Search

The fabrication of InGaN-based blue 4✕4 array micro-LEDs (μLEDs) with 40 μm ✕40 μm chip size and 2✕2 array μLEDs with 80 μm ✕80 μm chip size etching by the inductive coupled plasma reactive ion etching (ICPRIE) and defect-free neutral beam etching (NBE) processes was studied in this work. In μLEDs of this size, the influence of defects formation in the sidewalls on EQE was evaluated. There was almost no difference in EQE between μLEDs array etched by the NBE process no matter 40 μm ✕40 μm and 80 μm ✕80 μm, but the dependence was observed in the ICPRIE. Even with this size, it was found that the size effect of EQE is smaller than that in case of using ICPRIE for defect-free neutral beam etching. This impact is substantial since μLED predominantly operated at low current density, around 1–5 A/cm2. Consequently, the reduction of defect density, encompassing both internal and sidewall defects, becomes imperative even in 40–80 μm InGaN-based μLEDs. This not only improves the overall efficiency of μLEDs but also fortifies the brightness stability of μLED displays if process etching by NBE. It was also found that the etching shape had an influence on EQE. It could be attributed to fact that the etching profile angle of NBE was more vertical than that of ICPRIE. Because the different angles of the mesa resulted in different light intensity. The μLEDs emitting with a wavelength of 450 nm, the light extraction efficiency and intensity at a mesa angle 58° of NBE etching μLEDs was about 8% lower than those of an angle (38°) of ICPRIE etching μLEDs by simulation.

In this work, we have fabricated a highly sensitive direct irradiating X-ray photodetector (DXPD) based on Zinc Gallium Oxide (ZnGa2O4) epilayers with a metal-semiconductor-metal structure. The ZnGa2O4 epilayers were grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). To test the DXPD's capabilities, we subjected it to a synchrotron hard X-ray source with an energy of 10 keV, and measured incident radiation flux ranging from 5.7✕107 to 4.6 ✕1011 counts/sec. The effect of changing the applied bias voltage on the time response of the DXPD was investigated. The sensitivity of hard XPDs was compared using gallium oxide (β-Ga2O3) epilayer grown by MOCVD. The results showed that ZnGa2O4 DXPD had approximately 104 times greater sensitivity than the β-Ga2O3 based XPD. ZnGa2O4 based detectors also exhibited remarkable sensitivity of 2.87 × 109 μC Gyair−1cm−2 for the incident flux of 5.7✕107 counts/sec at 15 V. Additionally, the sensitivity was examined in terms of applied bias and dose rate. Based on these observations, it can be concluded that ZnGa2O4 epilayers grown by MOCVD hold immense potential for use in high-performance hard XPDs.

The native amorphous silicon oxide (SiO2) layer formed on the Si substrate leads to the (100) preferred orientation for β-phase gallium oxide (β-Ga2O3), which encounters various defects in β-Ga2O3, such as twin boundaries and stacking faults etc. The (111) preferred orientation of titanium nitride (TiN) hetero-buffer layer can be used in the interface between β-Ga2O3 and Si substrates to reduce the lattice mismatch between them and increase the (˗201) preferred orientation for β-Ga2O3. The lattice mismatch between TiN (111) and β-Ga2O3 (˗201) is 0.76%, which is less than the β-Ga2O3 (˗201)/Si (111) about ˗6.3%. The β-Ga2O3 and TiN films were grown using radio-frequency magnetron sputtering on Si substrates, which possess polycrystalline nature as revealed using X-ray diffraction patterns and high-resolution transmission electron micrographs. The optimal parameters are found as, process atmosphere: Ar = 10 sccm, RTA: 800 °C for β-Ga2O3/TiN (300 nm)/Si. This work highlights the effect of the TiN hetero-buffer layer, the process atmosphere, and annealing temperatures on the microstructural and surface morphology of β-Ga2O3 films. The lateral Schottky barrier diode (SBD) were fabricated using the optimized β-Ga2O3/TiN (300 nm)/Si film. The Baliga's Figure of Merit (BFOM) of the lateral SBD is 7.60 × 10−2 kW/cm2, which exhibits 4 order of BFOM higher than that of β-Ga2O3/Si SBD due to interface engineering. The β-Ga2O3/TiN (300 nm)/Si hetero-structure demonstrates a promising material to be employed in the next generation β-Ga2O3 based power devices.

