Dual-wavelength Light-emitting Diodes Research Articles

Advantage of dual wavelength light-emitting diodes with dip-shaped quantum wells

Dual-wavelength light-emitting diodes (DW-LEDs) with dip-shaped quantum wells have been studied by numerical simulation. The emission spectra, light output power, carrier concentration in the quantum wells and internal quantum efficiency are investigated. The simulation results indicate that the DW-LEDs with dip-shaped quantum wells perform better than conventional LEDs with rectangular quantum wells in terms of light output power, leakage current and efficiency droop. These improvements in the electrical and optical characteristics are mainly attributed to the alleviation of the electrostatic field in the dip-shaped quantum wells.

Investigation of spectral regulation in dual- wavelength light-emitting diodes by using the selective p-doped barriers

The electrical and the optical characteristics of dual-wavelength light-emitting diode (LED) with the newly designed selective p-doped barriers are investigated numerically. The simulation results show that the selective p-doped barriers can improve the distribution equilibria of electron and hole concentrations in each quantum well (QW). The radiative recombination rate of QW is enhanced remarkably when specific number of p-doped barriers is adopted, and the electron leakage current is suppressed obviously with this new design. Therefore, the internal quantum efficiency is improved and the trend of efficiency drooping with the increase of current injection is also alleviated. Moreover, the curve peaks of the spectrum become quite uniform when the specific number of vertically-stacked QWs is adopted, and the spectral regulation of the dual-wavelength LED is more effective.

Investigation of GaN-based dual-wavelength light-emitting diodes with p-type barriers and vertically stacked quantum wells

Designs of p-doped in quantum well (QW) barriers and specific number of vertically stacked QWs are proposed to improve the optical performance of GaN-based dual-wavelength light-emitting diodes (LEDs). Emission spectra, carrier concentration, electron current density, and internal quantum e±ciency (IQE) are studied numerically. Simulation results show that the e±ciency droop and the spectrum intensity at the large current injection are improved markedly by using the proposed design. Compared with the conventional LEDs, the uniform spectrum intensity of dual-wavelength luminescence is realized when a specific number of vertically stacked QWs is adopted. Suppression of electron leakage current and the promotion of hole injection e±ciency could be one of the main reasons for these improvements.

Effect of an asymmetry n-AlGaN layer on performance of dual-blue wavelength light-emitting diodes

The effect of an n-type AlGaN layer on the physical properties of dual-wavelength light-emitting diode (LED) is investigated numerically. The simulation results show that compared with the conventional p-type AlGaN electron-blocking layer (EBL), the n-type AlGaN layer can improve the distribution of electrons and holes more uniformly and realize the radiation balance between electrons and holes in the quantum wells, and further reduce the efficiency dro of dual-blue wavelength LED at high current. In addition, the spontaneous emission rate of two kinds of quantum wells can be adjusted through the control of Al composition. It can be found from the results that the emission spectrum of dual-blue wavelength LED is more stable at low current with an Al composition of 0.16, while the emission spectrum is more stable at high current with an Al composition of 0.12.

The investigation of performance improvement of GaN-based dual-wavelength light-emitting diodes with various thickness of quantum barriers

The electrical and optical characteristics of GaN-based dual-wavelength light-emitting diodes (LEDs) with the specific design of various thick barriers are investigated numerically. The simulation results show that the thickness of barrier plays a regulatory role in emission spectrum of the dual-wavelength LED. The internal quantum efficiency droop is improved and the two peaks of spectrum become uniform due to the thickness of barriers gradually decreasing from the n-side to the p-side in a specific way. The balanced distribution of carrier concentration and the enhancement of electron confinement could be the major physical mechanism behind these improvements. It is also shown that the better optical performance is achieved at the large current injection level.

Comparison of nitride-based dual-wavelength light-emitting diodes with an InAlN electron-blocking layer and with p-type doped barriers

The advantages of nitride-based dual-wavelength light-emitting diodes (LEDs) with an InAlN electron blocking layer (EBL) are studied. The emission spectra, carrier concentration in the quantum wells (QWs), energy band and internal quantum efficiency (IQE) are investigated. The simulation results indicate that an LED with an InAlN EBL performs better over a conventional LED with an AlGaN EBL and an LED with p-type-doped QW barriers. All of the advantages are due to the enhancement of carrier confinement and the lower electron leakage current. The simulation results also show that the efficiency droop is markedly improved and the luminous intensity is greatly enhanced when an InAlN EBL is used.

