Lateral Growth Process Research Articles

Ion implantation induced nucleation and epitaxial growth of high-quality AlN

AlN materials have a wide range of applications in the fields of optoelectronic, power electronic, and radio frequency. However, the significant lattice mismatch and thermal mismatch between heteroepitaxial AlN and its substrate lead to a high threading dislocation (TD) density, thereby degrading the performance of device. In this work, we introduce a novel, cost-effective, and stable approach to epitaxially growing AlN. We inject different doses of nitrogen ions into nano patterned sapphire substrates, and then deposit the AlN layers by using metal-organic chemical vapor deposition. Ultraviolet light-emitting diode (UV-LED) with a luminescence wavelength of 395 nm is fabricated on it, and the optoelectronic properties are evaluated. Compared with the sample prepared by the traditional method, the sample injected with N ions at a dose of 1×10<sup>13</sup> cm<sup>–2</sup> exhibits an 82% reduction in screw TD density, the lowest surface roughness, and a 52% increase in photoluminescence intensity. It can be seen that appropriate dose of N ion implantation can promote the lateral growth and merging process in AlN heteroepitaxy. This is due to the fact that the process of implantation of N ions can suppress the tilt and twist of the nucleation islands, effectively reducing the density of TDs in AlN. Furthermore, in comparison with the controlled LED, the LED prepared on the high quality AlN template increases 63.8% and 61.7% in light output power and wall plug efficiency, respectively. The observed enhancement in device performance is attributed to the TD density of the epitaxial layer decreasing, which effectively reduces the nonradiative recombination centers. In summary, this study indicates that the ion implantation can significantly improve the quality of epitaxial AlN, thereby facilitating the development of high-performance AlN-based UV-LEDs.

Synthesis of Lead-Free Cs2AgBiX6 (X = Cl, Br, I) Double Perovskite Nanoplatelets and Their Application in CO2 Photocatalytic Reduction.

Morphology control represents an important strategy for the development of functional nanomaterials and has yet to be achieved in the case of promising lead-free double perovskite materials so far. In this work, high-quality Cs2AgBiX6 (X = Cl, Br, I) two-dimensional nanoplatelets were synthesized through a newly developed synthetic procedure. By analyzing the optical, morphological, and structural evolutions of the samples during synthesis, we elucidated that the growth mechanism of lead-free double perovskite nanoplatelets followed a lateral growth process from mono-octahedral-layer (half-unit-cell in thickness) cluster-based nanosheets to multilayer (three to four unit cells in thickness) nanoplatelets. Furthermore, we demonstrated that Cs2AgBiBr6 nanoplatelets possess a better performance in photocatalytic CO2 reduction compared with their nanocube counterpart. Our work demonstrates the first example with two-dimensional morphology of this important class of lead-free perovskite materials, shedding light on the synthetic manipulation and the application integration of such promising materials.

Lateral growth of xenon hydrate films on mica

<abstract> <p>In this paper, we report an <italic>in situ</italic> optical microscopy study of lateral growth of xenon (Xe) hydrate thin films on mica at sub-zero temperatures. The interactions between a solid surface and water molecules can strongly affect the alignment of water molecules and induce ice-like ordered structures within the water layer at the water-surface interface. Mica was chosen as a model surface to study the surface effect of hydrophilic sheet silicates on the lateral growth of Xe hydrate films. Under the experimental conditions, the lateral growth of Xe hydrate films was measured to be at an average rapid rate of ~200 μm/s and 400 μm/s under two different pressures of Xe. Mass transfer estimation of the Xe-water system revealed that the increasing trend of lateral film growth rates followed the increase in the net mass flux and aqueous solubility of Xe. However, as the supercooling temperature increased, the trend of lateral film growth rates attained a plateau region where little change in the rate was observed. This unique feature in the lateral film growth trend, the fast lateral growth kinetics, and the short induction time for hydrate film growth hinted at the assistance of the mica surface to aid the lateral growth process of Xe hydrate films at low Xe mass flux and at a low degree of subcooling. A mechanism based on the reported structured water layer at the interface on mica was proposed to rationalize a postulated surface-promotional effect of mica on the nucleation and lateral growth kinetics of Xe hydrate films.</p> </abstract>

Direct Visualization of Atomic-Scale Graphene Growth on Cu through Environmental Transmission Electron Microscopy.

