In this research, five sizes (100 × 100, 75 × 75, 50 × 50, 25 × 25, 10 × 10 µm
) 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 μm
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.
Monoclinic gallium oxide thin films were grown on (0001) sapphire at various substrate temperatures ranging from 400 to 1000 degreesC by pulsed laser deposition using a KrF excimer laser. The ...structural, optical and compositional properties of the films were analyzed by using x-ray diffraction, transmission electron microscopy, optical transmittance, and Rutherford backscattering spectroscopy. As the substrate temperature was increased to 800 degreesC, the gallium oxide film possesses single crystalline phase with a preferred growth orientation of (-201) plane and higher crystal quality than those at the other temperatures. Optical transmittance measurements reveal the films grown at 600-1000 degreesC exhibit a clear absorption edge at the deep ultraviolet region around 250 nm wavelength. Based on the results of Rutherford backscattering spectroscopy, the O/Ga ratio of gallium oxide film increased gradually with increasing substrate temperature. When the substrate temperature was raised to 800-1000 degreesC, the film composition was close to the formation of Ga sub(2)O sub(3), indicating the O vacancies and defects were reduced. Furthermore, the films grown at 600 and 800 degreesC were chosen to fabricate solar-blind metal-semiconductor-metal photodetectors. At an applied bias of 5 V, the photodetector prepared with 800 degreesC-grown film has a lower dark current of 1.2 x 10 super(-11) A and a higher responsivity of 0.903 A/W (at a wavelength of 250 nm) than those with 600 degreesC-grown films. The better device performance is ascribed to the higher crystal quality and fewer O vacancies in the 800 degreesC-grown film. Moreover, the results indicate the gallium oxide films presented in this study have high potential for deep ultraviolet photodetector applications.
Gallium oxide (Ga2O3) films had been fabricated on Al2O3(0001) substrate by employing pulsed laser deposition (PLD) and annealed at different temperatures under forming gas (FG) atmosphere (95% N2 + ...5% H2). The influence of annealing temperature on the structural, optical, chemical composition, and surface morphological properties of the Ga2O3 thin films was investigated comprehensively. The annealing processes with hydrogen gas play a crucial role in the characteristics of Ga2O3 thin films. A crystallization mechanism of Ga2O3 films controlled by annealing temperature has been proposed firstly and analyzed systematically, which contains three kinds of competitive mechanism, namely the thermal enhanced crystallization, the enhanced H2 dissociative adsorption on Ga2O3 surfaces, and the high‐temperature decomposition of Ga2O3. Both Ga+ and Ga3+ oxidation valence states were presented in all samples, which indicated lattice oxygen deficiency in Ga2O3 films. The variation of the non‐lattice oxygen proportion of Ga2O3 films related to the crystallization mechanism firstly increased and then decreased with the increase of annealing temperature. The detailed crystallization mechanism of PLD‐Ga2O3 films annealed in FG offers a guideline and references for the further fabrication of high‐quality Ga2O3 films and their applications in high‐performance devices.
To acquire device-quality TiOx films usually needs high-temperature growth or additional post-thermal treatment. However, both processes make it very difficult to form the p-type TiOx even under ...oxygen-poor growth condition. With the aid of high energy generated by high power impulse magnetron sputtering (HIPIMS), a highly stable p-type TiOx film with good quality can be achieved. In this research, by varying the oxygen flow rate, p-type γ-TiO and n-type TiO2 films were both prepared by HIPIMS. Furthermore, p- and n-type thin film transistors employing γ-TiO and TiO2 as channel layers possess the field-effect carrier mobilities of 0.2 and 0.7 cm2/Vs, while their on/off current ratios are 1.7 × 104 and 2.5 × 105, respectively. The first presented p-type γ-TiO TFT is a major breakthrough for fabricating the TiOx-based p-n combinational devices. Additionally, our work also confirms HIPIMS offers the possibility of growing both p- and n-type conductive oxides, significantly expanding the practical usage of this technique.
In this study, AgNWs@NiO–Co
3
O
4
nanocomposites were synthesized through the hydrothermal method and used as dopant materials for activated carbon-based supercapacitors. Self-synthesized ...one-dimensional silver nanowires (AgNWs) with a diameter of 500 nm were used to grow NiO and Co
3
O
4
on the AgNWs surface. The morphology and composition of the AgNWs@NiO–Co
3
O
4
nanocomposite material were analyzed. The experimental results revealed that doping of AgNWs@NiO–Co
3
O
4
nanocomposites can effectively increase the specific capacitance of supercapacitor. An ultrasonic spray coating was used to greatly reduce the weight of thin films, which were then employed to produce lightweight thin-film electrodes that induced the reaction with the electrolyte. The electrodes achieved a maximum specific capacitance of 706.95 F/g when activated carbon and AgNWs@NiO–Co
3
O
4
nanocomposites were mixed at a 10:1 ratio. Moreover, the charge transfer resistance decreased from 1.5 to 0.3 Ω. Even after 5000 cycles of charge and discharge tests, 92.81% of the capacitance was retained, which was higher than the capacitance of 65.19% retained in an undoped sample. These results demonstrated that the activated carbon thin-film electrode doped with AgNWs@NiO–Co
3
O
4
nanocomposites can effectively improve the capacitance and stability of the capacitor.
