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In this study, three samples of GaN/AlInN/AlN/Al2O3 high electron mobility (HEMT) structures are investigated with high resolution X-ray diffraction (HR-XRD) technique. Peak positions and peak broadenings are used in calculations, gained from rocking curves. Structural quality is determined from symmetric and asymmetric peak planes. Mosaic defects such as treadening dilocations (TDs), tilt and twist angles, lateral and vertical crystallite lengths are determined by using Williamson Hall (WH) method. In addition to these, surface morphology is also investigated by atomic force microscopy (AFM). It is noticed that crystal quality of epitaxial layers decrease in the order of samples C, B and A. Al compositions for samples A, B and C are found as %87.4, %86.6 and %86.4, respectively by using Vegard’s law.

Fabrication of the surface micro-texture on the C-plane sapphire is undertaken by a 355 nm Ultraviolet (UV) pulsed laser. The surface micro textures of sapphire with different laser scanning line spacing ranging from 10 μm to 100 μm are obtained, where the selection range of scanning line spacing is controlled in the range of the groove width and plasma width to obtain a surface of high Peak-Valley (PV) value. A reasonable processing order is proposed to manufacture different types of surface micro-textures on sapphire by laser ablation trajectory regulation. In the multiple-passes laser ablation of sapphire by the UV nanosecond pulsed laser, the scanning lines in each direction is treated as once scanning. On this basis, the multiple processing can be carried out to avoid the influence of the subsequent scanning on the machined groove. In addition, the effect of different scanning line spacing on the PV value is quantified and different types of surface micro-textures on sapphire, including the squares, the rhombuses and the hexagons, are successfully fabricated, which can be applied in the friction reduction or anti-reflection field.

Optical frequency domain reflectometry measurements in internally clad single crystal sapphire fiber have received attention in recent years due to their high temperature distributed sensing potential. As work with these fibers has proceeded, there have been some inconsistencies in the results. Deeper investigation and testing has identified two critical considerations for the proper functioning of these fibers. First, users must address the propagation of multimode light along the outer surface of the fiber. By observing the far-field image of an internally clad sapphire fiber when adding index matching fluid to the outer fiber surface, we demonstrate the effects of removing the higher order modes from these fibers. The addition of index matching fluid resulted in nearly single mode performance where multimode performance was previously observed. Second, users must address the effect that coupling the fiber to the interrogator via silica based fiber has on the internally clad sapphire fibers performance. Direct fusion splicing of silica to sapphire, as has been used in the recent work with these fibers, has a mode filtering effect which can be beneficial towards the modal behavior of the fibers. However, in this paper we demonstrate that the splicing can cause a sensing failure due to little or no low order mode light, that is useful for sensing, returning to the detector. The positive results from recent years have demonstrated that optical frequency domain reflectometry sensing performance will be successful in clad sapphire fiber; but only when the considerations described herein are addressed properly.

We demonstrate and compare indium and silicon as secondary cathode material for the analysis of flat, solid alumina and sapphire matrices by direct-current glow discharge mass spectrometry (dc-GDMS). The mask designs and the glow discharge conditions are optimised for signal ratio and absolute intensity. The mask material was found to be a small factor on matrix to mask ratio and signal intensity despite the large difference in properties between indium and silicon. The results indicate that the discharge conditions play the most significant role. The mask material did not appear to affect RSFs. On sapphire with indium, the possible discharge conditions and performance where limited due to a collapse in discharge. This was not the case for silicon, which proves to be a good alternative as secondary cathode material.

The authors would like to thank KAUST Baseline Funds BAS/1/1664-01-01, Competitive Research Grants URF/1/3437-01-01 and URF/1/3771-01-01, and GCC Research Council REP/1/3189-01-01 for their support.

Gallium Oxide (Ga2O3) and Sapphire have been a preferred choice of substrates for fabricating β-Ga2O3 Schottky barrier diodes (SBDs). However, Si (100) substrate with low cost and relatively high thermal conductivity has been explored as a platform in this work for the growth of β-Ga2O3 using the pulsed laser deposition (PLD) technique. X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) results confirm the good crystalline quality and uniformity of the Ga2O3 film, respectively. The roughness (RMS) of 1.44 nm of the film surface is confirmed by the atomic force microscope (AFM) technique. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics are employed for investigating the electrical and interface trap properties of the SBDs. The Schottky barrier height measured at room temperature from I-V and C-V characteristics are 0.78 eV and 1.17 eV, respectively and the ideality factor turns out to be 1.95. The charge transport mechanism of SBD has been investigated using the log-log plot of I-V characteristics. The Schottky metal (Au)/β-Ga2O3 interface trap density (Dit) which is obtained on the order of 10 cm-2 eV-1 using the conventional conductance method. In the energy range of Ec-0.27 eV to Ec-1.57 eV, the density of interface states changes from 3.72×10 eV-1cm-2 to 3.10×10 eV-1cm-2, respectively. The maximum value of Dit is found to be 4.38 ×10 eV-1cm-2 at Ec-0.68 eV. The value of Dit can be further reduced for potential and reliable integration of β-Ga2O3 with Si electronics.