The functionalities of two-dimensional (2D) materials are solely determined by their perfect single-layer lattice or precisely stacking of multiple lattice planes, which is predominately determined during their growth process. Although the growth of graphene has been successfully achieved on different substrates with a large area up to millimeters, direct visualization of atomic-scale graphene growth in real time still lacks, which is vital to decipher atomistic mechanisms of graphene growth. Here, we employ aberration-corrected environmental transmission electron microscopy (AC-ETEM) to visualize the nucleation and growth of graphene at the atomic scale in real time. We find a unique lateral epitaxial growth process of graphene on Cu edges under the CO2 atmosphere with a ledge-flow process. The nucleation of graphene nuclei from amorphous carbon atoms also has been found to proceed with a gradual ordering of in-plane carbon atoms. The coalescence of smaller graphene nanoislands to form large ones is thermodynamically favored, and the evolution of atomic structures at grain boundaries is also revealed in great details. These atomic insights obtained from real-time observations can provide direct evidence for the growth mechanisms of graphene, which can be extended to other 2D materials.

Stress evolution in AlN growth on nano-patterned sapphire substrates

The stress evolution behavior of AlN grown on nano-patterned substrates (NPSSs) has been investigated. It is found that there are two sources of the tensile stress for AlN grown on NPSSs. One originates from the coalescence of grain islands of the AlN nucleation layer, and then the voids provide a channel for the gradual release of the tensile stress to nearly stress-free state accompanied by the lateral growth process of the AlN columns on the mesas. The other originates from the contacting of adjacent columns to complete the coalescence process, which is responsible for the residual tensile stress in the top AlN epilayer after completing the coalescence. This understanding of the stress evolution is certainly of great significance in AlN-based material and devices.

Controllable synthesis of millimeter-size single crystal WS2

Two-dimensional transition metal dichalcogenides (TMDs) have attracted much attention due to their unique structure and novel physical properties. Although much progress has been achieved in recent years, it is still a great challenge to synthesize TMDs single crystals with large size controllable. In this paper, we report a controllable method to synthesize single crystalline triangular WS2 with millimeter-scale in length by modulating nucleation and lateral growth process. The monolayer WS2 triangles with edge lengths larger than 1.7 mm were successfully grown on sapphire substrates by using this method. First principle calculation reveals that higher charge density and binding energy on WS2/sapphire interfaces result in the lateral growth to enlarge the size of the triangles on sapphire. On SiO2/Si, however, the triangles appear vertical growth with a size of 200 μm in length. FET transistor based on the triangles on SiO2/Si was fabricated. The on/off ratio of the device could approach to 103, and the field-effect mobility is measured approximately 11 cm2/V·s. The method in this work possibly paves a new way to the growth of WS2 and other TMDs single crystals with large domain size.

Role of the TMG flow rate on the GaN layer properties grown by MOVPE on (hkl) GaAs substrates

The role of the TMG flow rate on the properties of the GaN layer grown by MOVPE on (001) and (11n)/n=2,3 GaAs substrates were investigated. The surface morphology, crystalline quality and optical property were found to be strongly dependent on the TMG flow rate. As the latter decreased to 16 μmol/min, in-situ reflectance measurements showed a constant signal. This is attributed to the enhanced coalescence process, which resulted in the improvement of the surface morphology. A high TMG flow rate of 40 μmol/min sccm promoted predominantly vertical growth and resulted in the formation of a three-dimensional island. The lowest YL intensity and FWHM values of near band edge emission were obtained for GaN layers grown on (001) GaAs substrate with a TMG flow rate of 16 μmol/min, indicating an improvement of the optical properties of the GaN layer. This improvement is attributed to the coalescence process at the initial growth stage of GaN and the lateral growth process. All these behaviors were always observable whatever the used substrates. Depth resolved-CL showed that a mechanism of phase transformation in response to changing the substrate orientations.

