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The performance of photovoltaic systems is mostly determined by the materials used in their construction, regardless of the kind of application. We report on transparent broadband photodetectors based on p-Co3O4 and a heterojunction of n-ZnO, n-TiO2, or n-SnO2 that fits the needs of transparent optoelectronic devices. The heterojunction devices are fabricated by sputtering method. The energy band alignments are investigated with the aim of developing an efficient photodetector. The average transmittance values in the visible light range (400–800 nm) for TiO2, ZnO, and SnO2 are observed to be approximately 80%, 74%, and 66%, respectively. The current–voltage characteristics of the devices are also investigated and non-Ohmic characteristics are observed. Furthermore, a photovoltage study with post-rapid thermal processing (RTP) is carried out. It is found that enhancing the carrier lifetime is an efficient way to improve the performance of the devices. With an increased minority carrier lifetime, the transient photovoltage of the RTP-treated TiO2/Co3O4 device shows slow decay. [ABSTRACT FROM AUTHOR]

The p-GaN/N-Mg0.3Zn0.7O:In heterojunction photodiode is demonstrated in this study. The p-type GaN is grown using a hydride vapor phase epitaxy (HVPE) method and the n-type Mg0.3Zn0.7O:In thin film is deposited using a mist atmospheric pressure chemical vapor deposition (MAPCVD) method. The p-GaN/N-Mg0.3Zn0.7O:In photodiode shows a significant rectification ratio of $2.3 \times 10^{6}$ and high maximum responsivity of 0.93 A/W to UV-B. The significant UV-B to UV-A and UV-A to visible rejection ratios are found in the photodiode, which suggests that the p-GaN/N-Mg0.3Zn0.7O:In photodiode is capable of identifying visible light, UV-A, and UV-B. [ABSTRACT FROM AUTHOR]

An image sensor based on wide band gap silicon carbide (SiC) has the merits of high temperature operation and ultraviolet (UV) detection. To realize a SiC-based image sensor the challenge of opto-electronic on-chip integration of SiC photodetectors and digital electronic circuits must be addressed. Here, we demonstrate a novel SiC image sensor based on our in-house bipolar technology. The sensing part has 256 (16×16) pixels. The digital circuit part for row and column selection contains two 4-to-16 decoders and one 8-bit counter. The digital circuits are designed in transistor-transistor logic (TTL). The entire circuit has 1959 transistors. It is the first demonstration of SiC opto-electronic on-chip integration. The function of the image sensor up to 400 °C has been verified by taking photos of the spatial patterns masked from UV light. The image sensor would play a significant role in UV photography, which has important applications in astronomy, clinics, combustion detection and art.

In this article, a 4H-SiC metal-insulator-semiconductor-insulator-metal (MISIM) ultraviolet (UV) photodetector (PD) with a normal working temperature up to 550 °C, has been successfully fabricated and characterized for the first time. At 550 °C, the dark current of our fabricated MISIM remains at ~0.2 nA level and a record photo-to-dark current ratio (PDCR) of 62.7 is achieved at a reverse bias voltage of −15 V. Under 275 nm illumination, high responsivity (R) of 0.23 and 0.54 A/W have been achieved at room temperature (RT) and 550 °C, respectively. To the best of our knowledge, this is the best result reported for high-temperature UV detectors based on the 4H-SiC. This work is significant for developing high-temperature 4H-SiC-based UV PDs. [ABSTRACT FROM AUTHOR]

This article reported about the ultraviolet (UV) radiation effect on the resonance frequency response of a AT-cut piezoelectric quartz crystal. A large resonance frequency upshift was observed when the quartz crystal was irradiated by UV light of 355-nm wavelength using a Q-switched pulsed Nd:YVO4 UV laser. The dynamic frequency response behavior was systematically investigated by illuminating the quartz crystal with UV light in which the UV intensity was varied with time in staircase- and linear pulse-shaped patterns. From the experimental analysis, we measured the limit of detection and the sensitivity of the quartz crystal, which are about 0.5 mW/cm2 and 0.706 Hz/(mW/cm2), respectively. For a constant UV irradiation, a moderate response (<10 s) and recovery (<10 s) times were achieved during the on and off cycles of the UV light. The short-term repeatability and maximum operating limit of AT-cut quartz crystal were also further studied upon exposure to UV light with different intensities. In this work, we not only demonstrate the impact of UV irradiation on quartz crystal but also discuss the mechanism of upshift in resonance frequency upon exposure to UV light. This study shows the applicability of quartz crystal for the detection of UV light. [ABSTRACT FROM AUTHOR]

