Surface Of Sapphire Substrate Research Articles

Oriented lateral growth of two-dimensional materials on c-plane sapphire.

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) represent the ultimate thickness for scaling down channel materials. They provide a tantalizing solution to push the limit of semiconductor technology nodes in the sub-1 nm range. One key challenge with 2D semiconducting TMD channel materials is to achieve large-scale batch growth on insulating substrates of single crystals with spatial homogeneity and compelling electrical properties. Recent studies have claimed the epitaxy growth of wafer-scale, single-crystal 2D TMDs on a c-plane sapphire substrate with deliberately engineered off-cut angles. It has been postulated that exposed step edges break the energy degeneracy of nucleation and thus drive the seamless stitching of mono-oriented flakes. Here we show that a more dominant factor should be considered: in particular, the interaction of 2D TMD grains with the exposed oxygen-aluminium atomic plane establishes an energy-minimized 2D TMD-sapphire configuration. Reconstructing the surfaces of c-plane sapphire substrates to only a single type of atomic plane (plane symmetry) already guarantees the single-crystal epitaxy of monolayer TMDs without the aid of step edges. Electrical results evidence the structural uniformity of the monolayers. Our findings elucidate a long-standing question that curbs the wafer-scale batch epitaxy of 2D TMD single crystals-an important step towards using 2D materials for future electronics. Experiments extended to perovskite materials also support the argument that the interaction with sapphire atomic surfaces is more dominant than step-edge docking.

Formation of submicron relief structures on the surface of sapphire substrates

An analysis of technologies that allow creating microrelief structures on the surface of sapphire substrates has been carried out. It is shown that the most effective method of forming relief structures with submicron dimensions is ion beam etching through a protective mask formed by photolithography. The main problems in creating a microrelief on the surface of sapphire substrates are the removal of static electric charge in the process of ion beam etching of the substrates, as well as obtaining a protective mask with windows of specified sizes, through which etching of the sapphire substrate is performed.

Defect Location in Laterally Aligned Tin Oxide Nanowires: The Role of Growth Direction, Interface Dimensionality, and Catalyst

Laterally aligned SnO2 nanowires, which exhibit planar growth along crystallographically defined directions of a sapphire substrate surface, are superior for bio- and gas-sensing applications. Little is known about their cross-sectional geometry and the defect distribution within the nanowire cross section, although this substantially determines the electronic properties of the nanowires. In this study, SnO2 nanowires were grown on r-plane sapphire substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal the highly oriented growth of the SnO2 nanowires toward the substrate edges. High-resolution transmission electron microscopy (HRTEM) of the NW cross section and strain mapping allowed for analyzing the crystallographic alignment of the SnO2 NW to the sapphire substrate and the defect distribution within the SnO2 nanowire cross section. These techniques revealed a defect-free SnO2–Al2O3 interface and a high alignment of the SnO2 NW lattice toward the sapphire substrate along the NW width. The determined high defect density close to the nanowire surface will be discussed in comparison to freestanding SnO2 nanowires and SnO2 thin films on sapphire substrates considering the differences in the growth direction and the interface dimensionality.

Tribochemical mechanisms of abrasives for SiC and sapphire substrates in nanoscale polishing.

Strong acid, alkali, or active chemicals are generally employed in chemical mechanical polishing (CMP) slurry for the ultra-precision machining of semiconductor substrates, obstructing further improvement in machining accuracy and reduction in damaged layers. Understanding the material removal behavior of abrasives, which combines mechanical and chemical actions during nanoscale abrasive polishing, poses a significant challenge. In this study, the interfacial interaction mechanisms between abrasives and substrates during nanoscale polishing with only deionized water used as coolant were analyzed by utilizing concerned experiments and molecular dynamics (MD) simulations. The results showed that ultra-smooth SiC and sapphire substrate surfaces only with damage layer thicknesses of 2.06 nm and 0.76 nm were obtained by employing diamond abrasive and alumina abrasive, respectively. Tribochemical reactions could occur on substrate surfaces under the repeated interfacial fiction of fine abrasives without any chemical reagents during nanoscale polishing. The tribochemical reactions mainly depended on the chemical compatibility between the abrasives and substrates when the material removal size of abrasives was limited to nanoscale, not abrasive hardness. Furthermore, a new method of abrasive selection is proposed and widely applied in the ultra-precision polishing of semiconductor substrates, which could not only improve removal efficiency but also ensure good surface quality.