Role of dislocations and carrier concentration in limiting the electron mobility of InN films grown by plasma assisted molecular beam epitaxy

We report the molecular beam epitaxy growth of device quality InN films on GaN epilayer and nano-wall network (NWN) templates deposited on c-sapphire by varying the film thickness up to 1 μm. The careful experiments are directed towards obtaining high mobility InN layers having a low band gap with improved crystal quality. The dislocation density is quantified by using high resolution X-ray diffraction rocking curve broadening values of symmetric and asymmetric reflections, respectively. We observe that the dislocation density of the InN films grown on GaN NWN is less than that of the films grown on the GaN epilayer. This is attributed to the nanoepitaxial lateral overlayer growth (ELOG) process, where the presence of voids at the interface of InN/GaN NWN prevents the propagation of dislocation lines into the InN epilayers, thereby causing less defects in the overgrown InN films. Thus, this new adaptation of the nano-ELOG growth process enables us to prepare InN layers with high electron mobility. The obtained electron mobility of 2121 cm2/Vs for 1 μm thick InN/GaN NWN is comparable with the literature values of similar thickness InN films. Furthermore, in order to understand the reasons that limit electron mobility, the charge neutrality condition is employed to study the variation of electron mobility as a function of dislocation density and carrier concentration. Overall, this study provides a route to attaining improved crystal quality and electronic properties of InN films.

Lateral growth of single-crystal Ge on insulating substrate using amorphous Si seed by rapid melting growth

A rapid melting growth of Ge on insulating substrate was developed using amorphous Si seed. Spontaneous nucleation process and lateral growth process occurred at different annealing temperature. Single-crystal Ge stripes on the insulator substrate were obtained as the Ge stripe was dominated by the lateral growth process along the stripes. Different single-crystal Ge stripe has different orientation. No preferential orientation was observed. Spatial gradient of solidification temperature along the Ge stripes induced by Si–Ge mixing in seeding region is the key to cause lateral growth of Ge stripes. Saturation of Si concentration along the Ge stripes at higher annealing temperature was observed, which was explained by limited Si volume in the seeding region.

Threading dislocation annihilation in the GaN layer on cone patterned sapphire substrate

The microstructure of an epilayer structure for the blue light-emitting diode grown on a cone patterned sapphire substrate was characterized by high-resolution X-ray diffraction, atomic force microscopy and transmission electron microscopy (TEM). Cross-sectional TEM revealed that most of the dislocations, which originated from planar region, propagated laterally toward the cone region during the lateral growth process. This change of the propagation direction prevented the dislocations from penetrate the epitaxy film and thus principally led to a drastic reduction in the threading dislocation density in GaN films. Particularly, we proposed that the six {11‾01} semipolar facets play a very important role during the bending process.

Temperature dependence of a‐plane GaN low angle incidence microchannel epitaxy by ammonia‐based metal‐organic molecular beam epitaxy

AbstractThe growth temperature dependence of a‐plane GaN produced by low angle incidence microchannel epitaxy using NH3‐based metal‐organic molecular beam epitaxy was studied. It was found that the width of the laterally grown region increased with temperature. This was because at low temperatures, {10‐12} side facets were formed, which suppressed the lateral growth process by giving rise to inter‐surface diffusion of Ga adatoms from the side to the top of the growing layer. These facets also caused the lateral growth front to assume a zigzag shape. The formation mechanism of the facets can be understood in terms of the Mullin‐Sekerka instability, by which minute periodic undulations gradually increase with growth time when their period is larger than a certain critical value, which increases with growth temperature. Defects in the epitaxial layers were also studied using transmission electron microscopy. Although the defect density was found to be very low in the laterally grown layer itself, a very large number of dislocations and stacking faults were observed both in the template layer and in the epitaxial regions above the openings. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and Characterization of Vertically Aligned Nonpolar [11̅00] Orientation ZnO Nanostructures on (100) γ-LiAlO2 Substrate

In this work, we demonstrate the capability of controlling the crystallographic orientation of ZnO nanostructure arrays grown along nonpolar [11̅00] orientation. The Au catalyst was used to initiate and guide the growth of ZnO nanostructures on (100) γ-LiAlO2 substrate. The morphology, structure, and optical properties of the as-synthesized ZnO nanostructures were characterized by field emission scanning electron microscopy, X-ray diffraction, field emission transmission electron microscope, monochromatic cathodoluminescence image, and photoluminescence spectroscopy. The ZnO nanostructure arrays exhibited special shape and were aligned vertically on the (100) γ-LiAlO2 substrate. A cooperative of Au-catalyzed VLS vertebral column growth along [11̅00] orientation, zinc-self-catalyzed VLS growth along [0001], and ZnO VS lateral expansion growth process was proposed for the special ZnO nanostructures.

