Blue Shift Of Electroluminescence Research Articles

Electroluminescence in Heterostructures GaSb/AlSb/InAsSb Due to Tunneling Mechanism of Radiative Recombination

We report on the unusually large blue shift of electroluminescence spectrum with increase of the drive current at 77 K in a double-barrier nanoheterostructure with a deep AlSb/InAs0.83Sb0.17/AlSb quantum well grown by MOVPE on n-GaSb:Te substrate. The rise of drive current from 20 to 220 mA led to shift of the electroluminescence spectrum maximum towards higher photon energies by 100 meV. It was shown that this effect is due to indirect (tunneling) radiative transitions between electrons in InAsSb quantum well and heavy holes localized near AlSb/p-GaSb heterointerface. Energy of radiative transition was linearly dependent on applied voltage. In the drive current range of 50–220 mA electroluminescence blue shift was accompanied by the spectrum narrowing by 40 meV and noticeable change of the spectrum shape. With rise in drive current superlinear increase of electroluminescence intensity caused by the nonlinear dependence of tunneling radiative recombination rate on transition energy was observed at 300 and 77 K.

Room-temperature photoluminescence and electroluminescence of 1.3-μm-range BGaInAs quantum wells on GaAs substrates

We report the room temperature photoluminescence and electroluminescence properties of boron incorporated into highly strained InGaAs, forming BGaInAs, grown on GaAs substrates. X-ray diffraction was used to determine the alloy composition and strain of BGaInAs quantum wells on GaAs. As expected, the addition of boron reduced the quantum well compressive strain, preventing strain-relaxation and enabling extension of the peak emission wavelength of InGaAs quantum wells to 1.3 μm on GaAs. We also report both the longest wavelength emission observed from BGaInAs (1.4 μm) and electrically injected photoemission from a dilute-boride active region. We observed a blueshift in electroluminescence, due to unintentional in situ annealing of the active region, which we mitigated to demonstrate a path to realize true 1.3 μm emitters in the presence of in situ annealing.

Large blue shift of electroluminescence spectrum in nanoheterostructures with a deep AlSb/InAsSb/AlSb quantum well

We report on the unusually large blue shift of the electroluminescence spectrum with an increase of the drive current at 77 K in a double-barrier nanoheterostructure with a deep AlSb/InAs0.83Sb0.17/AlSb quantum well grown by metal-organic vapor phase epitaxy on the n-GaSb:Te substrate. The rise of the drive current from 20 mA to 220 mA led to a shift of the electroluminescence spectrum maximum toward higher photon energies by 100 meV. It was shown that this effect is due to indirect (tunneling) radiative transitions between electrons in InAsSb quantum well and heavy holes localized near the AlSb/p-GaSb heterointerface. The energy of radiative transition was linearly dependent on the applied voltage. In the drive current range of 50–220 mA, an electroluminescence blue shift was accompanied by spectrum narrowing by 40 meV and a noticeable change of the spectrum shape. With a rise in the drive current, a superlinear increase of the electroluminescence intensity caused by the nonlinear dependence of tunneling radiative recombination rate on transition energy was observed at 300 K and 77 K.

Blue-green InGaN/GaN light-emitting diode with mesh-like top metal electrode

Light-emitting diodes (LEDs) with blue-green dual-wavelength emission and top metal electrode patterned as a mesh were fabricated using InGaN/GaN material system and tested. In pulsed voltage supply mode an increase in injected current resulted in electroluminescence (EL) with equal peak intensities of blue and green emission lines and shallow trough between them. These features of the LED EL-spectrum can be attributed to the effect of the mesh-like patterning of the top electrode.Meshed electrode promotes the injection of current spatially nonuniform along the planes of the quantum well (QWs) which results not only in spatial nonuniformity of the intensity of generated light but also may contribute to position-dependent compensation of Quantum-confined Stark effect (QCSE) resulting in blue shift of EL in the QWs. The observed phenomenon can be used to control or engineer the EL spectra of dual-wavelength LEDs by electrode patterning.

Size-controlled InGaN/GaN nanorod LEDs with an ITO/graphene transparent layer

We introduce ITO on graphene as a current-spreading layer for separated InGaN/GaN nanorod LEDs for the purpose of passivation-free and high light-extraction efficiency. Transferred graphene on InGaN/GaN nanorods effectively blocks the diffusion of ITO atoms to nanorods, facilitating the production of transparent ITO/graphene contact on parallel-nanorod LEDs, without filling the air gaps, like a bridge structure. The ITO/graphene layer sufficiently spreads current in a lateral direction, resulting in uniform and reliable light emission observed from the whole area of the top surface. Using KOH treatment, we reduce series resistance and reverse leakage current in nanorod LEDs by recovering the plasma-damaged region. We also control the size of the nanorods by varying the KOH treatment time and observe strain relaxation via blueshift in electroluminescence. As a result, bridge-structured LEDs with 8 min of KOH treatment show 15 times higher light-emitting efficiency than with 2 min of KOH treatment.