Dislocation reduction mechanism os GaN films on vicinal sapphire substrates

<sec>GaN materials are widely used in optoelectronic devices, high-power devices and high-frequency microwave devices because of their excellent characteristics, such as wide frequency band, high breakdown electric field, high thermal conductivity, and direct band gap. Owing to the large lattice mismatch and thermal mismatch brought by the heterogeneous epitaxy of GaN material, the GaN epitaxial layer will produce a great many dislocations in the growth process, resulting in the poor crystal quality of GaN material and the difficulty in further improving the device performance. Therefore, researchers have proposed the use of vicinal substrate to reduce the dislocation density of GaN material, but the dislocation annihilation mechanism in GaN film on vicinal substrate has not been sufficiently studied. Therefore, in this paper, GaN thin films are grown on vicinal sapphire substrates at different angles by using metal organic chemical vapor deposition technique. Atomic force microscope, high resolution X-ray diffractometer, photoluminescence testing, and transmission electron microscopy are used to analyze in detail the effects of vicinal substrates on GaN materials. The use of vicinal substrates can significantly reduce the dislocation density of GaN materials, but lead to degradation of their surface morphology morphologies. And the larger the substrate vicinal angle, the lower the dislocation density of the sample is. The dislocation density of the sample with a 5º bevel cut on the substrate is reduced by about one-third compared to that of the sample with a flat substrate. The special dislocation termination on the mitered substrate is observed by transmission electron microscopy, which is one of the main reasons for the reducing the dislocation density on the mitered substrate. The step merging on the vicinal sapphire substrate surface leads to both transverse growth and longitudinal growth of GaN in the growth process. The transverse growth region blocks the dislocations, resulting in an abrupt interruption of the dislocations during propagation, which in turn reduces the dislocation density.</sec><sec>Based on the above phenomena, a model of GaN growth on vicinal substrate is proposed to explain the reason why the quality of GaN crystal can be improved by vicinal substrate.</sec>

Solid-phase epitaxy of a CuAlO2 template on c-Al2O3 for delafossite growth

Thin-film growth of ABO2 delafossites has recently attracted significant attention due to its attractive transport properties and potential applications. A fundamental requirement for achieving high-quality thin films is the availability of lattice matching substrates and chemical compatibility. However, there are still many obstacles to achieving high-quality thin films. Here, we report a process to further engineer a template ABO2 delafossite structure by solid-phase epitaxy of CuAlO2 on the surface of a commercial sapphire substrate, which offers a promising route to growing high-quality epitaxial thin films. The starting reagents involve a layer of polycrystalline Cu2O deposited on a c-Al2O3 substrate by pulsed laser deposition (PLD). Subsequent thermal treatment activates a solid-state interface reaction between the film and substrate, producing a CuAlO2 thin film. The reaction temperature and dwell time parameters were optimized in this study to prepare a phase diagram for CuAlO2 samples without phase impurities. This method provides an essential stepping-stone toward the approachability of a lattice matching template (i.e., substrate-buffer layer) for ABO2 heterostructures. An example of successful epitaxial growth of highly conducting PdCrO2 is also demonstrated by using a CuAlO2 buffer layer.