We report high-performance homojunction GaN avalanche photodiodes (APDs) grown on a low-defect GaN substrate and fabricated with an ion-implantation isolation method. High-quality p-i-n GaN layers were grown using metalorganic chemical vapor deposition (MOCVD), and an effective device isolation method using optimized nitrogen ion implantation was developed to provide significant leakage current suppression on the etched mesa sidewalls. Fabricated GaN APDs showed an ultralow dark current density < 10−9 A/cm2 up to 50% of the avalanching breakdown voltage region and achieved a photocurrent gain of >106 at a reverse bias of 71.5 V under deep-ultraviolet (DUV) illumination at λ = 280 nm. A further temperature-dependent study of the dark current indicated that a trap-assisted tunneling process predominates the leakage current component that also contributes to the carrier multiplication process near the avalanching breakdown. [ABSTRACT FROM AUTHOR]

In this paper, we propose a UV-A sensor based on a 6H-SiC Schottky photodiode with a thin Ni2Si front electrode and an integrated hydrogenated silicon nitride (SiN:H) dielectric filter. 6H-SiC prototypes were fabricated by using a manufacturing process to a large extent already implemented on 4H-SiC poly-type for the realization of a high signal-to-noise ratio ultraviolet (UV) sensor already commercialized. The results obtained on 6H-SiC prototypes show optimal electrical performance with dark current density lower than 0.2 nA/cm2 at room temperature and 10 V reverse bias. The use of 6H polytype allows shifting of the UV sensor response from 290 nm peak responsivity wavelength measured on standard 4H-SiC photodiodes to 360 nm wavelength in 6H-SiC prototypes with an integrated SiN:H filter exactly in the middle of the UV-A band (320-400 nm) with a simultaneous consistent reduction of the optical response in UV-C and UV-B regions below 320 nm wavelength.

N-polar AlxGa1−xN-based 365-nm ultraviolet (UV) light-emitting diodes (LEDs) with a hole-supplier layer composed of p-type Al0.2Ga0.8N/GaN superlattice (SL) doping or bulk doping structures are numerically investigated over Ga-polar UV-LEDs counterpart. The simulation results demonstrate that N-polar LEDs are favorable in mitigating the negative effect of the polarization-induced electric field. Thus, it exhibits superiority in promoting carriers confinement capability and suppressing electrons overflow over Ga-polar. As a result, the internal quantum efficiency, light output power, and electroluminescence intensity are significantly improved. In addition, both Ga-polar and N-polar devices exhibit the increased hole concentrations and higher radiative recombination rate within quantum wells after adopting SL p-doping structure. From the simulated energy band diagrams, the polarization-induced higher acceptor ionization rates at the heterostructure interfaces are observed. Evidently, the UV-LEDs based on N-polar SL p-doping structure are very effective to improve its performance, which is promising in achieving high-performance UV-LEDs of the future fabrication. [ABSTRACT FROM AUTHOR]

Front-illuminated GaN-based separate absorption and multiplication (SAM) ultraviolet (UV) avalanche photodiodes (APDs) with various photon detection areas are demonstrated grown by metalorganic chemical vapor deposition on bulk GaN native substrates with low dislocation density. By adopting a front-illuminated UV-APD structure with a thin AlGaN window layer, no additional etching of the substrate for the reduction of strong UV absorption is required. The epitaxial layer structure of the p-i-p-i-n SAM UV-APDs consists of a Mg-doped ${p}$ -Al0.05Ga0.95N window layer to minimize UV absorption at the top surface region and a Mg-graded ${p}$ -GaN charge layer to serve as a field-termination layer. The onset point of the breakdown voltage ( $V_{\text {BR}}$ ) is around 73 V for all SAM-APDs with different mesa areas ranging from 1963 to 10 $000~\mu \text{m}^{2}$ , which is a lower $V_{\text {BR}}$ than the typical p-i-n UV-APDs with the similar thickness of undoped layer, where the photon absorption and multiplication processes take place simultaneously. Under UV-light illumination at $\lambda =340$ nm, the SAM-APDs exhibit high avalanche gains greater than $8.0\times 10^{5}$ at a reverse bias of $V_{R}> 72.5$ V [ABSTRACT FROM AUTHOR]

