Search Results (55)

Laser annealing of oxide functional thin films makes them compatible with substrates of various types, especially flexible materials. The effects of optical annealing on Ni-doped ZnO thin films were the subject of investigation and analysis in this study. Using pulsed laser deposition, we deposited polycrystalline ZnNiO films on sapphire and silicon substrates. The deposited film was annealed by laser heating. A continuous CO₂ laser was used for this purpose. The uniformly distributed long-wavelength radiation of the CO₂ laser can penetrate deeper from the surface of the thin film compared to short-wavelength lasers such as UV and IR lasers. After growth, optical post-annealing processes were applied to improve the conductive properties of the films. The crystallinity and surface morphology of the grown films and annealed films were analyzed using SEM, and their electrical parameters were evaluated using van der Pauw effect measurements. We used electrical conductivity measurements and investigated the photovoltaic properties of the ZnNiO film. After CO₂ laser annealing, changes in both the crystalline structure and surface appearance of ZnO were evident. Subsequent to laser annealing, the crystallinity of ZnO showed both change and degradation. High-power CO₂ laser annealing changed the structure to a mixed grain size. Surface nanostructuring occurred. This was confirmed by SEM morphological studies. After irradiation, the electrical conductivity of the films increased from 0.06 Sm/cm to 0.31 Sm/cm. The lifetime of non-equilibrium charge carriers decreased from 2.0·10⁻⁹ s to 1.2·10⁻⁹ s. Full article

A novel empirical method for fabricating Van der Pauw Hall test samples on GaN epitaxy is proposed and tested, which enables rapid preparation of Van der Pauw Hall test samples on both conductive and non-conductive substrates. Compared to traditional Van der Pauw Hall sample preparation, this approach eliminates the need for annealing to form Ohmic contacts, thereby facilitating more accurate measurement of the resistivity, Hall coefficient, majority carrier concentration, and mobility in semiconductor wafers, which may be subject to change after high-temperature annealing. This method is based on the use of specialized plasma dry-etched patterns to form the Ohmic electrodes, which reduces the metal–semiconductor contact barrier, allowing the tunneling current to dominate and thus forming Ohmic contacts. In the validation experiments, three different substrate materials for GaN-epi—silicon, sapphire, and silicon carbide—were selected for the preparation of the Van der Pauw Hall test samples, followed by testing and analysis to confirm the accuracy of the new test method. The measurement results for the electron mobility and carrier concentration on the sapphire and silicon carbide substrate samples were verified via the contactless RF reflectance mapping method, with an average difference only 4.0% and 7.0%, respectively, and a minimum of only 0.53% and 1.8%. The proposed fabrication method features a relatively simple structure, enabling rapid preparation and avoiding the damage and errors caused by high-temperature annealing processes. It shows great potential for industrial application on precise carrier property measurements, especially for GaN-epi on a conductive substrate. Full article

Monolithic micro LED display arrays show potential for application in small-area display modules, such as augmented reality (AR) displays. Due to the short distance between micro LEDs and the monolithic transparent substrate, a light crosstalk phenomenon exists between adjacent micro LED pixels, decreasing the array’s display definition. In this paper, a 64 × 64 GaN micro LED monolithic display array was fabricated on a silicon-based drive circuit. The micro LED size was 20 μm × 20 μm, and the pitch between micro LEDs was 28 μm. To suppress the optical crosstalk between adjacent micro LEDs in the array, we etched a photonic crystal structure using a focused ion beam (FIB) on the micro LED sapphire substrate. Measurements of the micro LED nearfield electroluminescence (EL) and finite element method (FEM) calculations demonstrated that the light expansion was confined in the photonic crystal micro LED with a thinner substrate. The presented work provides references regarding the fabrication of monolithic micro LED arrays and the control of crosstalk in displays. Full article

Diffractive optical elements (DOEs) are specialized optical components that manipulate light through diffraction for various applications, including holography, spectroscopy, augmented reality (AR) and virtual reality (VR), and light detection and ranging (LiDAR). The performance of DOEs is highly determined by fabricated materials and fabrication methods, in addition to the numerical simulation design. This paper presents a microfabrication technique optimized for DOEs, enabling precise control of critical parameters, such as refractive index (RI) and thickness. Using photolithography, we fabricated high-precision photoresist patterns on silicon and sapphire substrates, with 3 × 3 and 3 × 5 DOE beam splitter as examples. The results show a strong match between simulation and experimental data, with discrepancies of just 0.53% and 0.57% for DOE on silicon and sapphire substrates, respectively. This approach offers potential for advancing high-performance DOE devices in semiconductor manufacturing, supporting next-generation optical systems. Full article