Faraday isolator with composite terbium gallium garnet TGG/sapphire magneto-optical elements that were produced by the surface-activated direct bonding method was created. Thermally induced depolarization and thermal lens for composite elements were investigated experimentally and numerically. The resulting structures operated successfully at a high radiation power, providing an isolation ratio exceeding the classical single element made of TGG by 5 dB and amounted to 34 dB at a laser power of 700 W. The maximum operating power at which the isolation ratio was higher than 30 dB was estimated to be over 2 kW, which is almost 3 times more than in the case of a single TGG.

Sapphire possesses chemically inert and high hardness. Therefore, it is difficult to get idea material removal rate (MRR) and low surface roughness through chemical mechanical polishing (CMP). Ultr...

The results of ellipsometric, x-ray, and spectral studies of In2O3 films deposited by dc-magnetron sputtering on Al2O3 (012) substrates are presented. The experimental data are interpreted in terms of a three-layer model of the fi lm. It is assumed that large particles of the material are formed on the surface of the substrate at the beginning of the deposition process. The size of the crystallites then decreases, and they fill the gaps between the larger particles, after which the film formation goes into the stationary mode. It was shown that there is a transition layer with a band gap of 1.39 eV, a refractive index of ~3, and thickness of 25 nm at the interface between the film and the substrate. The properties of this layer do not depend on the deposition time.

Recently, hexagonal boron nitride (h-BN), an ultra-wide bandgap semiconductor, has attracted considerable attention owing to its excellent properties. In thin films grown on metal catalysts, contamination and damage induced by a transfer process cannot be avoided. Therefore, synthesizing h-BN films on non-catalytic dielectric substrates is desirable for electronic applications. In this study, we demonstrate the direct growth of high-quality h-BN films with a controllable thickness on sapphire substrates by using the pulsed laser deposition (PLD) technique. The effects of the deposition conditions and laser parameters on the growth of the h-BN films are systematically investigated by evaluating their characteristic Raman peaks. Among the various growth parameters studied, the substrate temperature has the greatest influence on the crystalline quality of the h-BN films, and the optimal pressure varies depending on the target-substrate distance. The h-BN film grown under optimal conditions exhibits a narrow Raman line width of ∼30 cm−1, indicating a high crystalline quality. The photodetectors fabricated from the PLD-grown h-BN films exhibit superior deep-ultraviolet detection performance with a large on/off ratio of >104, high photoresponsivity, and a sharp cut-off wavelength of 220 nm. This study presents the possibility of producing high-quality h-BN films by applying PLD on dielectric substrates for optoelectronic applications.

It is indispensable to achieve antireflection and protection of the sapphire (i.e., Al2O3 single crystal) infrared window, especially in extreme environments such as high temperature and high-energ...

Multicomponent oxide (GaxIn1−x)2O3 films are prepared on (0001) sapphire substrates to realize a tunable band-gap by magnetron sputtering technology followed by thermal annealing. The optical properties and band structure evolution over the whole range of compositions in ternary compounds (GaxIn1−x)2O3 are investigated in detail. The X-ray diffraction spectra clearly indicate that (GaxIn1−x)2O3 films with Ga content varying from 0.11 to 0.55 have both cubic and monoclinic structures, and that for films with Ga content higher than 0.74, only the monoclinic structure appears. The transmittance of all films is greater than 86% in the visible range with sharp absorption edges and clear fringes. In addition, a blue shift of ultraviolet absorption edges from 380 to 250 nm is noted with increasing Ga content, indicating increasing band-gap energy from 3.61 to 4.64 eV. The experimental results lay a foundation for the application of transparent conductive compound (GaxIn1−x)2O3 thin films in photoelectric and photovoltaic industry, especially in display, light-emitting diode, and solar cell applications.

Two-dimensional (2D) transition-metal dichalcogenide materials (TMDs) alloys have a wide range of applications in the field of optoelectronics due to their capacity to achieve wide modulation of the band gap with fully tunable compositions. However, it is still a challenge for growing alloys with uniform components and large lateral size due to the random distribution of the crystal nucleus locations. Here, we applied a simple but effective promoter assisted liquid phase chemical vapor deposition (CVD) method, in which the quantity ratio of promoter to metal precursor can be controlled precisely, leading to tiny amounts of transition metal oxide precursors deposition onto the substrates in a highly uniform and reproducible manner, which can effectively control the uniform distribution of element components and nucleation sites. By this method, a series of monolayer Nb1−xWxSe2 alloy films with fully tunable compositions and centimeter scale have been successfully synthesized on sapphire substrates. This controllable approach opens a new way to produce large area and uniform 2D alloy film, which has the potential for the construction of optoelectronic devices with tailored spectral responses.

We report the characteristics of AlN epilayers grown directly on cylindrical-patterned sapphire substrates (CPSS) by hydride vapor-phase epitaxy (HVPE). To evaluate the effect of CPSS, we analyzed the threading dislocation densities (TDDs) of AlN films grown simultaneously on CPSS and flat sapphire substrate (FSS) by transmission electron microscopy (TEM). The corresponding TDD is measured to be 5.69 x 108 cm−2 for the AlN sample grown on the CPSS that is almost an order of magnitude lower than the value of 3.43 × 109 cm−2 on the FSS. The CPSS contributes to reduce the TDs originated from the AlN/sapphire interface via bending the TDs by lateral growth during the coalescence process. In addition, the reduction of direct interface area between AlN and sapphire by CPSS reduce the generation of TDs.