Investigation of the Carrier Distribution Characteristics in InGaN Multiple Quantum Wells by Using Dual-wavelength Light-emitting Diodes

Investigation of the Carrier Distribution Characteristics in InGaN Multiple Quantum Wells by Using Dual-wavelength Light-emitting Diodes

Effect of spectrum-control in dual-wavelength light-emitting diode by doped GaN interval layer

A two-dimensional simulation of electrical and optical characteristics of dual-wavelength LED (light-emitting diode) with doped GaN interval layer is conducted with software.It shows that by the use of doped GaN interval layer, we can solve the luminescence intensity disparity of the two kinds of quantum wells in dual-wavelength LED. And through control of the thickness of the interval layer, we can adjust the relative luminescence intensity of the two kinds of quantum wells. Therefore, the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of holes or electrons by doped GaN interval layer.

双波长InGaN/GaN多量子阱发光二极管的光电特性

In order to realize preferable white light-emitting diodes with high color rendering index and optimized luminous efficiency,white InGaN/GaN multi-quantum-well dual-wavelength light-emitting diodes(LEDs) were grown on(0001)-oriented sapphire substrates by metal-organic chemical vapor deposition(MOCVD).Photoluminescence and electroluminescence properties of dual-wavelength LEDs with different In content were also studied.The experimental results indicated that In component plays a critical role on stability for electroluminescence spectrum and luminous efficiency of the dual-wavelength LED structures.In addition,YAG∶Ce phosphor-converted white light emission with high color rendering index was achieved using dual-blue emitting active regions.

Luminescence properties of blue and green dual wavelength InGaN/GaN multi-quantum well light-emitting diode

Blue and green dual wavelength InGaN/GaN multi-quantum well (MQW) light-emitting diode (LED) has wide applications in full color display, monolithic white LED and solid state lighting, etc. Blue and green dual wavelength LEDs, which consist of InGaN strain-reduction layer, green InGaN/GaN MQWand blue InGaN/GaN MQW, were grown by metal-organic chemical vapor deposition (MOCVD), and the luminescence properties of dual wavelength LEDs with different well arrangements were studied by photoluminescence and electroluminescence. The experimental results indicated that well position played an important role on the luminescence evolvement from photoluminescence to electroluminescence.

Four-Wavelengths-Mixed White Light Emitting Diodes with Dual-Wavelength-Pumped Green and Red Phosphors

The wavelengths of dual-wavelength light-emitting diodes (LEDs) are near ultraviolet (UV) at approximately 409 and 459 nm for blue when driven at 20 mA. The near-UV emission intensity of LEDs is stronger than the blue emission intensity with a 20 mA driven current. The green and red emission intensities of the phosphor are almost the same as, but less than, the blue emission intensity of the dual-wavelength LED with a 20 mA driven current. The CIE color coordinates are x=0.32 and y=0.35, while the dual-wavelength LED with a green and red phosphor LED lamp is driven at 20 mA.

Barrier effect on hole transport and carrier distribution in InGaN∕GaN multiple quantum well visible light-emitting diodes

Carrier distributions governed by hole transport in InGaN∕GaN multiple quantum well (MQW) visible light-emitting diodes (LEDs) were investigated using conventional blue LEDs and dual-wavelength blue-green LEDs. It was found that holes were dominantly distributed in the QW close to the p-GaN layer in LEDs with conventional MQW active regions at a current of 20mA. A decrease in the thickness or the height of the quantum-well potential barrier enhanced hole injection into the MQWs located near the n-GaN layer. Reducing the thickness of a GaN quantum-well barrier between the blue QW and green QW did not degrade the electroluminescence (EL) intensity of the LED. In contrast, reducing the potential height of the barrier with material of possibly compromised quality resulted in a degradation of the EL intensity of the LED.

Can CQ Be Completely Replaced by Alternative Initiators in Dental Adhesives?

Despite good clinical acceptance, photoinitiating systems based on camphorquinone and amines raise concerns in terms of yellowing, aging, toxicity, or degradation in low pH conditions. This study aimed to prove whether CQ could be successfully replaced by alternative initiators in adhesive systems. Further, the efficiency of a prototype dual-wavelength LED (= Light Emitting Diode) curing unit was analyzed. In two commercial adhesive systems, CQ was completely replaced by Lucirin TPO. The commercial adhesives and their experimental counterparts were evaluated after curing for 10 seconds and 20 seconds with two dual-wavelength LED units and one regular LED unit, by applying the curing unit on the adhesive surface at two distances of 0 mm and 5 mm. Degree of cure and mechanical properties (Vickers hardness and modulus of elasticity) were assessed after 24-hour storage in distilled water at 37 degrees C. Experimental data showed that the CQ-amine system could be completely replaced by Lucirin TPO when dual-wavelength LED unit was used for photoactivation.

