinned near EC‐0.7 eV, and deep electron traps at EC‐0.5 eV and EC‐0.3 eV are detectable in thermally stimulated current and photoinduced current transient spectra measurements. Low concentration Sn doping results in net donor concentrations of ≈ 1013 cm−3, and deep trap spectra determined by electron traps at EC‐0.5 eV, and deep acceptors with an optical ionization threshold near 2 and 3.1 eV. Treatment of the samples in hydrogen plasma at 330 °C increases the donor density near the surface to ≈ 1019 cm−3. Such samples show strong persistent photocapacitance and photoconductivity, indicating the possible DX‐like character of the centers involved. For thin (5 µm) κ‐Ga2O3 films grown on GaN/sapphire templates, p‐type‐like behavior is unexpectedly observed in electrical properties and we discuss the possible formation of a 2D hole gas at the κ‐Ga2O3/GaN interface.