Heteroepitaxy of β-phase gallium oxide (β-Ga2O3) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of (201)-oriented β-Ga2O3 heteroepitaxial thin films were investigated. Unintentionally doped β-Ga2O3 thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward ⟨1120⟩ via metal-organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the β-Ga2O3 thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the β-Ga2O3 films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick β-Ga2O3 thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye-Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of β-Ga2O3 films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the β-Ga2O3 films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the β-Ga2O3/sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown (201)-oriented β-(AlxGa1-x)2O3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(AlxGa1-x)2O3 films exhibit lower thermal conductivities (2.8-4.7 W/m·K) than the β-Ga2O3 thin films. The dominance of the alloy disorder scattering in β-(AlxGa1-x)2O3 is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown β-phase Ga2O3 and (AlxGa1-x)2O3 thin films and lays the groundwork for the thermal modeling and design of β-Ga2O3 electronic and optoelectronic devices.

Optically transparent materials are being found in an ever-increasing array of technological applications within industries, such as automotive and communications. These industries are beginning to realize the importance of implementing surface engineering techniques to enhance the surface properties of materials. On account of the importance of surface engineering, this paper details the use of a relatively inexpensive diode-pumped solid state (DPSS) Nd:YVO4 laser to modify the surfaces of fused silica glass, diamond, and sapphire on a micrometre scale. Using threshold fluence analysis, it was identified that, for this particular laser system, the threshold fluence for diamond and sapphire ranged between 10 Jcm−2 and 35 Jcm−2 for a laser wavelength of 355 nm, dependent on the cumulative effects arising from the number of incident pulses. Through optical microscopy and scanning electron microscopy, it was found that the quality of processing resulting from the Nd:YVO4 laser varied with each of the materials. For fused silica glass, considerable cracking and deformation occurred. For sapphire, good quality features were produced, albeit with the formation of debris, indicating the requirement for post-processing to remove the observed debris. The diamond material gave rise to the best quality results, with extremely well defined micrometre features and minimal debris formation, comparative to alternative techniques such as femtosecond laser surface engineering.

Ultraviolet germicidal irradiation (UVGI) is an effective technique that can sterilize bacteria and viruses by UV light. Far UVC lamps of short wavelengths can prevent infectious diseases because they sterilize while minimizing cell damage in mammals. Here, E. coli inactivation by far UVC light with peak wavelength of 230 nm made of carbon nanotube (CNT) emitters and sapphire anode was studied. The κ-Al2O3 phase of sapphire with a direct band gap of 5.4 eV was excited with CNT-based cold cathode electron beam (C-beam) to generate far UVC light. It was confirmed that the inactivation of E. coli by far UVC light based on the C-beam was reduced by 5 log reduction within 60 s.

A GaN alpha-particle detector of p-i-n structure was fabricated on a sapphire substrate in this article. The intrinsic layer of the detector was isoelectronic Al-doped GaN with the thickness of $10~\mu \text{m}$ . The leakage current of the detector remained below 10 pA when the reverse voltage increased from 0 to 40 V, which proved that it had a better crystal quality than the detector based on undoped i-GaN layer, of which the dark current was 10 nA at −40 V. The carrier concentration derived from the 1/ $C^{2}$ – $V$ curve was $4.96\times 10^{14}$ cm−3, so the i-GaN layer would be fully depleted at −48 V. With the remarkable improvement of electrical properties, the charge collection efficiency (CCE) of the full depleted detector in this article was as high as 99%, while the energy resolution was about 4%. These results reveal the excellent prospect of GaN-on-sapphire for cost-effective alpha-particle detectors.

Blazed gratings are widely used in optical detection devices with the unique property of concentration of light energy to a desired diffraction order. However, traditional substrates for fabricating blazed gratings are easily damaged with the wear and tear in long-term usage under harsh conditions. Here, we propose the fabrication of blazed gratings on sapphire with high mechanical stability by femtosecond laser lithography combined with subsequent reactive ion etching (RIE). Various sapphire blazed gratings with periods from 2 μm to 10 μm and heights from 260 nm to 2 μm were realized to concentrate light energy (wavelengths of 405 nm, 532 nm and 633 nm) to different diffraction orders (1st, 2nd, and 3rd). The results provide great insights for the construction of micro-optical devices that have potential applications under harsh conditions.

Multiphoton microscopy (MPM) including two-photon excited fluorescence (TPEF), second harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS) is an important tool in biology and medicine to explore the dynamics of cells and to investigate tissue structure in living systems and biopsies. However, MPM still suffers from limited applicability due to the integration of highly sophisticated lasers. In this paper, we introduce our triple-modal multicolor MPM platform employing a single direct diode-pumped femtosecond Kerr-lens-mode-locked Ti:sapphire oscillator and acquire simultaneously intrinsic co-registered multicolor TPEF, TPEF, SHG and CARS signals in the backward direction. The complexity and by that the footprint as well the cost of the laser are considerably reduced by the direct diode-pumping scheme. In combination with an Yb fiber amplifier such a laser is suited for biomedical applications allowing for detailed morphologic and molecular spectroscopic in vivo investigation. The optimized emission wavelengths of our Ti:sapphire laser and Yb fiber amplifier provide simultaneous excitation at 805 nm, 1050 nm and 911 nm for multicontrast information from exogenous and endogenous fluorophores. We perform in vivo imaging of C. elegans and visualize metabolic changes in zebrafish larvae to investigate the tumor microenvironment with spectral focusing CARS and multicolor TPEF of green fluorescent protein.