The influence of TMGa pre-flow time and amount as surfactant on the structural and optical properties of AlN epilayer

AIN is used as a template layer for deep UV (DUV) emitter and detector applications, because of its wide bandgap and high thermal conductivity. In this study, trimethylgallium (TMGa) source is used as surfactant to improve crystal quality and decrease dislocation density (DD) of AlN layers grown on sapphire (Al2O3) substrate surfaces by Metal Organic Vapor Phase Epitaxy (MOVPE) system. TMGa pre-flow time and pre-flow amount that TMGa pre-flow to the nucleation stage are the subjects of two distinct optimization studies. The structural and optical properties of grown AIN are examined by a high resolution X-ray diffractometer (HR-XRD), Raman spectroscopy, and UV–Vis–NIR spectrophotometer, respectively. TMGa pre-flow time and TMGa pre-flow amount determined to obtain high crystal quality AlN epilayers are 2 s and 0.446 × 10−5 mol/min, respectively. HR-XRD investigation of these growths yields FWHM values of 159/2718 arcsec and 201/1550 arcsec for the ω (002) and ω (102) scans, respectively.

Cathodoluminescent Analysis of Sapphire Surface Etching Processes in a Medium-Energy Electron Beam.

Sapphire crystals are widely used in optics and optoelectronics. In this regard, it is important to study the stability of crystals under external influence and the possibility of modifying their surfaces by external influence. This work presents the results of studying the processes of the action of an electron beam with an average energy of 70 keV or less under vacuum conditions on the surfaces of sapphire substrates of various orientations. The effect of etching a sapphire surface by an electron beam in vacuum at room temperature was discovered. The highest etching rate was observed for A-plane sapphire (the average pit etching rate was 10−6 µm3/s). It was shown that the rate of etching of a sapphire surface increased many times over when gold is deposited. An in situ method for studying the process of etching a sapphire surface using cathodoluminescence analysis was considered. Possible mechanisms of sapphire etching by a beam of bombarding electrons were considered. The results obtained could be important in solving the problem of the stability of sapphire windows used in various conditions, including outer space. In addition, the proposed method of metal-stimulated etching of a sapphire surface can be widely used in patterned sapphire substrate (PSS) technology and further forming low-dislocation light-emitting structures on them.

The study of spray impact on the heated sapphire plate

The process of the liquid spray impact on the heated surface is studied experimentally using the IR-transparent sapphire plate method. The spatiotemporal distribution of the temperature field on the sapphire substrate surface during impacting spray is received. The obtained experimental data are an important step in a study of the local characteristics of heat transfer in the areas of the contact lines during liquid spray impact on the heated surface. Further, the local heat fluxes and heat transfer coefficients will be determined by solving the problem of thermal conductivity in the sapphire substrate.

Optimal Selection of Backside Roughing Parameters of High-Value Components Using Abrasive Jet Processing

This paper mainly presents a set of new Sapphire Backside Roughing technology. Presently, the associated Sapphire Backside Roughing technology is still concentrated on chemical etching, as its yield rate and efficiency are often limited by lattice structures, and the derived chemical waste fluid after etching is most likely to cause ecological contamination. In this research, refined abrasive jet processing technology is adopted, and in the meantime, the Taguchi experiment design method is taken for detailed experimental planning. Through processing parameter conditions and abrasive selection and development, proper surface roughing and processing uniformity are obtained so as to improve the various weak points of the abovementioned traditional etching effectively. It is discovered that abrasive blasting processing technology is, respectively, combined with wax-coated #1000 SiC particles and wax-coated #800 Zirconium particles to process the sapphire substrate with initial surface roughness 0.8–0.9 μmRa from the experiment. A 1.1–1.2 μmRa surface roughness effect can be achieved about two minutes later. The experimental results show that the actual degree of sapphire substrate surface roughing obtained in the AJM process depends on the gas pressure, impact angle, wax-coated abrasives, and additives. The new Sapphire Backside Roughing technology has high flexibility, which not only meets the requirements for sapphire surface roughing specification but can also effectively reduce the sapphire substrate roughing time and related cost.

