Search

N-polar GaN-based blue-green light-emitting diodes (LEDs) with p-AlGaN electron blocking layer (EBL) were numerically investigated by simulation and experimentally grown on vicinal C-face SiC substrates by metal-organic chemical vapor deposition. By numerical simulation, we can find that p-AlGaN EBL in N-polar LEDs is able to play a more important role in blocking electron overflow than that in Ga-polar LEDs due to the reversed polarization, which leads to a high output power and internal quantum efficiency. Besides, the holes injection efficiency is enhanced in N-polar LED, resulting in a lower turn-on voltage. In experimental studies, N-polar LEDs based on different numbers of quantum wells were grown on vicinal C-face n-SiC substrates. When a forward bias is applied to the epitaxial N-polar LED with two quantum wells, a strong blue-green emission located at 480 nm can be observed. This work indicates that N-polar group-III nitrides have great potential in the application of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a strategy of combining the concepts of localized surface plasmons (LSPs) and core/shell nanostructure configuration in a single perovskite light‐emitting diode (PeLED) to addresses simultaneously the emission efficiency and stability issues facing current PeLEDs' challenges. Wide bandgap n‐ZnO nanowires and p‐NiO are employed as the carrier injectors, and also the bottom/upper protection layers to construct coaxial core/shell heterostructured CsPbBr3 quantum dots LEDs. Through embedding plasmonic Au nanoparticles into the device and thickness optimization of the MgZnO spacer layer, an emission enhancement ratio of 1.55 is achieved. The best‐performing plasmonic PeLED reaches up a luminance of 10 206 cd m−2, an external quantum efficiency of ≈4.626%, and a current efficiency of 8.736 cd A−1. The underlying mechanisms for electroluminescence enhancement are associated with the increased spontaneous emission rate and improved internal quantum efficiency induced by exciton–LSP coupling. More importantly, the proposed PeLEDs, even without encapsulation, present a substantially improved operation stability against water and oxygen degradation (30‐day storage in air ambient, 85% humidity) compared with any previous reports. It is believed that the experimental results obtained will provide an effective strategy to enhance the performance of PeLEDs, which may push forward the application of such kind of LEDs. [ABSTRACT FROM AUTHOR]

In this paper, N-polar GaN films with different V/III ratios were grown on vicinal C-face SiC substrates by metalorganic chemical vapor deposition. During the growth of N-polar GaN film, the V/III ratio was controlled by adjusting the molar flow rate of ammonia while keeping the trimethylgallium flow rate unchanged. The influence of the V/III ratio on the surface morphology of N-polar GaN film has been studied. We find that the surface root mean square roughness of N-polar GaN film over an area of 20 × 20 μm2 can be reduced from 8.13 to 2.78 nm by optimization of the V/III ratio. Then, using the same growth conditions, N-polar InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) were grown on the rough and the smooth N-polar GaN templates, respectively. Compared with the LED grown on the rough N-polar GaN template, dramatically improved interface sharpness and luminescence uniformity of the InGaN/GaN MQWs are achieved for the LED grown on the smooth N-polar GaN template. [ABSTRACT FROM AUTHOR]

The highly arrayed arsenic doped p-ZnO nanowires/ n-ZnO thin film homojunction light-emitting diode was fabricated on semi-insulated Si substrate. The homojunction was consisted of high-quality n-ZnO thin film grown by metal-organic chemical vapor deposition technology following arsenic doped ZnO nanowires grown by chemical vapor deposition. The device shows good rectification characteristic with a turn-on voltage of ~4.8 V and reverse breakdown voltage of ~18 V. Moreover, two distinct electroluminescence bands centered at 2.35 and 3.18 eV are detected from this device under forward bias at room temperature. [ABSTRACT FROM AUTHOR]

N-ZnO/GaO/ p-GaN heterojunction light-emitting diode (LED) was fabricated by metal-organic chemical vapor deposition. Compared with the n-ZnO/ p-GaN structure, the deep level visible emission at 525 nm was completely suppressed while UV emission at ~392 nm was significantly improved in ZnO/GaO/ p-GaN structure. The role of GaO in n-ZnO/GaO/ p-GaN heterojunction LED was discussed in detail. [ABSTRACT FROM AUTHOR]