Growth of InAs/InAsSb heterostructured nanowires

We report the growth of InAs/InAs1−xSbx single and double heterostructured nanowires by Au-assisted chemical beam epitaxy. The InAs1−xSbx nanowire segments have been characterized in a wide range of antimony compositions. Significant lateral growth is observed at intermediate compositions (x ∼ 0.5), and the nucleation and step-flow mechanism leading to this lateral growth has been identified and described. Additionally, CuPt ordering of the alloy has been observed with high resolution transmission electron microscopy, and it is correlated to the lateral growth process. We also show that it is possible to regrow InAs above the InAsSb alloy segment, at least up to an intermediate antimony composition. Such double heterostructures might find applications both as mid-infrared detectors and as building blocks of electronic devices taking advantage of the outstanding electronic and thermal properties of antimonide compound semiconductors.

Dynamics Study on Morphological Stabilities of Cellular Crystal Lateral Wall

The lateral wall stabilities during the growing process of cellular crystal in the melt were studied in this article. The dynamics equation of cylindrical solid-liquid interface morphological stabilities in melt was first derived, and then the expression of criterion for cylindrical solid-liquid interface morphological stabilities was defined. The effect of the shape factor, solid radius, and other relevant factors on the morphological stabilities was analyzed. Also, the critical shape factor and critical growth rate for keeping the stabilities of the interface were determined. The phenomenon during the lateral growth process of δ-phase cellular crystal in carbon steel was observed under a high-temperature confocal scanning laser microscope (HTCSLM), which was used to verify the theoretical analysis and calculated results. The results indicate that the shape factor is beneficial to improving the stabilities of the cellular crystal lateral wall. During the increase process of the cellular crystal radius, however, there is a certain value of the cellular crystal radius, which induces the shape factor to reduce stabilities of the cellular crystal lateral wall rapidly. Even if the other conditions are unchanged, the shape of the cellular crystal may also cause the cellular crystal lateral wall to lose its stabilities. There are two critical growth rates to keep the cellular crystal lateral wall growing stably under the conditions of this research. For the Fe-0.15 pct C-0.8 pct Mn alloy, these two critical growth rates are 10−4 and 10 cm/s orders of magnitude, respectively. The difference between them is more than 105 times, so the slow critical growth rate conforms to the actual critical growth rate. The radius of the cellular crystal is the main influencing factor of lateral wall stabilities. The bigger the radius of the cellular crystal is, the worse the stabilities of the lateral wall are. That is also one of the reasons that the fine cellular crystal can survive during a certain period. The results of the theoretical analysis about stabilities of the cellular crystal lateral wall agree well with the lateral growth phenomena of δ phase cellular crystal in carbon steel observed by a HTCSLM. The theoretically calculated results of the radial critical growth rates are coincident with the experimental results.

Growth and Microstructure of Epitaxial Ti<SUB>3</SUB>SiC<SUB>2</SUB> Contact Layers on SiC

Growth and microstructure of ternary Ti3SiC2 compound layers on 4H-SiC, which play am important role in formation of TiAl-based ohmic contacts to p-type SiC, were investigated in this study. The Ti3SiC2 layer was fabricated by deposition of Ti/Al contacts (where a slash ‘‘/’’ indicates the deposition sequence) on the 4H-SiC(0001) substrate and subsequent rapid thermal anneal at 1000 � C in ultra high vacuum. After annealing, reaction products and microstructure of the Ti3SiC2 layer were investigated by X ray diffraction analysis and transmission electron microscopy observations in order to understand the growth processes of the Ti3SiC2 layer and determination of the Ti3SiC2/4H-SiC interface structure. The Ti3SiC2 layers with hexagonal plate shape were observed to grow epitaxially on the SiC(0001) surface by anisotropic lateral growth process. The interface was found to have a hetero-epitaxial orientation relationship of ð0001ÞTSC== ð0001ÞS and ½0� 1� TSC== ½0� 1� S where TSC and S represent Ti3SiC2 and 4H-SiC, respectively, and have well-defined ledge-terrace structures with low density of misfit dislocations due to an extremely low lattice mismatch of 0.4% between Ti3SiC2 and 4H-SiC. [doi:10.2320/matertrans.MC200831]