β-Ga2O3 epilayers with a 210 nm thickness were successfully grown on c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Highly resistive unintentionally doped (UID) epilayers are studied, as are Si ion-implantated samples with doses of 1✕1014, 6✕1014 and 1✕1015 cm−2 at 30 keV to improve β-Ga2O3 epilayer conductivity. Schottky barrier diodes (SBDs) were fabricated using optimized growth parameters and electrical measurements performed for both UID and Si-implanted β-Ga2O3 material. The forward current density (J) of an UID SBD at 2 V was 62 nA/cm2 with breakdown voltage (Vbr) of 1.03 kV and leakage J of 10 μA/cm2. The forward J improved by eight orders of magnitude after Si implantation. In this case, Vbr reduced to 680 V combined with a high leakage J of ∼A/cm2 for doses of 1✕1015cm−2. A hard breakdown of 553 V was achieved with a Si-ion dose of 1✕1014 cm−2 with comparatively less leakage than samples with higher dose amounts.

The major factors associated with the manufactured structures and photon emission intensity distribution must be accurately identified for the complicated optical design parameters associated with micro-LED pixels. This study presents the methodologies and reveals the sequential calculating protocol in each layer for pixel-level optical simulations, based on which the boundary condition errors associated with common optical simulations can be corrected. Moreover, the optical effect on each epitaxial layer of the micro-LED design is revealed, and the rationality of the setting of the finite-radius receiver with a pseudo-extended substrate material is also explained with respect to the intrinsic and extrinsic pixel-intensity distribution properties. Finally, the design of experiments DOE L18 orthogonal array table is demonstrated by the Taguchi method to explore the principal factors for the parameter design of the micro-LED layers. The results indicate that the sapphire thickness, the P-GaN layer, the buffer layers, and an additional substrate plate are the four significant factors that primarily influence the luminous power and the corresponding uniformity on the exit pupil of micro-LEDs. Based on the luminous power uniformity, the signal-to-noise ratio in the sapphire thickness is 16.9, and the extended substrate plate is 9.8, which is ∼10 times > the interaction design parameter, such as the etching angle and reflective index of the extended substrate of the micro-LED pixel. These specific design factors can be the major optimization parameters for cost control and performance improvement.

Abstract In this research, five sizes (100 × 100, 75 × 75, 50 × 50, 25 × 25, 10 × 10 µm2) of InGaN red micro-light emitting diode (LED) dies are produced using laser-based direct writing and maskless technology. It is observed that with increasing injection current, the smaller the size of the micro-LED, the more obvious the blue shift of the emission wavelength. When the injection current is increased from 0.1 to 1 mA, the emission wavelength of the 10 × 10 μm2 micro-LED is shifted from 617.15 to 576.87 nm. The obvious blue shift is attributed to the stress release and high current density injection. Moreover, the output power density is very similar for smaller chip micro-LEDs at the same injection current density. This behavior is different from AlGaInP micro-LEDs. The sidewall defect is more easily repaired by passivation, which is similar to the behavior of blue micro-LEDs. The results indicate that the red InGaN epilayer structure provides an opportunity to realize the full color LEDs fabricated by GaN-based LEDs.

