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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]

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]

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]

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]

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]

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]

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]

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]