High-efficiency high-voltage ultraviolet light-emitting diodes (HV-UVLEDs) consisting of a 4 × 4 microcells array with an area of 61 mil × 33 mil were designed and fabricated via the electrode pattern and interconnect technique. Polymer material was used to fill trench with planarization, and interconnection technology was used for metal layer connection to address wiring defect issue. In comparison with the conventional lateral UV-LED (C-UVLED), which had 33.6% and 34.7% enhancement in the light output power and wall-plug efficiency (at 1.5 W) of the HV-UVLEDs. A 56% improvement in the external quantum efficiency droop behavior was achieved for the HV-UVLEDs when compared with that of C-UVLED. This improvement can be attributed to superior current spreading in the HV-UVLED due to its smaller microcells, which increases light-emission efficiency overall. [ABSTRACT FROM PUBLISHER]

Anatase and rutile TiO2-based metal–semiconductor–metal (MSM) ultraviolet photodetectors (PDs) are fabricated and investigated. The TiO2 thin films are grown by the ultrasonic spray pyrolysis deposition and the TiO2 films are annealed at 400 °C and 800 °C to form the anatase and the rutile phases. The material characteristics were measured by X-ray diffraction, Raman spectrum, X-ray photoelectron spectroscopy, and photoluminescence. The optical characteristics such as refractive index, extinction coefficient, absorption coefficient, and optical reflectance were characterized. The electrical and optoelectronic characteristics of the anatase and rutile TiO2 MSM PDs were characterized, including current-voltage, Schottky barrier height, spectral responsivity, response time, and detectivity. [ABSTRACT FROM AUTHOR]

We developed a new method for using photoelectron-assisted chemical vapor deposition to deposit perfluoropolyether (PFPE) lubricant on a diamond-like carbon (DLC) overcoat. PFPE lubricant in the vapor phase was deposited on the DLC surface of a magnetic disk with a bias voltage between the disk surface and a counter electrode above the disk surface during ultraviolet irradiation. The bias voltage accelerated photoelectron emission from the DLC surface, and the photoelectrons partially dissociated the PFPE molecules in the vapor phase. The dissociated molecules then chemically bonded to the DLC surface. According to the experimental results, the bonded ratio of PFPE molecules to the DLC surface was approximately 100%. An ultrathin PFPE/DLC hybrid overcoat was produced as a monolithic film. This hybrid film exhibited a much lower surface energy than the reference Z-tetraol lubricant film and a high water contact angle of over 100°. This hybrid film can increase the head–media clearance and improve some read/write characteristics by using the actual heads. [ABSTRACT FROM AUTHOR]

In this paper, we propose a UV-A sensor based on a 6H-SiC Schottky photodiode with a thin Ni2Si front electrode and an integrated hydrogenated silicon nitride (SiN:H) dielectric filter. 6H-SiC prototypes were fabricated by using a manufacturing process to a large extent already implemented on 4H-SiC poly-type for the realization of a high signal-to-noise ratio ultraviolet (UV) sensor already commercialized. The results obtained on 6H-SiC prototypes show optimal electrical performance with dark current density lower than 0.2 nA/cm2 at room temperature and 10 V reverse bias. The use of 6H polytype allows shifting of the UV sensor response from 290 nm peak responsivity wavelength measured on standard 4H-SiC photodiodes to 360 nm wavelength in 6H-SiC prototypes with an integrated SiN:H filter exactly in the middle of the UV-A band (320–400 nm) with a simultaneous consistent reduction of the optical response in UV-C and UV-B regions below 320 nm wavelength. [ABSTRACT FROM PUBLISHER]

Dielectric barrier discharge (DBD) excimer lamps are efficient and environmentally friendly sources of ultraviolet (UV). One of the challenges for this technology to be massively adopted is the optimization and effective management of the overall lamp-supply system. Accordingly, a methodology to study the impact of the operating point over the performance and operation of a DBD UV excilamp is developed and experimentally validated. The DBD operating point is parametrically adjusted by means of the power supply current with three independent variables: intensity, frequency, and duty cycle. This methodology allows the determination of the optimal operating point for the particular excilamp under study. These supplying conditions will be later achieved by means of a dedicated electrical generator, which has to be especially designed according to these specifications. It is found that an increment in the current intensity has a positive impact on the lamp efficiency and also leads to the existence of more filamentary discharges. Also, a relation between the energy of the pulse supplied to the DBD and the reactor efficiency can be established. For certain levels of UV power, energy savings on the reactor higher than 50% are attained by proper selection of the operating point. [ABSTRACT FROM PUBLISHER]