An omnidirectional reflector (ODR) consisted of (MgF2)/Ag was employed in AlGaInP-based vertical red light-emitting diodes (LEDs) in order to increase the light extraction hence the wall-plug efficiency. In this structure, the dielectric MgF2 layer with low refractive index acted as current blocking and reflection enhancing layer. The cylindrical AuZn alloy micro-contacts perforated through the MgF2 layer and played roles in current spreading and injection. The area ratio of AuZn micro-contacts was optimized to improve the performance of the LED. The results indicated that increasing the area ratio of micro-contacts led to the improvement of current injection uniformity and reduction of forward voltage especially at higher injection current, but at the expense of light extraction by reducing reflection. After optimized, the best performance of red-light LEDs can be obtained with 3% area ratio of micro-contacts.

In this study, monoclinic gallium oxide (β-Ga2O3) epilayer was successfully grown on c-plane, (0001), sapphire substrate by metalorganic chemical vapor deposition (MOCVD) with interplaying growth temperature, TEGa flow rate, and growth time. X-ray diffraction 2θ scans show only three narrow diffraction peaks referred to β-Ga2O3(2¯ 01), (4¯ 02), and (6¯ 03) in all epilayers, indicating a superior crystalline quality. Current-voltage (I–V) measurement reveals that these β-Ga2O3 films are insulating and exhibit high resistance in a range of 1012–1014 Ω. The crystallization characteristics of the epilayers can be effectively improved with thickness through increasing TEGa flow rate and growth time, which was evidenced by X-ray rocking curves and I–V measurements. However, the surface roughness of β-Ga2O3 film increases with growth time and TEGa flow rate. When the growth temperature increases above 825 °C, the thickness of β-Ga2O3 film decreases clearly. Furthermore, it can be found that the growth rate decreased as the growth time increasing. The growth mechanism based on first-principles calculation was proposed as that 3D growth induced by the lattice mismatch between β-Ga2O3 and sapphire starts at nucleation stage, and follows up a lateral growth promoting a 2D growth after the thick epilayer being grown. In addition, the complex chemical reaction between TEGa and oxygen precursors was unraveled by density function theory calculation.

Abstract In recent years, the process requirements of nano-devices have led to the gradual reduction in the scale of semiconductor devices, and the consequent non-negligible sidewall defects caused by etching. Since plasma-enhanced chemical vapor deposition can no longer provide sufficient step coverage, the characteristics of atomic layer deposition ALD technology are used to solve this problem. ALD utilizes self-limiting interactions between the precursor gas and the substrate surface. When the reactive gas forms a single layer of chemical adsorbed on the substrate surface, no reaction occurs between them and the growth thickness can be controlled. At the Å level, it can provide good step coverage. In this study, recent research on the ALD passivation on micro-light-emitting diodes and vertical cavity surface emitting lasers was reviewed and compared. Several passivation methods were demonstrated to lead to enhanced light efficiency, reduced leakage, and improved reliability.

Abstract The mechanism of carrier recombination in downsized μ-LED chips from 100 × 100 to 10 × 10 μm2 on emission performance was systemically investigated. All photolithography processes for defining the μ-LED pattern were achieved by using a laser direct writing technique. This maskless technology achieved the glass-mask-free process, which not only can improve the exposure accuracy but also save the development time. The multi-functional SiO2 film as a passivation layer successfully reduced the leakage current density of μ-LED chips compared with the μ-LED chips without passivation layer. As decreasing the chip size to 10 × 10 μm2, the smallest chip size exhibited the highest ideality factor, which indicated the main carrier recombination at the high-defect-density zone in μ-LED chip leading to the decreased emission performance. The blue-shift phenomenon in the electroluminescence spectrum with decreasing the μ-LED chip size was due to the carrier screening effect and the band filling effect. The 10 × 10 μm2 μ-LED chip exhibited high EQE values in the high current density region with a less efficiency droop, and the max-EQE value was 18.8%. The luminance of 96 × 48 μ-LED array with the chip size of 20 × 20 μm2 exhibited a high value of 516 nits at the voltage of 3 V.