In this study, we utilized a terahertz chemical microscope (TCM) to map surface potential changes induced by molecular interactions on silicon-on-sapphire (SOS) substrates. By functionalizing the SOS substrate with DNA aptamers and an ion-selective membrane, we successfully detected and visualized aptamer–neurochemical complexes through the terahertz amplitude. Additionally, comparative studies of DNA aptamers in PBS buffer and artificial cerebrospinal fluid (aCSF) were performed by computational structure modeling and terahertz measurements. Beyond neurochemicals, we also investigated calcium ions, measuring their concentrations in PDMS-fabricated micro-wells using minimal sample volumes. Our results highlight the capability of TCM as a powerful, label-free, and sensitive platform for the probing and mapping of surface potential arising from molecular interactions, with broad implications for biomedical diagnostics and research. Full article

Sapphire has various applications in photonics due to its broadband transparency, high-contrast index, and chemical and physical stability. Photonics integration on the sapphire platform has been proposed, along with potentially high-performance lasers made of group III–V materials. In parallel with developing active devices for photonics integration applications, in this work, silicon nitride optical waveguides on a sapphire substrate were analyzed using the commercial software Comsol Multiphysics in a spectral window of 800~2400 nm, covering the operating wavelengths of III–V lasers, which could be monolithically or hybridly integrated on the same substrate. A high confinement factor of ~90% near the single-mode limit was obtained, and a low bending loss of ~0.01 dB was effectively achieved with the bending radius reaching 90 μm, 70 μm, and 40 μm for wavelengths of 2000 nm, 1550 nm, and 850 nm, respectively. Furthermore, the use of a pedestal structure or a SiO₂ bottom cladding layer has shown potential to further reduce bending losses. The introduction of a SiO₂ bottom cladding layer effectively eliminates the influence of the substrate’s larger refractive index, resulting in further improvement in waveguide performance. The platform enables tightly built waveguides and small bending radii with high field confinement and low propagation losses, showcasing silicon nitride waveguides on sapphire as promising passive components for the development of high-performance and cost-effective PICs. Full article

The application of GaN HEMTs on silicon substrates in high-voltage environments is significantly limited due to their complex buffer layer structure and the difficulty in controlling wafer warpage. In this work, we successfully fabricated GaN power HEMTs on 6-inch sapphire substrates using a CMOS-compatible process. A 1.5 µm thin GaN buffer layer with excellent uniformity and a 20 nm in situ SiN gate dielectric ensured uniformly distributed V_TH and R_ON across the entire 6-inch wafer. The fabricated devices with an L_GD of 30 µm and W_G of 36 mm exhibited an R_ON of 18.06 Ω·mm and an off-state breakdown voltage of over 3 kV. The electrical mapping visualizes the high uniformity of R_ON and V_TH distributed across the whole 6-inch wafer, which is of great significance in promoting the applications of GaN power HEMTs for medium-voltage power electronics in the future. Full article

Fabry–Perot interferometers (FPIs), comprising foundry-compatible dielectric thin films on sapphire wafer substrates, were investigated for possible use in chemical sensing. Specifically, structures comprising two vertically stacked distributed Bragg reflectors (DBRs), with the lower DBR between a sapphire substrate and a silicon-oxide (SiO₂) resonator layer and the other DBR on top of this resonator layer, were investigated for operation in the near-ultraviolet (near-UV) range. The DBRs are composed of a stack of nitride-rich silicon-nitride (SiN_x) layers for the higher index and SiO₂ layers for the lower index. An exemplary application would be formaldehyde detection at sub-ppm concentrations in air, using UV absorption spectroscopy in the 300–360 nm band, while providing spectral selectivity against the main interfering gases, notably NO₂ and O₃. Although SiN_x thin films are conventionally used only for visible and near-infrared optical wavelengths (above 450 nm) because of high absorbance at lower wavelengths, this work shows that nitride-rich SiN_x is suitable for near-UV wavelengths. The interplay between spectral absorbance, transmittance and reflectance in a FPI is presented in a comparative study between one FPI design using stoichiometric material (Si₃N₄) and two designs based on N-rich compositions, SiN_1.39 and SiN_1.49. Spectral measurements confirm that if the design accounts for phase penetration depth, sufficient performance can be achieved with the SiN_1.49-based FPI design for gas absorption spectroscopy in near-UV, with peak transmission at 330 nm of 64%, a free spectral range (FSR) of 20 nm and a full-width half-magnitude spectral resolution (FWHM) of 2 nm. Full article