This work uses ultrasonic spray pyrolysis deposition to grow titanium dioxide and aluminum oxide (Al2O3) films, respectively, as an active layer and an insulator layer of the metal–insulator–semiconductor–insulator–metal (MISIM) photodetector (PD). 10-, 20-, and 30-nm-thick Al2O3 films were deposited and the I – V characteristics in the dark and under illumination were measured and investigated. The dark current was suppressed to 11.6 pA for the MISIM PD with the 30-nm Al2O3. In addition, the carrier transportation mechanisms of the dark current are analyzed. The photoresponsivity of the MISIM PD with the 10-nm Al2O3 was 8.22 A/W (at 10 V), which is much higher than 0.84 A/W of the metal-semiconductor–metal PD. The noise equivalent power and detectivity of the MISIM PD with the 10-nm Al2O3 were 2.28\times 10^-10 W and 2.4\times 10^9 Jones. The PDs showed a slight degradation when the ambient temperature was up to 450 K. [ABSTRACT FROM AUTHOR]

The band-engineered structure design for electron-blocking layer (EBL) and hole-blocking layer (HBL) in AlxGa1–xN-based ultraviolet light-emitting diodes (UV LEDs) is performed and analyzed theoretically. Simulation results show that the severe polarization effect is efficiently mitigated and the downward-bended band profile of the EBL is improved when the EBL is designed with a graded-composition and multiquantum barrier (GMQB) structure. As a result, the capabilities of both electron confinement and hole injection, and also the light output power are promoted. On the contrary, for the HBL, the design of composition graded and/or multiquantum barrier structures reduces the effective potential barrier height for holes in the valence band and, consequently, causes a considerable hole overflow. The UV LED, thus, exhibits superior optical performance when the LED structure is simultaneously designed with a GMQB EBL and a bulk HBL. [ABSTRACT FROM PUBLISHER]

A light-emitting diode (LED) consisting of an ultraviolet (UV) InGaN/AlGaN multiple quantum-well (MQW) p-i-n structure and a ten-pair green unipolar InGaN/GaN MQW grown on the same sapphire substrate was investigated. After a series of device-processing procedures, including wafer bonding and laser liftoff, the proposed UV LED structure, which features a visible indicator formed through selective-area photon recycling and exhibiting a dual-peak spectrum comprising UV and green peaks, was produced. The green peak originated from UV light generated by the electrical pumping of the epitaxially stacked green MQW. The green light emission may practically be used in indicators and warning signs during the operation of UV LEDs. The current-dependent light output of the green peak may further serve as a reference for measuring the output power of the UV peak of the proposed UV LEDs. [ABSTRACT FROM PUBLISHER]

This paper uses nonvacuum ultrasonic spray pyrolysis deposition method to grow TiO2 for ultraviolet (UV) detection. The analyses of the materials like X-ray photoelectron spectroscopy, X-ray diffraction, and photoluminescence were investigated. The 600 °C annealing temperature is the optimum condition to obtain the anatase TiO2. The metal–semiconductor–metal (MSM) photodetectors (PDs) with 3-, 5-, 7-, 10- \mu \textm finger spacing were fabricated and the performance was investigated. The PD with 10- \mu \textm finger spacing has the lowest dark current of 2.92\times 10^-11 A and the highest UV-to-visible rejection ratio ( $R_{{{{\rm UV}/{\rm VIS}}}}) of 2.1\times 10^5 at 5 V. The PD with 5- \mu \textm finger spacing has the lowest noise equivalent power of 2.57\times 10^-9 W and the highest detectivity ( D^\ast ) of 5.46\times 10^{8} cmHz ^{0.5}\text{W}^{-1}$ . The rising time and the falling time of the PD are 5 and 12 s. In addition, the TiO2-based MSM PD in this paper operated normally at 450 K; however, the performance is slightly degraded. The mechanisms causing degradation at high temperature were investigated. [ABSTRACT FROM AUTHOR]

This paper proposes the H2O2 oxidation technique to grow Al2O3 as the surface passivation layer of the metal–semiconductor–metal ultraviolet (UV) photodetector (PD). The dark current of the H2O2-grown-Al2O3-passivated PD was reduced from 104 to 4.43 nA. The surface leakage of the PD was reduced from 65.7 nA/ 1.67~\mu \textA to 0.46 nA/0.5 nA in the dark/under illumination. It was found that $\sim 35$ % photocurrent results from the surface leakage. The surface leakages in the H2O2-grown-Al2O3 passivated and the plasma-enhanced chemical vapor deposition (PECVD)-grown-SiO2 passivated PDs were reduced significantly. Although the photocurrent and the photoresponsivity of the oxide-passivated PDs were lower than those of the unpassivated one, the dark current, UV-to-visible rejection ratio, noise equivalent power, and the detectivity of the oxide-passivated PDs were better than those of the unpassivated one. In addition, the performances of the H2O2-grown-Al2O3 passivated PD were better than those of the PECVD-grown-SiO2 passivated one. [ABSTRACT FROM PUBLISHER]