Aggregation/disaggregation properties in organic/inorganic interfaces have been intensively investigated recently because modulation of the aggregation effect can enhance the fluorescent emission, facilitate light scattering and strengthen the material strength. In this study, bisindolo quinoxaline-tips (BIQ-TIPs) organic polymers dropped on ZnO nanorods (NRs) to form organic/inorganic hybrid photosensing materials. Multiple morphological and material characterizations reveal that as-deposited BIQ-TIPs polymers self-aggregated on ZnO NR surfaces. UV/VIS measurements and photoluminescence (PL) mapping indicate that the absorption spectra of ZnO NRs can be broadened by incorporating BIQ-TIPs on top of ZnO NRs. Furthermore, light photosensitive measurements indicate that BIQ-TIPs /ZnO NRs-based devices exhibited better UV sensing behaviors than ZnO NR-based devices. Interestingly, BIQ-TIPs /ZnO NRs still possessed moderate green light sensing capability while ZnO NRs and BIQ-TIPs only samples possessed no green light sensing capability. Owing to their compact size, facile fabrication, and versatility, BIQ-TIPs /ZnO NR devices show promise for integration with BIQ-TIPs analogue-based electronic devices and future broadband sensing and light-harvesting applications.

The enhanced light output efficiency of passive-matrix micro light-emitting-diode (LED) display was achieved by employing the tapered sidewalls and distributed-Bragg-reflector (DBR) passivation structure. The oblique angles at the bottom of multi-quantum wall and n-GaN are 48.9° and 21.8°, which can favor the planarization structure of pixel interconnection. As increasing the number of DBR (SiO2/TiO2) stacking from 3.5 to 5.5 pairs, the reflectance increased obviously from 81.4% to 98.0% at the wavelength of 450 nm. As the micro-LED display with a multi-function DBR structure, the output power of 1.07 mW under 1 mA, the external-quantum efficiency of 42% under 0.2 mA, and the luminance of 435 nits were obtained.

A 0.28-inch InGaN-based blue micro-LED display with 256 pixel-per-inch resolution and a pitch of 100 μm was successfully fabricated in this study. A thick Ti/Al/Ti/Au interconnection metal was deposited on the n-type gallium nitride (n-GaN) region to reduce the interconnection resistance. The micro-LED array with interconnection metal exhibits better electrical property consistency as compared with that of the traditional one. The output power, forward voltage, and external quantum efficiency of micro-LED, which measured under 1-mA current injection with the full lighting mode, are 0.8 mW, 3.0 V, and 10%, respectively. This technique has the potential to integrate InGaN-based LEDs with quantum dots for full-color applications.

Zn and Al-incorporated ZnGa2O4 films (ZGO:Zn and ZGO:Al) were deposited on sapphire substrates using radio-frequency magnetron sputtering in this work. The effects of Zn and Al incorporation on the microstructural and optoelectronic properties of ZGO films were systematically investigated and compared with each other. This investigation revealed that incorporation of Al enhanced the characteristics of the ZGO film, whereas incorporation of Zn affected the characteristics of the ZGO film. The annealed ZGO:Al film revealed high crystallinity, average transmittance of >82%, and wide-bandgap of 5.18 eV. First principles calculations were performed to investigate the defects associated with the ZGO:Al structure. The Al incorporated ZGO PD exhibited an optimum metal–semiconductor–metal photodetector achievement with a photo/dark current ratio of ∼104 order and responsivity of 3.01 A/W (at 3 V and 220 nm), demonstrating the responsivity of ZGO PD (0.25 A/W) can be increased up to 12 times by incorporating Al in ZGO films. This enhancement in the characteristics of the ZGO:Al film can be ascribed to the high crystalline nature and the formation of significant amount of oxygen vacancies in this film. These results demonstrate the potential of Al incorporated ZGO films in wide-bandgap devices and deep-ultraviolet applications.