Epitaxial GaN films with ultralow threading dislocation densities grown on an SiO2-masked patterned sapphire substrate

This letter reports on epitaxial GaN layers with ultralow threading dislocation (TD) densities grown by metal organic chemical vapor deposition on SiO2-masked patterned sapphire substrates (SMPSSs). The patterning employs periodic micro-scale SiO2 cone-shaped features on thin sapphire pedestals surrounded by flat c-plane sapphire substrate surfaces. Cross-sectional transmission electron microscopy results demonstrate that GaN films grown on SMPSSs provide an ultralow TD density of 8.5 × 106 cm−2. A GaN LED structure grown on SMPSS-based GaN film provides an optical output power that is 130% greater than that obtained for an equivalent LED structure grown on a standard PSS-based GaN film.

Crystalline GaAs Thin Film Growth on a c-Plane Sapphire Substrate

Crystalline zinc blende GaAs has been grown on a trigonal c-plane sapphire substrate by molecular beam epitaxy. The initial stage of GaAs thin film growth has been investigated extensively in this paper. When grown on c-plane sapphire, it takes (111) crystal orientation with twinning as a major problem. Direct growth of GaAs on sapphire results in three-dimensional GaAs islands, almost 50% twin volume, and a weak in-plane correlation with the substrate. Introducing a thin AlAs nucleation layer results in complete wetting of the substrate, better in-plane correlation with the substrate, and reduced twinning to 16%. Further, we investigated the effect of growth temperature, pregrowth sapphire substrate surface treatment, and in-situ annealing on the quality of the GaAs epilayer. We have been able to reduce the twin volume below 2% and an X-ray diffraction rocking curve line width to 223 arcsec. A good quality GaAs on sapphire can result in the implementation of microwave photonic functionality on a photonic chip.

Fabrication of sapphire rib waveguides using a femtosecond laser

We demonstrate a method for fabricating sapphire rib waveguides with femtosecond laser micromachining technology. Finite difference beam propagation method (FD-BPM) is applied to design sapphire rib waveguides. We explore the process of etching on a sapphire substrate surface via direct laser ablation. Rib waveguides that satisfies the dimensions of our design were fabricated. Actual light propagation performance is tested, and with the cut-back method, the insertion loss of 2.9±0.5 dB/cm is measured.

Pursuit of single domain ZnTe layers on sapphire substrates

ZnTe layers were grown on various orientation surfaces of sapphire substrates, namely c-, a-, r-, and S-planes. Single domain dominant layers were achieved by carefully controlling the substrate orientation and introducing the thin buffer layer. The substrate surfaces were annealed at approximately 1000 °C to achieve an atomically smooth surface with step-terrace structures. Single domain layers were achieved by employing the step-terrace structured substrates. A nanofacet structure of the substrate surface consisting of the r-plane and the S-plane was obtained by annealing the m-plane substrate surface. Nucleation of ZnTe occurred along the nanofacet. It was confirmed that preferential nucleation of ZnTe on the S-plane of the nanofacet took place. Nitrogen doping of the ZnTe layer was performed, with the doping efficiency confirmed as being as good as ZnTe layers prepared on GaAs substrates. This is another indication of the high crystal quality for the prepared ZnTe layer.

High signal/noise ratio deep UV detector with maximum response at 230 nm based on mix-phase MgZnO deposited under high laser energy condition

A Mix-phase MgZnO thin film was fabricated on the c-plane sapphire substrate (Mg0.4Zn0.6O target) under high laser energy density condition by the PLD method. The internal quantum efficiency of the detector based on the mix-phase MgZnO thin film at 230 nm deep UV light reached 86% at 40 V bias voltage. And the Iuv(230 nm)/Idark ratio of the MgZnO detector reached 864 at 40 V bias voltage, which is mainly caused by both the higher internal gain of the detector at deep UV light and its smaller Idark. The high internal gain of the detector is mainly due to the higher density of interfaces between the different structure of MgZnO grains in the mix-phase MgZnO thin film, which is caused by the higher laser energy density deposition condition certified by contrast experiments. The small Idark of the detector is mainly caused by the higher barriers in the mix-phase MgZnO thin film and more cubic MgZnO in the mix-phase MgZnO thin film, and higher laser energy density deposition condition and O-rich c-plane sapphire substrate surface are key factors, which also agree with the contrast experiments results. So when the mix-phase MgZnO thin film that is constituted by both a small number of narrower band gap hexagonal MgZnO and a large number of wide band gap cubic MgZnO is used in the deep UV detector, and the difference in band gaps between different structures of MgZnO is relatively higher, a higher signal/noise ratio of the device at 230 nm deep UV light is gained, which is meaningful for developing high-performance deep UV detection technology.