Colloidal quantum dots (QDs) with a ZnO core were synthesized with subsequent surface passivation by MgO. The photo-enhancement effect of the near band-edge photoluminescence (PL) in ZnO nanocrystals, dispersed in ethanol, is investigated by observing changes in the optical properties after ultraviolet (UV) exposure. Finally, the operation as a light-emitting device (LED) was demonstrated experimentally for these ZnO-based quantum dots (QDs). The results indicate that this type of QDs might enable the development of electroluminescent UV sources in the near future. [ABSTRACT FROM PUBLISHER]

In this paper, the thickness effect of an undoped Al0.23Ga0.77N inserted in the Mg-doped Al0.23Ga0.77N electron-blocking layer (EBL) on the characteristics of the ultraviolet light-emitting diodes (UV-LEDs) was analyzed. The results of secondary-ion-mass spectrometry clearly show that the concentration of Mg back-diffusion from the p-GaN and the Mg-doped EBL decreases with the thickness of an undoped EBL. The radiative recombination rate in the multiple quantum wells (MQWs) can be obviously enhanced after inserting an undoped EBL from the simulated results, and the sample with a 6-nm-thick undoped EBL has the highest radiative recombination rate. It is worth noticing that the hole carrier concentration in the MQWs increases with increasing the thickness of an undoped EBL. The UV-LED possesses 400% enhancement in the output power (at 20 mA) by inserting a 6-nm-thick undoped EBL. The significant enhancement is ascribed to the decrease of nonradiative recombination defects formed by Mg atoms and the increase of hole concentration in the MQWs. [ABSTRACT FROM AUTHOR]

A single-photon avalanche diode with high sensitivity in the ultraviolet (UV) wavelength range has been fabricated on Si using pure boron chemical vapor deposition to create both a nanometer-thin anode junction and a robust light entrance window. The device shows high sensitivity at the wavelengths of 330–370 nm when operated in the Geiger mode and good selectivity for UV light without applying a capping filter. The dark count rates can be as low as 5 Hz at room temperature for an active area of \(7~\mu \) m \(^{2}\) . An implicit guard ring, using an n-enhancement implantation in the central region of the diode, is applied instead of peripheral diffused p-type guard rings to achieve a high fill factor. [ABSTRACT FROM AUTHOR]

ZnO nanowalls are rapidly grown on a glass substrate using a low-temperature thermal evaporation method, without the use of a catalyst and the pre-deposition of a ZnO seed layer on the substrate. Most of the ZnO nanowalls are grown vertically and are about 70–200-nm thick and 2-\mum long. The room-temperature photoluminescence spectra show a strong intrinsic ultraviolet (UV) emission and a weak defect-related orange emission. The ZnO nanowall UV sensor is highly sensitive to UV light, with an excellent UV-to-visible ratio and good flicker noise characteristics. This shows the strong potential of ZnO nanowalls for use in UV sensors. At an applied bias of 2 V, the noise equivalent power and the normalized detectivity of the ZnO nanowall UV sensor are 1.87\times 10^-10~W and 3.38\times 10^9~cm\cdotHz^0.5\cdotW^-1, respectively. [ABSTRACT FROM PUBLISHER]

A XeCl dielectric barrier discharge (DBD) excilamp applied by pulsed and sinusoidal voltage waveforms is simulated using a 1-D drift–diffusion model. In both waveforms, the light output power depends not only on the gas mixture composition but also on the electrical parameters of each voltage waveform such as the frequency, the duty cycle, etc. At the same amplitude of the applied voltage and frequency, the light ultraviolet output efficiency of a pulsed voltage is higher than that of a sine voltage. These results obtained in this paper permit us to find out an appropriate power supply for a DBD excilamp. [ABSTRACT FROM AUTHOR]

Organic ultraviolet photodetectors (PDs) with a narrow-band spectral response are fabricated. TAPC and PBD were utilized as the electron donor and acceptor, respectively. Glass/indium tin oxide (ITO) was employed as the anode contact and the incident light window. The PDs reveal a narrow response width of 30 nm at 316–346 nm. A peak response of 0.12 A/W at 330 nm and a photo-to-dark ratio of about \1.1 \times \10^2 under 330-nm light illumination with an intensity of 0.95 \mW/cm^2 were achieved. The realization of the narrow-band response should be ascribed to the steep absorption of organic materials at the long wavelength and the blocking role of glass/ITO contact at the short wavelength. [ABSTRACT FROM AUTHOR]