Effects of multiple interruptions with trimethylindium-treatment in the InGaN/GaN quantum well on green light emitting diodes**Project supported by the National Natural Science Foundation of China (Grant Nos. 11204360 and 61210014), the Science and Technology Planning Projects of Guangdong Province, China (Grant Nos. 2014B050505020, 2015B010114007, and 2014B090904045), the Research Fund for the Doctoral Program of Higher Education of China (Grant No.

In this study, the influence of multiple interruptions with trimethylindium (TMIn)-treatment in InGaN/GaN multiple quantum wells (MQWs) on green light-emitting diode (LED) is investigated. A comparison of conventional LEDs with the one fabricated with our method shows that the latter has better optical properties. Photoluminescence (PL) full-width at half maximum (FWHM) is reduced, light output power is much higher and the blue shift of electroluminescence (EL) dominant wavelength becomes smaller with current increasing. These improvements should be attributed to the reduced interface roughness of MQW and more uniformity of indium distribution in MQWs by the interruptions with TMIn-treatment.

Orange/yellow InGaN/AlN nanodisk light emitting diodes

AbstractIndium gallium nitride (InGaN)/aluminium nitride (AlN) self‐assembled nanodisk light emitting diode (LED) structures were grown on sapphire substrate using metalorganic vapor phase epitaxy (MOVPE). Structural analysis shows that the initial AlN layer plays a crucial role in the formation of nanodisk structure. Nanodisks were formed due to cracks introduced in the first AlN layer on n‐GaN template. The succeeding InGaN/AlN layers introduced branching of the nanodisks due to cracks from the initial AlN layer. The structural properties of nanodisk were confirmed from atomic force microscopy (AFM) and high‐angle annular dark‐field (HAADF) images. Observation of electroluminescence (EL) showed that, at lower injection current orange (605 nm) color light was emitted and that when the injection current increased the wavelength shifted from orange to yellow (586 nm). This large EL blue shift observed in the nanodisk LED was due weakening of the quantum confined stark effect (QCSE) at high injection current. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of external tensile stress on blue InGaN/GaN multi-quantum-well light-emitting diodes

The influence of external tensile stress on blue InGaN/GaN multi-quantum-well (MQW) light-emitting diodes (LEDs) is demonstrated. It was found that applying external tensile stress effectively compensates for the compressive strain developed in the InGaN active layer, thus reducing the quantum-confined Stark effect by attenuating the piezoelectric polarization from the InGaN layer. With 35A/cm2 of current density (∼50mA), the light output power could be improved by ∼40% when the LEDs were subjected to an external tensile stress. The blueshift in electroluminescence (EL) spectra was reduced by applying the external tensile stress. In contrast, when the LEDs were exposed to external compressive stress, the light output power intensity was decreased by ∼12% at a current density of 35A/cm2. The simulation results confirm that the relaxation of compressive strain in the InGaN/GaN MQW structure results in the reduction of the piezoelectric field and improves the overlap of electron and hole wave functions.

Self-Assembled InAs/GaAs Quantum Dots Covered by Different Strain Reducing Layers Exhibiting Strong Photo- and Electroluminescence in 1.3 and 1.55 <I>μ</I>m Bands

The effect of different InGaAs and GaAsSb strain reducing layers on photoluminescence and electroluminescence from self-assembled InAs/GaAs quantum dots grown by metal-organic vapour phase epitaxy was investigated. The aim was to shift their luminescence maximum towards optical communication wavelengths at 1.3 or 1.55 microm. Results show that covering by InGaAs strain reducing layer provides stronger shift of photoluminescence maximum (up to 1.55 microm) as compared to GaAsSb one with similar strain in the structure. This is caused by the increase of quantum dot size during InGaAs capping and reduction of quantum confinement of the electron wave function which spreads into the cap. Unfortunately, the weaker electron confinement in quantum dots is a reason of a considerable blue shift of electroluminescence from these InGaAs structures since optical transitions move to InGaAs quantum well. Although strong electroluminescence at 1300 nm was achieved from quantum dots covered by both types of strain reducing layers, the GaAsSb strain reducing layer is more suitable for long wavelength electroluminescence due to higher electron confinement potential allowing suppression of thermal carrier escape from quantum dots.