Hydrogen energy is the clean energy with the most potential in the 21st century. The microchannel reactor for methanol steam reforming (MSR) is one of the effective ways to obtain hydrogen. Ceramic materials have the advantages of high temperature resistance, corrosion resistance, and high mechanical strength, and are ideal materials for preparing the catalyst support in microchannel reactors. However, the structure of ceramic materials is hard and brittle, and the feature size of microchannel is generally not more than 1 mm, which is difficult to process using traditional processing methods. Diamond wire saw processing technology is mainly used in the slicing of hard and brittle materials such as sapphire and silicon. In this paper, a microchannel with a periodic corrugated microstructure was fabricated on a ceramic plate using diamond wire sawing, and then as a catalyst support when used in a microreactor for MSR hydrogen production. The effects of wire speed and feed speed on the amplitude and period size of the periodic corrugated microstructure were studied using a single-factor experiment. The microchannel surface morphology was observed via SEM and a 3D confocal laser microscope under different processing parameters. The microchannel samples obtained under different processing parameters were supported by a multiple impregnation method. The loading strength of the catalyst was tested via a strong wind purge experiment. The experimental results show that the periodic corrugated microstructure can significantly enhance the load strength of the catalyst. The microchannel catalyst support with the periodic corrugated microstructure was put into the microreactor for a hydrogen production experiment, and a good hydrogen production effect was obtained. The experimental results have a positive guiding effect on promoting ceramic materials as the microchannel catalyst support for the development of hydrogen energy. Full article

Low-temperature growth of diamond films using the chemical vapor deposition (CVD) method is not so widely reported and its initial periods of nucleation and growth phenomenon are of particular interest to the researchers. Four sets of substrates were selected for growing diamond films using linear antenna microwave plasma-enhanced CVD (LA-MPCVD). Among them, silicon and sapphire substrates were pre-treated with detonation nanodiamond (DND) seeds before diamond growth, for enhancement of its nucleation. Carbon nanotube (CNT) films on Si substrates were also used as another template for LA-MPCVD diamond growth. To enhance diamond nucleation during CVD growth, some of the CNT films were again pre-treated by the electrophoretic deposition (EPD) of diamond nanoparticles. All these substrates were then put inside the LA-MPCVD chamber to grow diamond films under variable processing conditions. Microwave input powers (1100–2800 W), input power modes (pulse or continuous), antenna-to-stage distances (5–6.5 cm), process gas recipes (with or without CO₂), methane gas percentages (3%–5%), and deposition times (11–120 min) were altered to investigate their effect on the growth of diamond film on the pre-treated substrates. The substrate temperatures were found to vary from as low as 170 °C to a maximum of 307 °C during the alteration of the different processing parameters. Contrary to the conventional MPCVD, it was observed that during the first hour of LA-MPCVD diamond growth, DND seeds and the nucleating structures do not coalesce together to make a continuous film. Deposition time was the most critical factor in fully covering the substrate surfaces with diamond film, since the substrate temperature could not become stable during the first hour of LA-MPCVD. CNTs were found to be oxidized rapidly under LA-MPCVD plasma conditions; therefore, a CO₂-free process gas recipe was used to reduce CNT burning. Moreover, EPD-coated CNTs were found to be less oxidized by the LACVD plasma during diamond growth. Full article