High-density vertical ZnO nanowires (NWs) were synthesized by vapor phase transport deposition without a metal catalyst or template. The work function \phi of ZnO NWs was reduced to 3.7 eV by exposure to UV. At a low vacuum of 10^-3 Torr, the UV light improved the field emission performance and reduced the turn-on voltage such that they were better than those of normal field emission in a high vacuum. The depletion layer of NWs disappeared because surface O_2^ - oxygen molecules were removed by exposure to UV light. The enhancement by UV remained even after the UV light had been turned off for 20 min. [ABSTRACT FROM PUBLISHER]

Inspections and diagnoses of corona discharges are important in order to prevent electrical faults of external insulation in power systems. This paper studies the measurement of ultraviolet rays (UV) strength of corona discharges on polymer insulators using a UV sensor with an optic lens. The data have been compared with the images of a UV camera. The UV signal by corona discharge was detected from more than 60 kV, which was equivalent to around 37.5% of the breakdown voltage. The UV strength increased with increasing high voltage and the supplying dc voltage. Also, UV image was observed. However, the longer the distance was, the greater the reduction in UV signals would be. The robust, inexpensive sensor can detect corona discharge activity on polymer insulators when the applied voltage exceeds 37.5% of the breakdown voltage. [ABSTRACT FROM AUTHOR]

We fabricated and characterized ultraviolet (UV) light-emitting diodes (LEDs) composed of n-ZnO/SiO2-ZnO nanocomposite/p-GaN heterostructures. Significant UV electroluminescence at 387 nm from the n-ZnO layer in this heterostructure LED was observed at a forward-bias current of as low as 1.8 mA. This is ascribed to the high quality of the n-ZnO layer and the effective function of the SiO2-ZnO nanocomposite layer. The SiO2-ZnO nanocomposite layer accomplishes the role of current blocking by forming the larger energy barrier for electron injection from n-ZnO into p-GaN and also contributes to, due to its low refractive index, higher light extraction efficiency from the n-ZnO layer. [ABSTRACT FROM AUTHOR]

By using a novel negative-tone photoresist, KMPR, we have investigated ultraviolet (UV) lithographic microelectroforming fabrication of ultrathick metallic microstructures (≥ 400 µm). Scanning coating spin speed together with the film thickness and uniformity has been characterized at low spin speed from 1000 to 200 r/min. Based on the film profile characterization, the single-spin lithography conditions for a 400-µm-thick electroforming mold are optimized by scanning process parameters of UV exposure energy and bake temperature and time. SEM-measured dimensional accuracy and sidewall verticality of the optimized thick KMPR mold are Δ ≤ 3 µm and 90° ± 1°, respectively, which are comparable to those of SU8 molds. The SEM analysis of the patterned film and the electroformed structure has shown that the submillimeter-thick KMPR features have ~5-10 : 1 aspect ratio. The sidewall surface roughness of the copper deposition is locally measured to be about ~50-100 nm by atomic force microscopy, which is significantly smoother than that resulting from other mechanical machining approaches. This novel photoresist enables the lithographic molding microfabrication process to mass produce plastic and metallic microcomponents for various microelectromechanical systems applications. [ABSTRACT FROM AUTHOR]

The potential of using water-vapor plasmas excited by microwaves as a ultraviolet (UV) light source has been investigated by using various pressures and input powers. The UV irradiation power increased and saturated at a pressure range dependent on the input power. On the other hand, other visible and infrared emissions corresponding to four atomic lines, i.e., the Balmer series of hydrogen at 486.1 nm (Hβ) and 656.3 nm (Hα) and oxygen atoms at 777.2 and 844.6 nm, were clearly decreased with an increase in the total gas pressure. It was found that pressures (1.4-2.0 kPa) near the saturated water-vapor pressure were found to give the most intense UV irradiation. With a vapor pressure of 1.6 kPa and a total microwave power of 300 W, the power density of UV (Γuv) was measured to be 10.5 µW · cm-2 at a distance of 30 cm from the center of the discharge tube as measured through an optical viewing port on the cavity discharge applicator. This value for (Γuv) is comparable to that for a mercury lamp. However, the (ηuv) efficiency was estimated to be considerably lower than that of a mercury lamp. [ABSTRACT FROM AUTHOR]