Ultraviolet electroluminescence was demonstrated from a p-ZnO:As/n-SiC(6H) heterojunction light-emitting diode at room-temperature. The p-ZnO:As was fabricated by out-diffusion of arsenic atoms from a sandwiched GaAs interlayer on SiC substrate. The p-type doping was confirmed by both Hall and low-temperature photoluminescence measurements. Under forward bias, an intense ultraviolet emission centered at 384 nm was achieved from ZnO side of the diode. Furthermore, the light-output-current characteristic was determined to evaluate the high-efficiency electroluminescence performance of the diode. [ABSTRACT FROM AUTHOR]

The light-emitting diode of p-ZnO/n-GaAs heterojunction was grown by metal-organic chemical vapor deposition. The p-ZnO films have been formed by the doping As atoms which diffuse into ZnO film from GaAs substrate. The p-type behavior of As-doped ZnO films based on As-doped p-ZnO/n-GaAs, p-ZnO/p-GaAs heterojunction was studied by carrying out I-V measurements and x-ray photoelectron spectroscopy. The I-V characteristic of p-ZnO/n-GaAs heterojunction showed characteristic of rectifying diode and visual-infrared electroluminescence emission under forward current injection at room temperature. The I-V of the heterounction had a threshold voltage of ∼2.5 V. [ABSTRACT FROM AUTHOR]

Vertical conducting light-emitting diodes based on p-ZnO/n-GaN structure were fabricated on conductive n-SiC(6H) substrates. The p-ZnO:As films were prepared by arsenic out-diffusion from a sandwiched GaAs interlayer on a GaN/SiC template, and the AsZn-2VZn complex was considered to be the most probable defect contributing to the p-type conductivity of the ZnO:As films. Under forward bias, an intense ultraviolet emission at ∼384 nm from the ZnO side was observed. The electroluminescence performance of the diode was remarkable in terms of its low emission onset and high-purity ultraviolet emission. Additionally, the unencapsulated diode showed good stability over a duration of 2 months. [ABSTRACT FROM AUTHOR]

We fabricated the Ultraviolet light-emitting diode (LED) based on n-ZnO/i-NiO/p-Si heterostructure by metal-organic chemical vapor deposition (MOCVD). The device exhibited diode-like rectifying characteristics with a turn-on voltage of 3.2 V. The NiO film with high resistance state and [200] preferred orientation acted as an electron blocking layer, which produced a larger ZnO/NiO conduction band offset of 2.93 eV than that of ZnO/Si (0.30 eV). Under forward bias, prominent ultraviolet emissions peaked around 375 nm accompanying with rather weak blue–white emissions peaked around 480 nm were observed at room temperature. Furthermore, the mechanism of the electroluminescence was tentatively discussed in terms of the band diagram of the diode. [ABSTRACT FROM AUTHOR]

Xenon gas and mercury vapor based broad spectrum light sources have wide application, however, are hard to compact. On the contrary, LEDs are easy for compaction, but are hard to emit a broad spectrum. In this work, we demonstrate a simple phosphor free LED structure of ZnO/MgO/ITO, of which the spectrum covers the range from 300 to 650 nm. The device was fabricated on commercially available ITO substrate, and the ZnO/MgO structure was successively grown by MOCVD method, of which the morphology, crystallinity and optical quality were characterized. A thin MgZnO layer with graded composition is believed to form through the miscibility of MgO and ZnO during the initial growth stage of ZnO. The active region of the device includes the thin MgZnO layer and part of the subsequent grown ZnO layer. The light with wavelength shorter than ~360 nm is attributed to the near band edge emission of the MgZnO layer. And the near band edge emission and deep level emissions of ZnO contribute to the spectrum from ~360 to 650 nm. The working mechanism of the device is discussed mainly based on the energy band diagram. [ABSTRACT FROM AUTHOR]