This paper emphasizes that the furnace pressure, crucible rotation, and pulling rate have important effects on interstitial oxygen (Oi) concentrations and micro-defects during growth in a Czochralski single-crystal silicon (CZ-Si) growth furnace. Since oxygen in a silicon ingot influences minority carrier lifetime, different set-points of furnace pressure and crucible rotation were controlled to achieve different degrees of Oi. The Oi content has a positive correlation with furnace pressure and crucible rotation. Various numbers of micro-defects were generated under the influence of different pulling rates, owing to the transformation from liquid to solid. The sample also underwent Secco etching and a high-temperature wet oxidation to observe defects caused by the Oi concentration and pulling rate, namely, flow pattern defects (FPDs) and oxidation-induced stacking faults (OISFs). Optical microscopy was employed to confirm the surface topography, and for defect number counting, to observe the correlation between the defects and the minority carrier lifetime. The overall results show that the minority carrier lifetime is mainly dominated by OISFs under high Oi content and FPDs under low Oi content. Therefore, growth using a CZ-Si growth furnace should be carried out with low furnace pressure, low crucible rotation, and low pulling rate to reduce micro-defects.

In recent years, the application of (In, Al, Ga)N materials in photovoltaic devices has attracted much attention. Like InGaN, it is a direct band gap material with high absorption at the band edge, suitable for high efficiency photovoltaic devices. Nonetheless, it is important to deposit high-quality GaN material as a foundation. Plasma-enhanced atomic layer deposition (PEALD) combines the advantages of the ALD process with the use of plasma and is often used to deposit thin films with different needs. However, residual oxygen during growth has always been an unavoidable issue affecting the quality of the resulting film, especially in growing gallium nitride (GaN) films. In this study, the NH3-containing plasma was used to capture the oxygen absorbed on the growing surface to improve the quality of GaN films. By diagnosing the plasma, NH2, NH, and H radicals controlled by the plasma power has a strong influence not only on the oxygen content in growing GaN films but also on the growth rate, crystallinity, and surface roughness. The NH and NH2 radicals contribute to the growth of GaN films while the H radicals selectively dissociate Ga-OH bonds on the film surface and etch the grown films. At high plasma power, the GaN film with the lowest Ga-O bond ratio has a saturated growth rate, a better crystallinity, a rougher surface, and a lower bandgap. In addition, the deposition mechanism of GaN thin films prepared with a trimethylgallium metal source and NH3/Ar plasma PEALD involving oxygen participation or not is also discussed in the study.

Hafnium oxide (HfO2) thin film has remarkable physical and chemical properties, which makes it useful for a variety of applications. In this work, HfO2 films were prepared on silicon through plasma enhanced atomic layer deposition (PEALD) at various substrate temperatures. The growth per cycle, structural, morphology and crystalline properties of HfO2 films were measured by spectroscopic ellipsometer, grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), field-emission scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. The substrate temperature dependent electrical properties of PEALD–HfO2 films were obtained by capacitance–voltage and current–voltage measurements. GIXRD patterns and XRR investigations show that increasing the substrate temperature improved the crystallinity and density of HfO2 films. The crystallinity of HfO2 films has a major effect on electrical properties of the films. HfO2 thin film deposited at 300 °C possesses the highest dielectric constant and breakdown electric field.

Gallium oxide (Ga2O3) materials can be fabricated via various methods or processes. It is often mentioned that it possesses different polymorphs (α-, β-, γ-, δ- and ε-Ga2O3) and excellent physical and chemical properties. The basic properties, crystalline structure, band gap, density of states, and other properties of Ga2O3 will be discussed in this article. This article extensively discusses synthesis of pure Ga2O3, co-doped Ga2O3 and Ga2O3-metal oxide composite and Ga2O3/metal oxide heterostructure nanomaterials via solution-based methods mainly sol-gel, hydrothermal, chemical bath methods, solvothermal, forced hydrolysis, reflux condensation, and electrochemical deposition methods. The influence of the type of precursor solution and the synthesis conditions on the morphology, size, and properties of final products is thoroughly described. Furthermore, the applications of Ga2O3 will be introduced and discussed from these solution processes, such as deep ultraviolet photodetector, gas sensors, pH sensors, photocatalytic and photodegradation, and other applications. In addition, research progress and future outlook are identified.