Model of Lateral Growth Stage during Reactive Phase Formation

Lateral growth of intermediate phase during reactive diffusion was analyzed. Proposed model is based on the assumption that the main driving force of the lateral growth process is the chemical one (proportional to composition gradient along the interface). Asymmetric case of phase formation taking into account the curvature of all three interfaces at the triple joint is considered.

Time resolved x-ray reflectivity study of interfacial reactions inCu∕Mgthin films during heat treatment

We present an in-situ time-resolved synchrotron x-ray reflectivity (XRR) analysis of the thermal stability of Cu/Mg/Cu trilayers during heating ramps up to 300 deg. C at 2 deg. C/min. We demonstrate that under some simplifying assumptions the temporal evolution of XRR scans can be used to follow the kinetics of formation of the CuMg{sub 2} intermetallic phase. The simultaneous refinement of selected parameters of 70 reflectivity scans measured during the heat treatment permits an accurate analysis with respect to the as-deposited state. A gradual damping of the long period Kiessig fringes of the trilayer structure is observed upon heating up to 190 deg. C. Above this temperature the XRR is reminiscent of a single thin film of CuMg{sub 2}. The evolution of interface interdiffusion and/or roughness and thickness of the initial layers allowed to identify a differentiated nucleation and lateral growth process of the intermetallic CuMg{sub 2} phase depending on the type of interface, Cu on Mg and Mg on Cu. These results are compared to experimental measurements obtained from differential scanning calorimetry.

Double-Pulsed Green Laser Annealing Tbchnologies

The advanced lateral crystal growth (ALCG) process developed with the double-pulsed green laser annealing system enabled Si grains to be grown laterally and continuously through a step scan of a line beam in the same way as conventional excimer laser annealing (ELA). The field effect mobility of n-channel ALCG-SiTFTs for a current parallel to grain boundaries reaches a high level of 600 cm2/Vs and the strong temperature dependence of the mobility is close to that of single crystal MOS transistors. The 10μm-wide ultra fine beams up to 75 mm in length for the next generation p-SiTFT and up to 150 mm in length for OLED, applied to massproduction machines, were developed by using the beam delivery optics system in conjunction with the optical technique spatially combining multiple laser beams.

The Crystallization Mechanism of Poly-Si Thin Film Using High-power Nd:YAG Laser with Gaussian Beam Profile

AbstractThis paper studies the poly-Si crystallization mechanism under the high power (200 W) Nd:YAG solid state pulsed laser annealing system. It is found that the Gaussian-distributed laser beam profile successfully produce large super lateral growth process window. The devices in the SLG process window exhibit field-effect mobility around 250 cm2/V.s and the threshold voltage lower than 1 V. The influence of a-Si film thickness and the laser scan pitch on the process window is also carefully investigated.

Growth kinetics of an athermal martensitic transformation by time-resolved optical diffraction from a Ni63AI37(001) surface

The vertical and lateral growth process of single martensitic bands on the (001) surface of a Ni 63 Al 37 single crystal was investigated using time-resolved diffraction of He-Ne laser light. Our extended kinephotometric setup provided spatial information through an analysis of the Fraunhofer pattern created by diffraction from the surface relief, while temporal resolution was achieved with a fast-response photodiode. On continuous cooling through the martensitic phase transition at a rate of 10 K/min, discontinuous changes in the diffraction pattern occurred on time scales ranging from 100 microseconds up to some tens of milliseconds. Each change in the pattern corresponded to a burst-like upheaval of the relief by a few hundred nanometers. The bands were fully developed within 150 - 250 ms and reached final heights of about 1.5 μm.