We investigated the structural characteristics and defect states of intrinsic GaN epi-layers in a high power device structures grown on GaN and sapphire substrates by metal–organic chemical vapor deposition (MOCVD). From X-ray diffraction, Raman spectroscopy, and photoluminescence measurements, the structural properties of the GaN epi-structures were improved clearly using GaN substrates. Through optical conductance deep level transient spectroscopy analysis, four traps were observed in all the GaN layers. The activation energies of these traps were 0.93 eV (H1), 0.61 eV (H2), 0.50 eV (H3), and 0.2 eV (H4) above the valance band edge, and their capture cross-sections were 3.41 × 10–14 cm2 (H1), 3.04 × 10–14 cm2 (H2), 1.35 × 10–12 cm2 (H3) and 2.90 × 10–16 cm2 (H4), respectively. The origins of the H4 and H1 traps may be related to gallium vacancy (VGa) and VGa-related defects, and the H2 and H3 traps were from nitrogen vacancy (VN). The total defect density of GaN epi-layers estimated using the space charge limited current method was reduced to 1.18 × 1015 cm−3 on GaN substrates from about 1.52 × 1017 cm−3 on sapphire substrates.

We presented a hybrid sapphire dual-Fabry—Perot- cavities sensor for high temperature and refractive index measurement. A double-sided polished sapphire solid wafer is connected in series with a double-sided parallel sapphire C-ring and a single-sided polished sapphire mirror to form the hybrid Fabry—Perot interferometer. The double-sided polished sapphire solid wafer acts as the first Fabry—Perot cavity for temperature sensing, and the sapphire hollow C-ring cavity constitutes the second Fabry—Perot cavity for measuring the refractive index of external environment medium. The single-sided polished sapphire mirror serves as the most distal reflector. Heterogeneous fiber splicing between sapphire fiber and multimode silica fiber is realized to achieve long-distance transmission of interference signals. A series of high temperature measurement experiments range of room temperature to 1080 °C in an air environment and refractive index measurement experiments in a liquid environment were carried out. Based on the changing rates of corresponding Fabry—Perot cavity optical path difference against refractive index and temperature, we calculated the sensitivities of the sensor. The refractive index and temperature sensitivities were 2.0659 × 105 nm/RIU in the RI range of 1.3330∼1.3741 and 7.837 nm/ °C at 1080 °C.

Paradiso 23 is intensely lyrical. Everything in it is part of a coherent construct both readable in relation to itself alone and also as part of a larger set of themes, images, and narrative strategies. Even by the standards of the Paradiso, it takes place in an atmosphere of exalted rarification and intense dependence on metaphor. Until the final lines there is no hint of earthly troubles, nor are we given the cosmological or theological discourses we have come to expect. The canto is replete with tropes of phonic repetition (alliteration and assonance), with Latinisms, and exclamations—all of which serve to magnify its intensity and stylistic elegance, even while conveying, for most readers, an effect of simplicity. Instead of the customary dialogue between Dante and the souls that he encounters, this canto is given over to spectacle; the only dialogue is between Dante and Beatrice.

Indium gallium nitride (InGaN) based blue light-emitting diodes (LEDs) suffer from insufficient crystal quality and serious efficiency droop in large forward current. In this paper, the InGaN-based blue LEDs are grown on sputtered aluminum nitride (AlN) films to improve the device light power and weaken the efficiency droop. The effects of oxygen flow rate on the sputtering of AlN films on sapphire and device performance of blue LEDs are studied in detail. The mechanism of external quantum efficiency improvement is related to the change of V-pits density in multiple quantum wells. The external quantum efficiency of 66% and 3-V operating voltage are measured at a 40-mA forward current of with the optimal oxygen flow rate of 4 SCCM. [Image: see text]

Single-photon emitters (SPEs) are one of the building blocks in quantum information processing. Here, we report detailed experimental optical properties of the SPEs in aluminum nitride (AlN) films at 10 K. The high-quality AlN films are grown by metal–organic chemical vapor deposition on graphene/sapphire substrates, which can conquer the large lattice and thermal mismatches between the sapphire and AlN. We report the defects in AlN with a relatively high Debye–Waller factor up to ∼29% and near-perfect linear polarization SPEs with a saturation count rate of 1.43 × 10⁶ counts/s. The power-dependent second-order autocorrelation measurements are used to study the transition kinetics, which can be described using a three-level model. The polarization measurements of absorption and emission reveal the optical cycle mechanism, where a particular zero-phonon line may be excited via multiple mechanisms. This work provides some insight into the nature of the optical properties and energy-level structures of AlN defects, which pave the way to integrated on-chip quantum photonics.