The metal-semiconductor-metal photodetectors based on the sputtered gallium oxide films on sapphire substrates after various post-thermal treatments have been investigated. The photodetector performance of the furnace-annealed gallium oxide sample degraded with the increase of annealing temperature from 700 to 1000 °C, resulting from the adverse effect of the aluminum cross-diffusion and polycrystalline formation. By rapid thermal annealing at 800 °C, the gallium oxide film can achieve an optimum photodetector performance with the photo/dark current ratio of 1.78 × 105 (@5V and 230 nm), responsivity of 0.553 A/W, and fast transient response (rise/fall time: 0.2 s/0.1 s). The result is comprehensively better than the previous reports by sputtering, which demonstrates that the quasi-single-crystalline gallium oxide film via rapid thermal process has high potential for deep-ultraviolet photodetector applications.

The promising functional tin oxide (SnOx) has attracted tremendous attention due to its transparent and conductive properties. The stoichiometric composition of SnOx can be described as common n-type SnO2 and p-type Sn3O4. In this study, the functional SnOx films were prepared successfully by plasma-enhanced atomic layer deposition (PEALD) at different substrate temperatures from 100 to 400 °C. The experimental results involving optical, structural, chemical, and electrical properties and morphologies are discussed. The SnO2 and oxygen-deficient Sn3O4 phases coexisting in PEALD SnOx films were found. The PEALD SnOx films are composed of intrinsic oxygen vacancies with O-Sn4+ bonds and then transformed into a crystalline SnO2 phase with increased substrate temperature, revealing a direct 3.5–4.0 eV band gap and 1.9–2.1 refractive index. Lower (300 °C) substrate temperatures can cause precursor condensation and desorption, respectively, resulting in reduced film qualities. The proper composition ratio of O to Sn in PEALD SnOx films near an estimated 1.74 suggests the highest mobility of 12.89 cm2 V−1 s−1 at 300 °C.

Indium tin oxide (ITO) thin films were prepared by high power impulse magnetron sputtering (HiPIMS) and annealed in hydrogen-containing forming gas to reduce the film resistivity. The film resistivity reduces by nearly an order of magnitude from 5.6 × 10−3 Ω·cm for the as-deposited film to the lowest value of 6.7 × 10−4 Ω·cm after annealed at 700 °C for 40 min. The role of hydrogen (H) in changing the film properties was explored and discussed in a large temperature range (300–800 °C). When annealed at a low temperature of 300–500 °C, the incorporated H atoms occupied the oxygen sites (Ho), acting as shallow donors that contribute to the increase of carrier concentration, leading to the decrease of film resistivity. When annealed at an intermediate temperature of 500–700 °C, the Ho defects are thermally unstable and decay upon annealing, leading to the reduction of carrier concentration. However, the film resistivity keeps decreasing due to the increase in carrier mobility. Meanwhile, some locally distributed metallic clusters formed due to the reduction effect of H2. When annealed at a high temperature of 700–800 °C, the metal oxide film is severely reduced and transforms to gaseous metal hydride, leading to the dramatic reduction of film thickness and carrier mobility at 750 °C and vanish of the film at 800 °C.

Amorphous Gallium oxide (Ga2O3) thin films were grown by plasma-enhanced atomic layer deposition using O2 plasma as reactant and trimethylgallium as a gallium source. The growth rate of the Ga2O3 films was about 0.6 Å/cycle and was acquired at a temperature ranging from 80 to 250 °C. The investigation of transmittance and the adsorption edge of Ga2O3 films prepared on sapphire substrates showed that the band gap energy gradually decreases from 5.04 to 4.76 eV with the increasing temperature. X-ray photoelectron spectroscopy (XPS) analysis indicated that all the Ga2O3 thin films showed a good stoichiometric ratio, and the atomic ratio of Ga/O was close to 0.7. According to XPS analysis, the proportion of Ga3+ and lattice oxygen increases with the increase in temperature resulting in denser films. By analyzing the film density from X-ray reflectivity and by a refractive index curve, it was found that the higher temperature, the denser the film. Atomic force microscopic analysis showed that the surface roughness values increased from 0.091 to 0.187 nm with the increasing substrate temperature. X-ray diffraction and transmission electron microscopy investigation showed that Ga2O3 films grown at temperatures from 80 to 200 °C were amorphous, and the Ga2O3 film grown at 250 °C was slightly crystalline with some nanocrystalline structures.