GaN-based ultraviolet (UV) photodetectors (PDs) separately prepared with a conventional single low-temperature (LT) GaN buffer layer and a 12-pair MgxNy-GaN buffer layer were both fabricated. It was found that we could reduce threading dislocation (TD) density and thus improve crystal quality of the GaN-based UV PDs by using the 12-pair MgxNy-GaN buffer layer. With a -2-V applied bias, it was found that the reverse leakage currents measured from PDs with a single LT GaN buffer layer and that with a 12-pair MgxNy-GaN buffer layer were 4.57 × 10-6 and 1.44 × 10-12 A, respectively. It was also found that we could use the 12-pair MgxNy-GaN buffer layer to suppress photoconductive gain, enhance UV-to-visible rejection ratio, reduce noise level, and enhance the detectivity. [ABSTRACT FROM AUTHOR]

This paper analyzes the performance and reliability of deep-ultraviolet light-emitting diodes (LEDs) on AlGaN emitting at 280 and 295 nm. By means of detailed electroluminescence characterization, we show that the optical properties of the LEDs are strongly influenced by the presence of deep-level-related radiative transitions, and we separately evaluate the contribution of each of these recombination mechanisms on the overall light emission. The reliability analysis presented in this paper shows that stress determines the gradual decrease of the output power of the LEDs, which is more prominent at low measuring current levels. Degradation is attributed to the increase of the nonradiative recombination rate. By means of C-V analysis, we give evidence of modifications of the charge distribution in the active layer, taking place as a consequence of stress: this mechanism is considered to be related to the generation of new defect states near/within the active region. [ABSTRACT FROM PUBLISHER]

We report 4H-SiC p-i-n avalanche photodiodes (APDs) with very low dark current. When biased for a photocurrent gain M of 1000, a 100-μm-diameter device exhibits dark current of 5 pA (63 nA/cm2), corresponding to primary multiplied dark current of 5 fA (63 pA/cm2). The peak responsivity at unity gain is 93 mA/W (external quantum efficiency = 41%) at λ = 280 nm. The excess noise factor corresponds to k = 0.1. Detection of several tens of femtowatts of ultraviolet light is reported. [ABSTRACT FROM AUTHOR]

Here, we present the characteristics of a novel GaN- based ultraviolet (UV) photodiode (PD) with a low-temperature (LT) AIN cap layer. The dark leakage current for the PD with the LT-AIN cap layer was shown to be about four orders of magnitude smaller than that for the conventional PDs. It was found that we could achieve larger UV to visible rejection ratio by inserting an LT-AIN cap layer. It was also found that we could improve minimum noise equivalent power and maximum normalized detectivity of the PD by inserting an LT-AIN cap layer. [ABSTRACT FROM PUBLISHER]

In this letter, the ultraviolet light emitting diode (UV-LED) with an undoped Al0.23Ga0.77N electron-blocking layer (EBL) between the p-type doped Al0.23Ga0.77N EBL and last barrier was proposed. After inserting the undoped EBL, both the photoluminescence and electroluminescence (EL) characteristics of UV-LED were significantly improved. As the undoped EBL was inserted, the 365-nm UV-LED possessed 400% improvement in output power (at 19 A/cm^2). However, the enhancement in output power was significantly reduced to 20% when the insertion of undoped EBL was applied for 375-nm UV-LED. In addition, the long-term reliability was enhanced efficiently with the addition of undoped EBL. After the aging test for 1032 h, it presented the 365-nm UV-LED inserted with an undoped EBL had the obvious improvements both in the characteristics of EL intensity and leakage current density. [ABSTRACT FROM AUTHOR]

In this letter, uniform NaTaO3 microcube films were synthesized on tantalum foils by a facile low temperature hydrothermal method. The capacitance characteristic of the film was demonstrated by Mott–Schottky measurement. Then, ultraviolet (UV) detector based on NaTaO3 film was fabricated with Ag electrodes. At 5 V reverse bias, the current was 20.2 nA under the irradiation of 260-nm UV light, which is 13 times larger than that under dark condition (1.5 nA). The displacement current was observed in the device due to large capacitance existing between Ag electrodes and NaTaO3 film. The devices show a rise time of 4.6 s and a decay time of 15.4 s. These studies suggest the potential application of NaTaO3 film in fabricating UV detectors with low power dissipation. [ABSTRACT FROM PUBLISHER]

Semiconducting amorphous indium-gallium-zinc oxide (a-IGZO) films are integrated with an Al2O3/Pt-nanocrystals/Al2O3 gate-stack to form UV-erasable thin-film transistor (TFT) memory. The threshold voltage (Vth), subthreshold swing, ION/IOFF ratio, and effective electron mobility of the fabricated devices are 2.1 V, 0.39 V/decade, \sim10^6, and 8.4 cm^2/V\cdots, respectively. A positive Vth shift of 2.25 V is achieved after 1-ms programming at 10 V, whereas a negative Vth shift as large as 3.48 V is attained after 5-s UV erasing. In addition, a 10-year memory window of 2.56 V is extrapolated at room temperature. This high-performance a-IGZO TFT memory is suitable for optical touch-panel applications. [ABSTRACT FROM PUBLISHER]