Sapphire is an important ceramic material which finds applications in fields such as temperature sensing, optics, electronics, and ceramic bearings. Polishing of sapphire has always been a difficult task for industries and research communities. Hydrodynamic polishing (HDP) is one of the prominent methods used for polishing of hard and profiled surfaces, whereas rigid tool-based methods such as diamond turning, grinding, and honing have many limitations. The HDP process involves deterministic flow of abrasive particles in the slurry between the workpiece surface and a rotating soft tool to obtain the desired surface finish. A novel experimental setup has been fabricated to realize the conformal hydrodynamic nanopolishing on single crystal sapphire cavity. In this study, the experiments were conducted to understand the effect of abrasive particle size, basicity of slurry, and change in temperature of slurry on the polishing of machined sapphire cavity. The effect of the initial surface roughness of the machined cavity on conformal hydrodynamic nanopolishing has also been investigated. A microcrack/pit-free surface has been found after the final polishing of the sapphire cavity. An improvement of 21% is found in surface finish after the final polishing using abrasive particle size of 0.06 µm. Abrasive slurry with higher basicity (pH 13) does not improve the surface finish. By heating the abrasive slurry to a temperature of 70°C–75°C, surface finish improves by ∼26% as compared to improvement of ∼ 21% at room temperature polishing.

Formation of continuous and adherent diamond films on practical substrates presents a formidable challenge due to lack of diamond nucleation sites needed for diamond growth. This problem has been solved through the formation of interfacial Q-carbon layers by nanosecond laser melting of carbon layers in a highly undercooled state and subsequent quenching. The Q-carbon layer provides ready nucleation sites for epitaxial films on planar matching substrates such as sapphire, and polycrystalline films on amorphous substrates such as glass. Each laser pulse converts about a one-cm-square area, which can be repeated with a 100–200 Hz laser to produce potentially 100–200 cm2s-1 of diamond films. This is essentially a low-temperature processing, where substrate stays close to ambient temperature, because the total heat input is quite small. The Q-carbon layer is also responsible for improved adhesion of diamond films on sapphire and glass substrates. It is also argued that the formation of Q-carbon layer is also responsible for efficient diamond nucleation during negatively biased MPCVD diamond depositions.

Owing to the lack of large-diameter and affordable AlN bulk crystals, high-quality AlN films grown on sapphire substrates have been intensively analyzed for the potential applications in optoelectr...

Low dislocation density of α-Ga2O3 grown on conical frustum-patterned sapphire substrate (CF-PSS) has been studied. The threading dislocation propagation path of α-Ga2O3 on CF-PSS was observed., The compound α-Ga2O3 is an ultra-wide-bandgap semiconductor and possesses outstanding properties such as a high breakdown voltage and symmetry compared with other phases. It has been studied for applications in high-performance power devices. However, it is difficult to obtain a high-quality thin films because α-Ga2O3 can only grow heteroepitaxially, which results in residual stress generation owing to lattice mismatch and thermal expansion between the substrate and α-Ga2O3. To overcome this, α-Ga2O3 was grown on a conical frustum-patterned sapphire substrate by halide vapor-phase epitaxy. The surface morphology was crack-free and flat. The α-Ga2O3 grown on a frustum-patterned substrate and a conventional sapphire substrate at 500°C exhibited full-width at half-maxima of 961 and 1539 arcsec, respectively, for 10–12 diffraction. For the former substrate, lateral growth on the pattern and threading dislocation bending towards the pattern suppressed the propagation of threading dislocations generated at the interface, which reduced the threading dislocation propagation to the surface by half compared with that on the latter conventional substrate. The results suggest that conical frustum-patterned sapphire substrates have the potential to produce high-quality α-Ga2O3 epilayers.

The ZnSe single crystal treatment in air environment with linearly polarized Ti/sapphire femtosecond (fs)laser pulses of the energy density of around 0.04-0.05 J/cm2 with central wavelength of 800 nm and the pulse duration of 140 fs at a repetition rate of 1 kHz generates the laser-induced periodic surface structures (LIPSSs). The setup with a cylindrical quartz lens at normal incidence allowed processing a relatively large area of the ZnSe sample in one pass of the laser beam. Morphology analysis of LIPSS by scanning electron microscopy (SEM) and image processing reveals the existence of two periods of around 200.0 nm and 630.0 nm simultaneously. All LIPSSs demonstrate the orientation perpendicular to the laser beam polarization. The possible nature of LIPSS formation on ZnSe single crystal is caused by the synergetic influence of the interference mechanism involving surface plasmon polaritons and hydrodynamic effects of surface morphology modification. The fs-laser-induced changes of carrier concentrations in ZnSe specify obtained periods of high spatial frequency LIPSS. The influence of femtosecond laser processing on luminescent properties of ZnSe single crystal has been studied by an analysis of the photoluminescence (PL) and X-ray luminescence (XRL) spectra of laser-treated and untreated areas in the visible region of spectrum at room and low temperatures. The PL spectra and XRL spectra, as well as temperature dependencies of XRL spectra or thermally stimulated luminescence curves, demonstrate a good correlation for untreated and fs-laser-treated ZnSe surfaces. Specific PL bands related to the extended structural defects do not appear for LIPSS at the ZnSe sample under an excitation of 337 nm (3.68 eV). The Relative intensities and position of separate components of observed luminescence bands after ultrashort laser treatment do not change significantly. Thus, the structural perfection of the ZnSe single crystal surface is preserved.