The effect of silicon doping in the selected barrier on the electroluminescence of InGaN∕GaN multiquantum well light emitting diode

The effect of silicon doping in the selected barrier on the electroluminescence of InGaN∕GaN multiquantum well light emitting diode (LED) was studied using dual wavelength LEDs. The result verified that the hole carrier transport is easily blocked by the silicon doped barrier, and the dominant electron and hole recombination occurs at the wells between p-GaN and the silicon doped barrier. The electroluminescence spectrum and the wavelength blueshift of the silicon doped LEDs were compared with undoped LEDs. The numerical simulation was done to clearly explain the hole blocking effect by the silicon doped barrier.

Advances in AlGaInN blue and ultraviolet light emitters

In this paper, we discuss the current status and the considerable challenges for extending the nitride light sources into deeper ultraviolet (UV). We also review recent progress in exploratory blue and near UV III-nitride light emitters, such as vertical cavity devices and dual-wavelength light-emitting diodes, which may provide useful device templates for applications in the deeper UV.

A dual-wavelength light-emitting diode based detector for flow-injection analysis process analysers

In this paper, a small dual-wavelength light-emitting diode (LED) based detector for FIA process analysers is designed. The detector's optical parts include a flow cell, a dual-wavelength LED and a photodiode. Neither mirrors nor lenses are used. The optical paths for the different light beams are almost the same, distinguishing it from previously reported LED based detectors. The detector's electronic components, including a signal amplifier, an A/D and D/A converter, and an Intel 8031 single-chip microcomputer, are integrated on one small board. In order to obtain response signals of approximate intensity for the two colours, the D/A converter and a multiplexer are used to adjust the emission intensity of the two colours respectively. Under microcomputer control, light beams are rapidly electronically modulated. Therefore, dark current and intensity of the light beams are measured almost simultaneously; as a result, the effect of drift is negligible. While a solution of absorbance 0.875 was measured repeatedly, an RSD (relative standard deviation) of 0.24% could be reached. Furthermore, such a detector with a red/yellow LED has been coupled with the FIA technique for the determination of 10 −6 M levels of cobalt.

Practical dual-wavelength light-emitting double diode

A practical dual-wavelength light-emitting double-diode (LEDD) device structure is presented. This device is relatively simple to fabricate and requires a single device-to-fiber alignment for packaging. Additionally, the individual wavelengths can be selected within the 0.8 to 1.6-μm low-loss spectral region of optical fibers. A dual-wavelength LEDD emitting at 1.3 and 1.1 μm is demonstrated. Powers exceeding 10 μW for each wavelength at 50-mA drive current are coupled into a lensed, graded index, 62.5-μm core, 0.29-NA optical fiber.

LEDs and photodetectors for wavelength-division-multiplexed light-wave systems

The very wide transmission window, from 0.8 to 1.6 μm wavelength, in present low-loss optical fibres offers opportunities for wavelength-division-multiplexing (WDM) in light-wave systems. This paper reviews light emitting diode (LED) light sources and photodetectors capable of meeting the power (distance) and bandwidth (bit rate) requirements of such systems. Particular attention will be paid to the new multiplexing dual wavelength LEDs and demultiplexing photodetectors which point a way toward simpler, perhaps more economical, WDM light-wave systems in wide-band loop and inter-office trunking applications.

A new InGaAsP/InP dual-wavelength LED

A new dual-wavelength light-emitting diode (LED) emitting near 1.2 and 1.3 μm has been fabricated. The differential efficiencies of the two outputs were 0.36 and 0.88%, respectively. The intensities of these optical outputs can be controlled independently. The optical cross talk between the two wavelengths was −10 and −16 dB at 1.15 and 1.35 μm, respectively. This device is useful for wavelength-multiplexed optical communication systems.

Review of some microwave integrated circuit components utilizing microstrip techniques : T. H. Oxley. Radio Electron. Engr48, (1/2) 3

In this paper, a small dual-wavelength light-emitting diode (LED) based detector for FIA process analysers is designed. The detector's optical parts include a flow cell, a dual-wavelength LED and a photodiode. Neither mirrors nor lenses are used. The optical paths for the different light beams are almost the same, distinguishing it from previously reported LED based detectors. The detector's electronic components, including a signal amplifier, an A/D and D/A converter, and an Intel 8031 single-chip microcomputer, are integrated on one small board. In order to obtain response signals of approximate intensity for the two colours, the D/A converter and a multiplexer are used to adjust the emission intensity of the two colours respectively. Under microcomputer control, light beams are rapidly electronically modulated. Therefore, dark current and intensity of the light beams are measured almost simultaneously; as a result, the effect of drift is negligible. While a solution of absorbance 0.875 was measured repeatedly, an RSD (relative standard deviation) of 0.24% could be reached. Furthermore, such a detector with a red/yellow LED has been coupled with the FIA technique for the determination of 10−6M levels of cobalt.