A ZnO/ZnMgO multiple-quantum-well ultraviolet (UV) random laser diode was fabricated on a commercially available n-type GaN wafer using a radio frequency magnetron sputtering system. The electroluminescence measurements revealed that the diode exhibited fairly pure UV random lasing centered at \sim370 nm under sufficient forward bias at room temperature. The full-widths at half-maximum of the sharp lasing peaks are less than 0.4 nm. The device has a very low threshold current density of 4.7 \A/cm^2 and extremely weak visible emission. [ABSTRACT FROM AUTHOR]

A ZnO-based metal-insulator (HfO2)-semiconductor diode was synthesized on a commercially available n+-GaN/sapphire substrate using a radio-frequency magnetron sputtering system. Electroluminescence measurements revealed that the diode exhibited fairly pure ultraviolet (UV) emission peaking at ∼370 am with a line width of less than 8 nm. By choosing a proper thickness of the insulator HfO2 layer, the threshold voltage of the emission could be reduced to 2 V, demonstrating that this ZnO-based fairly pure UV light-emitting diode can be driven by two ordinary dry batteries. The reason for low threshold voltage is proposed in terms of the n+-GaN/sapphire substrate and the high-k insulator HfO2 layer. [ABSTRACT FROM AUTHOR]

We fabricated and investigated the performances of InGaN-AlGaN ultraviolet (UV) light-emitting diodes (LEDs) emitting at 380 nm. The output power of a conventional LED, a patterned sapphire substrate LED (PSS LED), and a PSS flip-chip LED (PSS FCLED) were about 0.94, 1.86, and 5.18 mW, respectively, at a forward injection current of 20 mA. These results indicate that the light output-powers of the PSS LED and PSS FCLED were enhanced as much as 97% and 451% compared to the conventional LED. Subsequent optical simulations confirm the remarkable enhancements in optical power of the PSS FCLED at UV wavelengths. [ABSTRACT FROM PUBLISHER]

In this study, we proposed and realized a nitride-based Schottky barrier sensor module with high electrostatic discharge (ESD) reliability. By including a Si-based ESD protection chip into the module, we can significantly enhance endurable ESD voltages under both forward and reverse human-body-mode (HBM) ESD stresses. It was found that the fabricated module can endure reverse HBM ESD stress of 7.5 KV and forward HBM ESD stress larger than 8 KV. It was also found that the inclusion of the Si-based ESD protection chip will not result in a decrease in detector responsivity [ABSTRACT FROM PUBLISHER]

We report electrical and electrooptical characteristic of mesa-structure 6H-SiC PIN avalanche photodiodes. At a gain of 1000, the dark current density is 9.2 muA/cm2. The excess noise factor corresponds to a k value of ~0.1. In addition, peak responsivity of 80 mA/W was observed at 290 nm (external quantum efficiency of ~35%) [ABSTRACT FROM PUBLISHER]

In this study, Al-doped ZnO (AZO) Ni-AZO and NiOx--AZO films were deposited on p-type GaN films. The depositions were followed by thermal annealing to form Ohmic contacts. The p-GaN-AZO contacts exhibited a non-Ohmic electrical characteristic. However, electrical characteristic could be greatly improved by insertion of Ni or NiOx between AZO film and p-GaN layer. In case of 1×1 mm2 ultraviolet light-emitting diodes (LEDs) with Ni-AZO contacts, the light output approached saturation point when the injection current was about 400 mA. However, the saturation point was as high as 500 mA for the LEDs with NiOx--AZO contacts. The lower saturation point could be due to the fact that the resistivity of Ni-AZO films was higher than that of NiOx--AZO films, thus leading to a severe current crowding effect. The increased resistivity of the Ni-AZO films could be attributed to the interdiffusion between Ni and AZO films. When compared to the LEDs with Ni-Au Ohmic contacts, the light output of the LEDs with Ni-AZO and NiOx--AZO contacts was higher by 38.2% and 60.6% at 350 mA, respectively. [ABSTRACT FROM PUBLISHER]

We report ultraviolet separate absorption and multiplication 4H-SiC avalanche photodiodes. An external quantum efficiency of 83% (187 mA/W) at 278 nm, corresponding to unity gain after reach-through was achieved. A gain higher than 1000 was demonstrated without edge breakdown. [ABSTRACT FROM PUBLISHER]