We show that fast technical fluctuations of microwave signals can be strongly suppressed by cryogenic resonators. The experiments were carried out with sapphire resonators cooled to approximately 6 K at frequencies around 11 GHz. Each sapphire crystal was shaped like a spindle with the rotational and crystal axes aligned within a degree. Noise suppression factors in excess of 50 dB were measured at 10-kHz offset from the carrier. This was achieved by rotating the sapphire spindle and moving the coupling probes relative to its surface. Microwave signals with reduced fast technical fluctuations allow the high-precision tests of fundamental physics, as well as the development of better radars.

The nanoporous (NP) GaN wafers which were fabricated by electrochemical etching (EC) method were used as substrates to deposit Er-doped Ga2O3 epitaxial films by pulsed layer deposition (PLD). The epitaxial relationship between the GaN and Er doped β-Ga2O3 film was Ga2O3 (−201) ‖ GaN (0001) with Ga2O3 [010] ‖ GaN [-12-10]. Compared to the Er doped films on the epi-GaN wafers with the porosity of 0%, ~20% and ~60%, the β-Ga2O3 film deposited on the wafer with a porosity of ~40%, which has an energy bandgap of ~4.89 eV, has the best crystal quality and optoelectronic properties. The performance enhancement should be due to improved crystalline quality as a result of the existence of nanopores in the etched substrates. The excellent properties of Er doped Ga2O3 films indicated that the films have great potential to fabricate Ga2O3 optoelectronic devices.

The reflection and transmission characteristics of edge-cooled single-disk output radio frequency (RF) windows of 95-GHz 100-kW gyrotron were studied. RF characteristics of output windows made off sapphire (rhombohedral, single crystalline), silicon nitride composite, and pyrolytic boron nitride (poly crystalline) (PBN) were compared. At the operating frequency, the return losses of 64.0, 60.0, and 50.0 dB were obtained, respectively, for sapphire, silicon nitride composite, and PBN while the related transmission losses turned to be, respectively, better than −0.01, −0.02, and −0.04 dB. The heat load due to RF power absorption in the disk was least for sapphire and maximum for PBN window. The structural analyses of these RF windows predicted the least deflection and least tensile stress for silicon nitride and PBN windows, respectively. Comparable bandwidths were offered by silicon nitride window (790 MHz) of thickness 1.13 mm and PBN (773 MHz) of thickness 2.19 mm. However, a major safety margin and thus structural integrity was offered by the silicon nitride (factor of safety 30.6) window in comparison to PBN (factor of safety 10.6).

Trends in the behavior of band gaps in short-period superlattices (SLs) composed of CdO and MgO layers were analyzed experimentally and theoretically for several thicknesses of CdO sublayers. The optical properties of the SLs were investigated by means of transmittance measurements at room temperature in the wavelength range 200–700 nm. The direct band gap of {CdO/MgO} SLs were tuned from 2.6 to 6 eV by varying the thickness of CdO from 1 to 12 monolayers while maintaining the same MgO layer thickness of 4 monolayers. Obtained values of direct and indirect band gaps are higher than those theoretically calculated by an ab initio method, but follow the same trend. X-ray measurements confirmed the presence of a rock salt structure in the SLs. Two oriented structures (111 and 100) grown on c- and r-oriented sapphire substrates were obtained. The measured lattice parameters increase with CdO layer thickness, and the experimental data are in agreement with the calculated results. This new kind of SL structure may be suitable for use in visible, UV and deep UV optoelectronics, especially because the energy gap can be precisely controlled over a wide range by modulating the sublayer thickness in the superlattices.

The aim of the study is to understand the effects of NH3 flow rate in the initial part of high temperature (HT) GaN growth on structural and optical characteristics of the HT-GaN layer grown on dome shaped sapphire susbtrate by Metal Organic Chemical Vapor Deposition (MOCVD) system. High resolution x-ray diffraction (HRXRD) and photoluminescence (PL) measurements were performed to characterization the growing GaN epilayer. It is observed that the using of different NH3 flow rate in the initial part of HT-GaN growth has an effect on both full-width at half-maximum (FWHM) values obtained from HRXRD results and intensities of yellow luminescence peaks. It is seen that the FWHM values obtained from the symmetric (00.2) omega scan increased as the NH3 flow rates in the initial part of HT-GaN growth increased. It is demonstrated that the intensities of yellow luminescence peaks are very sensitive to NH3 flow rates in the initial part of HT-GaN growth.