Advancements in astronomical telescopes and cutting-edge technologies, including deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography, have escalated demands and imposed stringent surface quality requirements on optical system components. Achieving near-ideal optical components requires ultra-smooth surfaces with sub-nanometer roughness, no sub-surface damage, minimal surface defects, low residual stresses, and intact lattice integrity. This necessity has driven the rapid development and diversification of ultra-smooth surface fabrication technologies. This paper summarizes recent advances in ultra-smooth surface processing technologies, categorized by their material removal mechanisms. A subsequent comparative analysis evaluates the roughness and polishing characteristics of ultra-smooth surfaces processed on various materials, including fused silica, monocrystalline silicon, silicon carbide, and sapphire. To maximize each process’s advantages and achieve higher-quality surfaces, the paper discusses tailored processing methods and iterations for different materials. Finally, the paper anticipates future development trends in response to current challenges in ultra-smooth surface processing technology, providing a systematic reference for the study of the production of large-sized freeform surfaces. Full article

Hafnium oxide films were deposited on sapphire and silicon (100) substrates using the DC reactive magnetron sputtering technique from a pure hafnium target at different discharge power levels. The influence of the cathode power on the chemical composition, morphology, crystallographic structure and optical properties of the films was investigated. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and Fourier-transform infrared spectroscopy (FTIR) were employed to determine the chemical composition and bonding structure. In all cases, the films were found to be amorphous or nanocrystalline with increased crystalline content as the sputtering power was increased, according to XRD and FTIR. In addition, EDX showed that the films were oxygen-rich. The effect of power deposition on the surface topography and morphology of the films was studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images revealed the emergence of mound morphologies as the cathode power was increased. These features are related to blistering effects probably due to the presence of stress and its promotion within the film thickness. Finally, the optical properties showed an average transmission of 80% in the visible range, and the refractive index determined by spectral ellipsometry (SE) was found to be in the range of 1.85–1.92, close to the reported bulk value. SE was also used to study the film porosity observed by SEM, which can be related to the oxygen-rich character of the films. Full article

Gallium nitride continues to be a material of intense interest for the ongoing advancement of electronic and optoelectronic devices. While the bulk of today’s markets for low-performance devices is still met with silicon and blue/UV LEDs derived from metal–organic chemical vapor deposition gallium nitride grown on foreign substrates such as sapphire and silicon carbide, the best performance values consistently come from devices built on bulk-grown gallium nitride from native seeds. The most prominent and promising of the bulk growth methods is the ammonothermal method of high-pressure solution growth. The state-of-the-art from the last five years in ammonothermal gallium nitride technology is herein reviewed within the general categories of growth technology, characterization and defects as well as device performance. Full article

Lead-based ternary-chalcogenide thin films of the (PbTe)_1−x(PbS)_x system were obtained using the plasma-enhanced chemical-vapor-deposition (PECVD) technique under conditions of a nonequilibrium low-temperature argon plasma of an RF discharge (40.68 MHz) at a reduced pressure (0.01 Torr). High-purity elements were directly used as starting materials, namely Pb, S and Te. Plasma–chemical synthesis was carried out on the surface of c-sapphire and silicon substrate. The physicochemical properties of the films were studied using various analytical methods. The dependence of the Seebeck coefficient, resistivity and power factor on the structural properties and composition has been studied. The thermoelectric characteristics were found to be dependent on film composition. Upon the selection of optimal sulfur concentration, one can increase the power factor compared to single-phase PbS or PbTe films. Full article

Selective area doping via ion implantation is crucial to the implementation of most modern devices and the provision of reasonable device design latitude for optimization. Herein, we report highly effective silicon ion implant activation in GaN via Symmetrical Multicycle Rapid Thermal Annealing (SMRTA) at peak temperatures of 1450 to 1530 °C, producing a mobility of up to 137 cm²/Vs at 300K with a 57% activation efficiency for a 300 nm thick 1 × 10¹⁹ cm⁻³ box implant profile. Doping activation efficiency and mobility improved alongside peak annealing temperature, while the deleterious degradation of the as-grown material electrical properties was only evident at the highest temperatures. This demonstrates efficient dopant activation while simultaneously maintaining low levels of unintentional doping and thus a high blocking voltage potential of the drift layers for high-voltage, high-power devices. Furthermore, efficient activation with high mobility has been achieved with GaN on sapphire, which is known for having relatively high defect densities but also for offering significant commercial potential due to the availability of cheap, large-area, and robust substrates for devices. Full article