CdSe/CdS with ZnS/ZnO shell quantum dots (QDs) are synthesized by a one-pot method with various oleylamine (OLA) contents. The crystal structures of the QDs were analyzed by X-ray diffractometry, which showed ZnS diffraction peaks. It was represented that the ZnS shell was formed on the surface of the CdSe/CdS core. Interestingly, QDs with a high OLA concentration exhibit diffraction peaks of ZnS/ZnO. As a result, the thermal stability of QDs with ZnS/ZnO shells exhibits better performance than those with ZnS shells. In addition, the photoluminescence intensity of QDs with ZnS/ZnO shells shows a relatively slow decay of 7.1% compared with ZnS shells at 85 °C/85% relative humidity aging test for 500 h. These indicate that QDs with different OLA modifications can form ZnS/ZnO shells and have good stability in a harsh environment. The emission wavelength of QDs can be tuned from 505 to 610 nm, suitable for micro-LED display applications.

A red-light micro LED display made of an AlGaInP epilayer with a resolution of 64 × 32 pixels, a pitch of 175 μm and a luminous area of 1 cm × 0.5 cm was fabricated and characterized in this study. The AlGaInP epilayer was bonded to double polished sapphire substrate by wafer-bonding technique and then removing the absorbing GaAs substrate. In this design, the ITO was applied as one of the conducting electrodes of the emitting surface, which can be beneficial since the emitting light is not shielded by metal electrodes. The other key process for LED panel fabrication is planarization. Polymer material was used to fill the gap between each pixel, which was used to prevent a short or open circuit using the planarization process. The driving mode of this display is passive multi-electrode addressable controlling. The luminance of this micro-LED panel is more than 450 nits with an operating voltage of 3 V which is three times higher than that of the OLED operating in the same driving mode.

ZnO/ZnS nanocomposite-based nanostructures exhibit dual light and gas sensing capabilities. To further boost the light/dual sensing properties, gold nanoparticles (Au NPs) were incorporated into the core-shell structures. Multiple material characterizations revealed that Au NPs were successfully well spread and decorated on ZnO/ZnS nanostructures. Furthermore, our findings show that the addition of Au NPs could enhance both 365 nm UV light sensing and hydrogen gas sensing in terms of light/gas sensitivity and light/gas response time. We postulate that the optimization of gas/light dual sensing capability may result from the induced electric field and inhabitation of electron-hole recombination. Owing to their compact size, simple fabrication, and stable response, ZnO/ZnS/Au NPs-based light/gas dual sensors are promising for future extreme environmental monitoring.

Spinel ZnGa2O4 films were grown on c-plane sapphire substrates at the substrate temperature of 400 °C by radio-frequency magnetron sputtering. Post thermal annealing was employed at the annealing temperature of 700 °C in order to enhance their crystal quality. The effect of thermal annealing on the microstructural and optoelectronic properties of ZnGa2O4 films was systematically investigated in various ambiences, such as air, nitrogen, and oxygen. The X-ray diffraction patterns of annealed ZnGa2O4 films showed the crystalline structure to have (111) crystallographic planes. Transmission electron micrographs verified that ZnGa2O4 film annealed under air ambience possesses a quasi-single-crystalline structure. This ZnGa2O4 film annealed under air ambience exhibited a smooth surface, an excellent average transmittance above 82% in the visible region, and a wide bandgap of 5.05 eV. The oxygen vacancies under different annealing ambiences were revealed a substantial impact on the material and photodetector characteristics by X-ray photoelectron spectrum investigations. ZnGa2O4 film exhibits optimal performance as a metal-semiconductor-metal photodetector when annealed under air ambience. Under these conditions, ZnGa2O4 film exhibits a higher photo/dark current ratio of ~104 order, as well as a high responsivity of 2.53 A/W at the bias of 5 V under an incident optical light of 240 nm. These results demonstrate that quasi-single-crystalline ZnGa2O4 films have significant potential in deep-ultraviolet applications.