The droop behaviors of two InGaN/GaN multiple-quantum-well blue-green light-emitting diodes grown on c-plane sapphires with different In content are investigated. The higher-In-content sample exhibits a lower efficiency, followed by a more significant droop as current increases in comparison with the lower-In-content diode. However, it is found that for both samples their efficiency reduction trend with increasing carrier density is nearly the same. Combining with the recombination rate equations, an analysis reveals that at the same injection current level, the carrier density in the higher-In-content quantum wells which have stronger polarization effect is larger due to the smaller bimolecular recombination coefficient, resulting in a more significant droop with current. Therefore, a study on the dependence of efficiency on carrier density can provide a clear elucidation to the physical mechanism of the efficiency droop behavior. [ABSTRACT FROM AUTHOR]

The n-InN/p-NiO/GaN heterojunction was fabricated by using plasma-assisted molecular beam epitaxy (PAMBE) combined with radio frequency magnetron sputtering. The device exhibited typical rectification characteristic with a turn-on voltage of ~1.5 V. Under forward bias, a dominant near infrared emission (NIR) peaked around 1565 nm was detected at room temperature. The NIR emission was attributed to the band-edge emission of InN film according to the photoluminescence spectrum of InN layer. Furthermore, the mechanism of the current transport and light emission was tentatively discussed in terms of the band diagrams of the heterojunction. [ABSTRACT FROM AUTHOR]

We fabricated the light-emitting diodes (LEDs) consisting of n-InN/p-NiO/p-Si heterostructure by using plasma-assisted molecular beam epitaxy (PAMBE) combined with radio frequency (RF) magnetron sputtering. The device exhibited diode-like rectifying current–voltage characteristics and had a turn-on voltage of 2.0 V. Under forward bias, a prominent narrow near infrared (NIR) emission peaked around 1565 nm was observed at room temperature. The NIR emission was demonstrated to come from the band-edge emission of InN layer. Moreover, the study of the LED in terms of the stability and efficiency were also discussed in detail. [ABSTRACT FROM AUTHOR]

Near-ultraviolet (UV) InGaN/AlGaN multiple quantum well (MQW) LEDs with 30 pairs AlGaN/GaN distributed Bragg reflectors (DBRs) were grown on 6H–SiC substrate by metal-organic chemical vapor deposition. A thin SiN x interlayer was introduced between the DBRs and n-GaN layer of the LED to reduce the threading dislocation density and result in enhancement the internal quantum efficiency ( η int ) of the InGaN/AlGaN LED. The result indicates that the light output power for the LED with DBRs and SiN x interlayer was approximately 56% higher (at 350 mA) than the LED without DBRs and SiN x interlayer on 6H–SiC substrate, and this significant improvement in performance is attributed not only to the light extraction enhancement via the DBRs but also due to improve epilayer crystalline quality. [ABSTRACT FROM AUTHOR]

Ultraviolet light-emitting diodes (LED) based on n-ZnO/NiO/p-GaN were realized by metal-organic chemical vapor deposition (MOCVD). The devices exhibited diode-like rectifying current–voltage characteristics and had a turn-on voltage of 7.5 V. High quality NiO film as an electron blocking layer inserted between the ZnO and GaN films showed high resistance state with preferred [1 1 1] orientation, which produced a larger ZnO/NiO conduction band offset of 2.93 eV than that of ZnO/GaN (0.15 eV). The electroluminescence spectra of the n-ZnO/i-NiO/p-GaN heterostructure demonstrated that electrons were effectively confined in the ZnO active region, and thus leading to the enhancement of the excitonic emission from the ZnO side. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, n-ZnO single microwire/p+-Si heterojunction LEDs are fabricated using the transparent conductive ITO film as an electrode. A distinct UV emission resulting from free exciton recombination in a ZnO single microwire is observed in the electroluminescence. Size difference of ZnO single microwire shows significant influence on emission efficiency. The EL spectra of n-ZnO single microwire/p-Si heterostructure exhibited relatively stronger UV emission which was compared with the EL spectra of n-ZnO single nanowire/p-Si heterostructure and n-ZnO film/p-Si heterostructure, respectively. [Copyright &y& Elsevier]