In this study, we implemented reversible current switching (RCS) of 100 mA in a two-terminal device based on a vanadium dioxide (VO2) thin film, which could be controlled by far-infrared (FIR) laser pulses. The VO2 thin films used for fabrication of two-terminal devices were grown on sapphire (Al2O3) substrates using a pulsed laser deposition method. An optimal deposition condition was determined by analyzing the resistance-temperature curves of deposited VO2 thin films and the current–voltage characteristics of two-terminal devices based on these films, which were suggested in our previous works. The film surface of the VO2-based device was directly irradiated using focused CO2 laser pulses, and the insulator-metal transition or metal-insulator transition of the VO2 thin film could be triggered depending on laser irradiation. Consequently, RCS of up to 100 mA could be accomplished. This on-state current is close to the upper limit of the current flowing through our VO2 device. The switching contrast, defined as the ratio between on-state and off-state currents, was evaluated and found to be ˜11,962. The average rising and falling times of the switched current were found to be ˜29.2 and ˜71.7 ms, respectively. In comparison with our previous work, the improved heat dissipation structure and the high-quality thin film could maintain the switching contrast at a similar level, although the on-state current was increased by about two times.

Generation of ultrawideband electromagnetic radiation by a vacuum photodiode with a plane cesium antimonide photocathode is studied. Thin aluminum plates deposited on a sapphire input window serve as the anode of the photodiode. Electron emission from the photocathode is initiated by the second-harmonic radiation (λ = 385 nm) of a titanium–sapphire laser system with a pulse duration of about 200 fs. Variations in the electric component of the electromagnetic radiation due to changes of the voltage across the interelectrode gap from 13 to 140 kV are measured.

In this study we report chip fabrication process that allows the laser lift-off of the sapphire substrate for the transfer of the GaN based thin film flip chip to the carrier wafer. The fabrication process includes 365-nm ultraviolet flip chip LED wafer align bonding with through-AlN-via wafer and sapphire laser lift-off. n-holes with the diameter of 100 µm were etched on the GaN epilayers for accessing n-type GaN. Through-AlN-via size was 110-µm and filled by Cu electroplating method for the electrical connection. Mechanical stabilization to prevent the GaN epilayers cracking and fragmentation during laser lift-off was achieved by utilizing epoxy based SU-8 photoresist support.

At present, corrosive ingredients are widely employed in chemical mechanical polishing (CMP) of sapphire, bringing a potential threat to both people and environment. This results in high cost and long processing time on the treatment of CMP slurry of sapphire. It is a challenge to develop a novel green CMP for sapphire to meet the stringent requirements of high performance products. In this study, a novel green CMP is proposed for sapphire, consisting of silica nanoparticles of 50 nm, triethanolamine (TEA), sodium metasilicate nonahydrate, and deionized water. After green CMP, surface roughness Ra, root mean square (rms), and peak-to-valley (PV) are 0.11, 0.139, and 1.65 nm, respectively. Material removal rate is 3.31 μm/h during green CMP. To the best of our knowledge, surface roughness Ra and rms after green CMP developed are the lowest on a sapphire wafer, compared with those reported previously. The CMP mechanism is elucidated by X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectra. Sapphire formed Al(OH)4− ions in an alkaline environment, which was chelated by TEA, and removed from the surface of sapphire. These findings provide new insights to fabricate high performance devices of sapphire for the use in semiconductor and microelectronic industries.

This article proposed a novel design for the monolithic micro-LED array, directly integrated with a sapphire microreflector. Its resolution was 300 dpi. Theoretically, each micro-LED pixel owns an individual sapphire microreflector which can directly concentrate rays from an emitting source. Therefore, this study proposed that the optical crosstalk between neighboring micro-LED pixels could be suppressed and the contrast of the micro-LED array improved; as this would be especially beneficial for display. The simulation results showed that the increased thickness of the sapphire microreflector could further improve the optical performance of the micro-LED array. For the fabrication process, the key technology was an integrated process involving the inductively coupled plasma (ICP) etching technology for sapphire and micro-LED fabrication, which was used to fulfill the proposed and reference micro-LED arrays. The measurement results showed that the sapphire microreflector could effectively concentrate the emitting rays and increase the contrast of the micro-LED array. In addition, it also indicated that the inclination angle of the microreflector could further improve optical performance. Therefore, this approach was verified to be capable of improving the performance of the micro-LED display.

We report the synthesis and characterization of non-stoichiometric Ga2O3-x thin films deposited on sapphire (0001) substrates by radio-frequency powder sputtering. The chemical and electronic states of the non-stoichiometric Ga2O3-x thin films were investigated. By sputtering in an Ar atmosphere, the as-grown thin films become non-stoichiometric Ga2O2.7, due to the difference in sputtering yield between Ga and O species of the Ga2O3 target. The electronic states of the thin films consist of ~85% Ga3+ and ~15% Ga1+, corresponding to Ga2O3 and Ga2O, respectively. The films have the electrical characteristics of a semiconductor, with electrical conductivity of approximately 5.0 × 10-4 S cm-1 and a carrier concentration of 4.5 × 1014 cm-3 at 300 K.

The nanotribological properties of Zn0.75Mg0.25O grown on R-plane sapphire using metal-organic vapor-phase epitaxy at different substrate temperatures (RT, 600, 700 and 800 °C) were investigated. A slight sliding track was observed at ramped loads of 250 μN, and an obvious bulge edge surrounding the groove was observed at ramped loads of 1 000 μN. Because of the annealing treatment, all the Zn0.75Mg0.25O coatings showed a reconstruction phenomenon of crystallites. The volumes of the bulge edges were as high as 30% in the annealed specimens and were larger than the volumes of the RT-treated specimens when ramped loads of 1 000 μN were applied. Under frictional loading, atomic force microscopy examination of scratch-tested films indicated lower bonding forces on R-plane sapphire than M-plane sapphire.