Abstract A novel fabrication method for single crystalline ZnO nanorods by pulsed laser deposition (PLD) using a chemical-bath-deposited ZnS seed layer is proposed. For the substrate temperature (Ts) lower than 700 °C, the PLD-ZnO showed a polycrystalline phase and film-type morphology, resulting from the ZnS seed layer with a cubic phase. However, the ZnS film became a sacrifical layer and single crystalline ZnO(002) nanorods can be achieved at Ts of 900 °C, where ZnS was decomposed to zinc metals and sulfur fumes. The transformation from ZnO film to nanorod microstructure was demonstrated with the change of ZnS layer into Zn grains. Enhanced performance of the metal-semiconductor-metal photodetectors were fabricated with ZnO/ZnS samples grown at Ts of 500, 700, and 900 °C. The responsivities (@1 V and 370 nm) of these three devices were 1.71, 6.35, and 98.67 A/W, while their UV-to-visible discrimination ratios were 7.2, 16.5, and 439.1, respectively. Obviously, a higher light-capturing efficiency was obtained in the 900 °C-grown ZnO/ZnS device owing to its one-dimensional nanostructure with high crystal quality. The results indicate PLD combined with a sacrifical nanostructure is a promising method for obtaining high-quality ZnO nanorods, which paves the way for the fabrication of high performance ZnO-based devices.

High-voltage light-emitting diodes (HV-LEDs) were prepared with 4 × 2 microcells. A novel technique for enhancing the light extraction of HV-LEDs by using wet-etched chamfer structures in the sidewalls of each cell is proposed. The thicknesses of the u-GaN layers used were in the range of 3-7 μm. Simulations revealed that the light extraction of the HV-LEDs with chamfer structures would be enhanced by increasing the u-GaN thickness. The output power (@80 mA) of the HV-LEDs without chamfer structures was 538.0-539.1 mW. However, the output powers (@80 mA) of the HV-LEDs with chamfer structures and u-GaN thicknesses of 3, 5, and 7 μm were increased to 555.3, 573.1, and 561.6 mW, respectively. The 7 μm thick u-GaN layer led to an extremely large thickness of the HV-LED epitaxial structure, which caused difficulties during the wet etching process. Because of the apparent decrease in the wet etching rate of GaN, the damages to the epitaxial structures of the HV-LED with the 7 μm thick u-GaN was more obvious. Therefore, the device's light extraction was slightly reduced. The results confirm that chamfer structures are highly useful for improving the performance of HV-LEDs, especially for the u-GaN thickness of 5 μm.

Spinel ZnGa2O4 has received significant attention from researchers due to its wide bandgap and high chemical and thermal stability; hence, paving the way for it to have potential in various applications. This review focuses on its physical, optical, mechanical and electrical properties, contributing to the better understanding of this material. The recent trends for growth techniques and processing in the research and development of ZnGa2O4 from bulk crystal growth to thin films are discussed in detail for device performance. This material has excellent properties and is investigated widely in deep-ultraviolet photodetectors, gas sensors and phosphors. In this article, effects of substrate temperature, annealing temperature, oxygen partial pressure and zinc/gallium ratio are discussed for device processing and fabrication. In addition, research progress and future outlooks are also identified.

Protective oxide coatings, such as Al2O3 and Y2O3 coatings, are widely used in semiconductor industries because of their hardness, high wear resistance, dielectric strength, high corrosion resistance, and chemical stability for plasma chambers [...]