Study on the finishing capability and abrasives-sapphire interaction in dry chemo-mechanical-grinding (CMG) process

Chemo-mechanical-grinding (CMG) is a fixed abrasive process by integrating both chemical reaction and mechanical grinding. This paper targets on studying the finishing ability of dry CMG processes for mono-crystal sapphire and understanding the underlying abrasives-sapphire interaction. The experiment results suggest that dry CMG processes by applying either Cr2O3 or SiO2 are able to produce sapphire substrate with an excellent surface quality and subsurface integrity, meanwhile, maintain the geometric accuracy. The underlying abrasives-sapphire interaction termed as solid phase reaction is demonstrated by X-ray photoelectron spectroscope (XPS) analysis. It is suggested that Cr2O3 abrasives is more chemically active against sapphire (Al2O3) when compared with SiO2 abrasives. Combined with a higher mechanical effect provided by Cr2O3 abrasives, the finishing efficiency of Cr2O3 abrasives is almost 2 times higher than traditional SiO2 abrasives. The subsurface integrity characterization by using Raman microscope and transmission electron microscope reveals that Cr2O3 abrasives introduces a shallow damage layer (about 100 nm) on the top surface of sapphire substrate since the chemical effect is not sufficient enough to meet the balance with mechanical effect. With a better mechanical-chemical balance achieved by SiO2 abrasives, a damage free subsurface is obtained. Therefore, besides of traditional SiO2 abrasives, Cr2O3 abrasives is suggested to be another potential candidate for finishing sapphire substrate.

Experimental research on the changing process of sapphire substrate surface shape and surface roughness in double-sided lapping

Experimental research on the changing process of sapphire substrate surface shape and surface roughness in double-sided lapping

Epitaxy of CdTe on sapphire substrates with titanium buffer layers

The formation of a developed electrical relief on the sapphire substrate surface is investigated. A technique is proposed for introducing Ti4+ impurity atoms into the sapphire crystal lattice by depositing titanium layers with a thickness of about 5 nm and their annealing in air (oxidizing atmosphere) to a temperature of 1400°C. It is shown that this preliminary treatment of the sapphire substrate surface results in epitaxial growth of (111) СdTe films parallel to the sapphire (0001) plane at a temperature of 350°C.

Silanization of Sapphire Surfaces for Optical Sensing Applications.

Well-characterized silane layers are essential for optimized attachment of (bio)molecules enabling reliable chem/biosensor performance. Herein, binding properties and orientation of 3-mercaptopropyltrimethoxysilane layers at crystalline sapphire (0001) surfaces were determined by water contact angle measurements, infrared reflection absorption spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Infrared reflection absorption spectroscopy measurements suggest an almost perpendicular arrangement of the MPTMS molecules to the substrate surface. Adhesion force studies between a silicon nitride AFM tip and modified sapphire, gold, and silicon dioxide substrates were investigated by peak force tapping atomic force microscopy and used to define the silane binding properties on these surfaces. As expected, the Al-O-Si bond was determined to be responsible for the layer formation at the sapphire substrate surface.

Facile synthesis of various epitaxial and textured polymorphs of vanadium oxide thin films on the (0006)-surface of sapphire substrates

Wafer-scale epitaxial and textured polymorphs of vanadium oxide thin films on low-cost sapphire substrates enable real applications.