There is a need for pressure sensor technology that can operate for longer times at very high temperatures. We propose a sapphire pressure sensor designed to operate at high temperature. A Fabry–Perot (FP) sensing cavity created by directly bonding two sapphire wafers through reactive-ion etching functions as a single sapphire structure for pressure measurement at high temperatures. Applying white-light interferometry and diaphragm deflection theory, the fabricated device is experimentally tested by measuring the pressure over a range of 0.1 to 2.1 MPa at 25–1000 °C. The FP sensing cavity length depends on the pressure and the temperature simultaneously. The FP sensing cavity length varies linearly with pressure at 25 °C, and the linearity is preserved with different sensitivity at high temperatures. The structure of the sensor body, enveloping the cavity inside, varies via the coefficient of thermal expansion of sapphire like a single sapphire wafer, and the FP sensing cavity is tightly sealed without any air leakage at high temperature.

High-quality β-Ga2O3 films were grown on (0001) sapphire substrates at various substrate temperature by pulsed laser deposition (PLD) in a high vacuum chamber. Low pressure (1.6 mPa) and high reactivity oxygen plasma was introduced as reaction gas. The films were used to fabricate metal–semiconductor–metal (MSM) solar-blind photodetectors by electron-beam evaporation. The β-Ga2O3 -based photodetector exhibited high performance with a low dark current (about 40 pA), fast response speed (τrise: 0.17 s, τdecay: 0.03 s) and high responsivity (0.35 A/W). These results represent the high quality of β-Ga2O3 films and excellent performance for PLD-grown β-Ga2O3 -based MSM solar-blind photodetectors.

The aim of this paper is to give an experimental evidence that point defects (most probably gallium vacancies) induce decomposition of InGaN quantum wells (QWs) at high temperatures. In the experiment performed, we implanted GaN:Si/sapphire substrates with helium ions in order to introduce a high density of point defects. Then, we grew InGaN QWs on such substrates at temperature of 730 °C, what caused elimination of most (but not all) of the implantation-induced point defects expanding the crystal lattice. The InGaN QWs were almost identical to those grown on unimplanted GaN substrates. In the next step of the experiment, we annealed samples grown on unimplanted and implanted GaN at temperatures of 900 °C, 920 °C and 940 °C for half an hour. The samples were examined using Photoluminescence, X-ray Diffraction and Transmission Electron Microscopy. We found out that the decomposition of InGaN QWs started at lower temperatures for the samples grown on the implanted GaN substrates what provides a strong experimental support that point defects play important role in InGaN decomposition at high temperatures.

A new method for accurate measurement of the microwave surface resistance of flat metal plates is proposed and verified experimentally, based on a sapphire dielectric resonator. System losses are accounted for by having continuous and controlled variation of the distance between the dielectric and the sample under test.

Low dislocation AlN films are the key to prepare high-quality deep ultraviolet emission devices. So, how to reduce the dislocation of the films under the conditions of low cost and high efficiency has become a challenge in the film epitaxy growth. Therefore, this paper combined the magnetron sputtering and high-temperature annealing (HTA) technology, exploring thermal annealing of high-miscut-angle AlN films along different directions. High-resolution X-ray diffraction (XRD) and an optical microscope (OM) were used to characterize the film qualities. After annealing at 1400–1650 °C, the quality of sputtered AlN films improved significantly. The full width at half maximum (FWHM) of (0002) and (10–12) rocking curves decreased as the miscut angles of sapphire increased. The minimum values were obtained when the sapphire substrate had 4° miscut angles along from (0001) to the (11–20) direction. Raman spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) further revealed the mechanism of enhancing the film quality by annealing. The essence of annealing to improve the film quality lies in the elimination of grain boundaries.

Group IVB (Zr and Hf) transition metal dichalcogenides (TMDs) have attracted considerable attention due to their predicted excellent electronic properties that are superior to group VIB TMDs. However, the synthesis of high-quality ZrSe2 layers is seldom reported, greatly hindering the development of this new field. Herein, the epitaxial growth of ZrSe2 on c-plane sapphire substrates is, for the first time, demonstrated using the low-pressure chemical vapor deposition (CVD) method. Impressively, the CVD-grown high-quality ZrSe2 layers exhibit an atomically sharp interface with the underlying substrate, and their epitaxial relationship is determined to be: ZrSe2 (0001)[10–10]||Al2O3 (0001)[11–20]. The electronic band structures of ZrSe2 are calculated using density functional theory methods, showing an indirect band gap of 1.19 eV and a minimum direct band gap of 1.79 eV, respectively. The band gap of ZrSe2 layers is also determined from the UV-visible absorption spectra, which is in good agreement with our band-structure calculations. Furthermore, a photodetector was fabricated based on the CVD-grown ZrSe2 layer on a sapphire substrate, which exhibits a stable and appreciable photoresponse for visible light.