Abstract: A p-ZnO:N/n-GaN:Si structure heterojunction light-emitting diode (LED) is fabricated on c-plane sapphire by full metal organic chemical vapor deposition (MOCVD) technique. The p-type layer with hole concentration of 8.94×1016 cm−3 is composed of nitrogen-doped ZnO using NH3 as the doping source with subsequent annealing in N2O plasma ambient. Silicon-doped GaN film with electron concentration of 1.15×1018 cm−3 is used as the n-type layer. Desirable rectifying behavior is observed from the current–voltage (I–V) curve of the device. The forward turn on voltage is about 4V and the reverse breakdown voltage is more than 7V. A distinct ultraviolet (UV) electroluminescence (EL) with a dominant emission peak centered at 390nm is detected at room temperature from the heterojunction structure under forward bias conditions. The origins of the EL emissions are discussed in comparison with the photoluminescence (PL) spectra. [Copyright &y& Elsevier]

Abstract: In this paper, we proposed a new p-type ZnO doping method with metal organic chemical vapor deposition (MOCVD) technology by inserting a GaAs interlayer between substrate and ZnO epitaxial layer. The doping concentration of p-type ZnO film is able to be controlled by adjusting the thickness of the GaAs interlayer. With this method, we fabricated n-ZnO/p-ZnO:As homojunction light-emitting diode (LED) on ITO-glass substrate pre-coated with 20nm GaAs interlayer. The device exhibits a typical rectifying behavior by current–voltage (I–V) measurement. When the device is forward biased, UV–vis electroluminescence (EL) emissions can be observed clearly. [Copyright &y& Elsevier]

Abstract: ZnO film was firstly prepared by PA-MOCVD method on the substrate pre-coated with GaAs interlayer. Hall measurement found that the GaAs interlayer had important effects on the electrical behavior of the ZnO film. It could make the ZnO film convert to p-type conductivity. The XPS results confirmed that the acceptor was arsenic. And the acceptor level was 130meV above the ZnO valence band maximum. Low-temperature PL measurement was introduced to investigate the optical properties of both as-grown n-type and arsenic doped p-type ZnO films. Then, based on this technology, ZnO homojunction light emitting device (LED) was fabricated with arsenic doped p-type ZnO and unintentionally doped n-type ZnO on GaAs/p+-Si substrate. Its current–voltage (I–V) character showed a typical rectification behavior, which was different from the n-ZnO/p+-Si structure. The UV–visible (385–580nm) electroluminescence was detected under relatively low current injection condition from the n-ZnO/p-ZnO/p+-Si LED. [ABSTRACT FROM AUTHOR]

Abstract: Red and near-infrared (NIR) organic light-emitting devices (OLEDs) were fabricated based on Tetra (2-Isopropyl-5-methylphenoxyl) substituted metal-free phthalocyanine (Tetra-H2Pc). The devices were fabricated by vacuum deposition and spin coating methods. The electroluminescence (EL) intensity at about 910nm in the devices based on Tetra-H2Pc was increased by about 14 times compared with the intensity at about 930nm in the devices based on unsubstituted metal-free phthalocyanine (H2Pc) in the same device structures. The improvement in the EL intensity was attributed to the large steric hindrance of non-peripheral phenoxyl substituent of Tetra-H2Pc. It was found that the NIR EL spectra of the doped devices exhibited a strong dependence on the concentration of Tetra-H2Pc. The emission at 740nm was from Tetra-H2Pc monomer, while the emissions around 910nm and 870nm were from excimer or higher aggregated species. [Copyright &y& Elsevier]

Abstract: Heterojunction light-emitting diodes with ZnO/Si structure were fabricated on both high-resistivity (p) and low-resistivity (p+) Si substrates by metal–organic chemical vapor deposition technology. Fairly good rectifications were observed from the current–voltage curves of both heterojunctions. Ultraviolet (UV) and blue-white electroluminescence (EL) from ZnO layer were observed only from ZnO/p+-Si heterojunction under forward bias at room temperature (RT), while strong infrared (IR) EL emissions from Si substrates were detected from both ZnO/p-Si and ZnO/p+-Si heterojunctions. The UV and IR EL mechanisms have been explained by energy band structures. The realization of RT EL in UV–visible and IR region on Si substrate has great applicable potential for Si-based optoelectronic integrated circuits. [Copyright &y& Elsevier]