Abstract
The mechanism of carrier recombination in downsized μ-LED chips from 100 × 100 to 10 × 10 μm
2
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 SiO
2
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 μm
2
, 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 μm
2
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 μm
2
exhibited a high value of 516 nits at the voltage of 3 V.
In this study, high internal-quantum-efficiency (IQE) AlGaN multiple quantum wells (MQWs) were successfully demonstrated on low-defect-density AlN templates with nano-patterned sapphire substrates. ...These templates consisted of AlN structures with 0∼30 periods superlattices (SLs) by alternating high (100) and low (25) V/III ratios under a low growth temperature (1130 °C). Compared to conventional high crystal-quality AlN epilayers achieved at temperatures ≥1300 °C, lower thermal budget can reduce the production cost and wafer warpage. Via optimization of the SL period, the AlN crystallinity was systematically improved. Strong dependence of SL period number on the X-ray full-width-at-half-maximum (FWHM) of the AlN epilayer was observed. The AlN template with 20-period SLs exhibited the lowest FWHM values for (0002) and (10ī2), namely 331 and 652 arcsec, respectively, as well as an ultra-low etching pit density of 1 × 10
cm
. The relative IQE of 280 nm AlGaN MQWs exhibited a dramatically increase from 22.8% to 85% when the inserted SL increased from 0 to 20 periods. It has hardly ever been reported for the AlGaN MQW sample. The results indicate that the engineered AlN templates have high potential applications in deep ultraviolet light emitters.
Display omitted
•Al-doped ZnGa2O4 (ZGO) films were successfully prepared by co-sputtering.•High crystallinity along with excellent optical properties was achieved.•Deep-ultraviolet photodetectors ...(PD) fabricated with Al-doped ZGO films have been studied.•Al-doped ZGO PD exhibited remarkably high responsivity of 3.01 A/W at low bias of 3 V under the incident light of 220 nm.
Al-doped ZnGa2O4 (ZGO) films were deposited on c-plane sapphire substrates by co-sputtering of Al and ZGO targets at a substrate temperature of 400 ℃ and thermally annealed at 800 ℃ to enhance their crystalline quality. In this investigation, the DC power for metallic Al target was varied from 0 to 50 W and its effect on structural, optical, and optoelectronic properties of these films were investigated. After annealing, all films exhibited the crystalline nature with the ZGO phase. Further, this investigation revealed that the 800 ℃ annealed Al-doped ZGO film deposited with the 20 W DC power possessed the highest crystalline quality among other films along with the wide-bandgap of 5.18 eV. The X-ray photoemission spectrum measurements revealed from the Ga 2p3/2 and Al 2p core-level spectra that the Al atoms occupy the octahedral sites, which makes Al─O─Ga bonding in the ZGO network. The metal–semiconductor-metal photodetector with this annealed 20 W Al-doped ZGO film exhibited the photocurrent to the dark current ratio of 3.35 × 104 and high responsivity of 3.01 A/W (at 3 V and 220 nm), which shows the enhancement in device performance about 12 times when compared with that of annealed 0 W Al-doped ZGO photodetector.
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.
•Void formation on rear-side contacts of PERC cells affects conversion efficiency.•Smaller laser opening width and larger backside line spacing may form voids.•Higher laser ablation power resulted in ...barely dark region from EL measurements.•Efficiency of 22.25% for monocrystalline Si PERC solar cell was achieved.
The passivated emitter and rear cell (PERC), with advantages of reducing rear surface recombination and improving rear surface reflectivity, is extensively applied in monocrystalline and multicrystalline silicon solar cells. In this study, we investigated the rear PERC structure with various contact patterns (type I to VI) and line spacings (800–1000 µm) using 156.75 mm × 156.75 mm p-type Czochralski mono crystalline silicon wafers. The void formation on the rear-side contacts of PERC structures played an important role in affecting conversion efficiencies. A smaller laser ablated opening width may easily lead to the formation of voids under screen printing and co-firing backside aluminum. Further evidence from the electroluminescence (EL) measurements confirmed that the higher laser ablation power would result in a slightly dark region for the solar cell with a rear-side contact opening width greater than 45 µm. The type III backside contact pattern (dash 2:1) with a line spacing of 900 µm surpassed all other contact patterns owing to its excellent aluminum back surface field. As a result, by optimizing both the backside contact pattern and line spacing of PERC solar cells, the best conversion efficiency of 22.25% and 20.9% for the average PERC solar cells were achieved.
PDF