Green Electroluminescence From ZnCdO Multiple Quantum-Well Light-Emitting Diodes Grown by Remote-Plasma-Enhanced Metal–Organic Chemical Vapor Deposition

Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.80</sub> Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.20</sub> O/Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.92</sub> Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.08</sub> O multiple quantum-well (MQW) light-emitting diodes (LEDs) on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> -type 4H-SiC substrates, using remote-plasma-enhanced metal-organic chemical vapor deposition, have been fabricated and characterized. Band-edge green electroluminescence (EL) at 500 nm has been obtained. The ZnCdO MQW LEDs show a rectifying current-voltage behavior with a turn-on voltage of 6.0 V. The integrated EL intensity linearly increases with increasing injection current density up to 1.9 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, the presence of an EL blue-shift of 20 nm with increasing current and a large EL spectral width in comparison to PL are discussed in terms of Cd compositional fluctuations.

Blueshift of electroluminescence from single n-InP nanowire/p-Si heterojunctions due tothe Burstein–Moss effect

Single-crystalline n-type InP nanowires (NWs) with different electronconcentrations were synthesized on Si substrates via the vapor phase transportmethod. The electrical properties of the InP nanowires were investigated byfabricating and measuring single NW field-effect transistors (FETs). Single InPNW/p+-Si heterojunctions were fabricated, and electroluminescence (EL) spectra fromthem were studied. It was found that both the photoluminescence (PL) spectraof the InP NWs and the EL spectra of the heterojunctions blueshift from 920to 775 nm when the electron concentrations of the InP NWs increase from2 × 1017 to1.4 × 1019 cm−3. The blueshifts can be attributed to the Burstein–Moss effect rather than thequantum confinement effect in the InP NWs. The large blueshifts observed in thisstudy indicate a potential application of InP NWs in nano-multicolour displays.

Characteristics of long wavelength InGaN quantum well laser diodes

We demonstrated the long wavelength (485nm) lasing of InGaN laser diodes under continuous wave condition at room temperature over 10mW. Two InGaN laser structures were adapted with different indium composition for InGaN optical confinement layers (OCLs) below quantum wells. The blue shift of electroluminescence (EL) was reduced in InGaN laser diodes grown on 3% In concentration in InGaN OCL compared with 1.5% In concentration in InGaN OCL. The EL peak for laser diode with 3% In concentration in InGaN OCL occurs at longer wavelength for all current levels compared to the laser with 1.5% In concentration in InGaN OCL. In addition, the laterally nonuniform InGaN wells grown on 1.5% In concentration in InGaN OCL was verified by the cross-sectional view of InGaN active layer using high-resolution transmission electron microscopy.

Nitride-based light-emitting diodes with InGaN∕GaN SAQD active layers

InGaN/GaN blue light-emitting diodes (LEDs) with self-assembled quantum dot (SAQD) active layers were successfully fabricated using an interrupted growth method in metal- organic chemical vapour deposition (MOCVD). Nanoscale QDs have been formed successfully embedded in quantum wells (QWs) with a typical 3 nm height and 10 nm lateral dimension. A huge 68.4 meV blue shift in electroluminescence (EL) peak position was found as the injection current was increased from 3 to 50 mA for the SAQD LED. The large EL blue shift reveals that deep localisation of exitons (or carriers) originating from QDs strengthens the band-filling effect as the injection current increases.

InGaN/GaN blue light-emitting diodes with self-assembled quantum dots

InGaN/GaN blue light-emitting diodes (LEDs) with multiple quantum dot (MQD) active layers were successfully fabricated by using an interrupted growth method in metal-organic chemical vapour deposition (MOCVD). We have successfully formed nanoscale QDs embedded in quantum wells with a typical 3 nm height and 10 nm lateral dimension. It was found that a huge 68.4 meV blue shift in electroluminescence (EL) peak position as the injection current is increased from 3 to 50 mA for the MQD LED. The large EL blue shift reveals that deep localization of exitons (or carriers) originates from QDs will strengthen the band-filling effect as the injection current increases.

Electroluminescent Properties of a Bis(2-methyl-8-quinolinato) Aluminum Hydroxide Complex

Organic electroluminescence (EL) devices were fabricated using a bis(2-methyl-8-quinolinato) aluminum hydroxide complex [Al(Mq)2OH] as the light-emitting material. The device exhibits bright blue EL at a peak wavelength of 485 nm. A maximum luminance of about 14,000 cd/m2 can be achieved at a driving current density of 480 mA/cm2. The efficiency of the device is about 4.6 cd/A. Possible mechanisms of EL blue shift of Al(Mq)2OH with respect to Alq3 are discussed.

Frequency response of molecularly thin alternating current light-emitting diodes

The frequency response of molecularly thin alternating-current polymeric light-emitting diodes has been studied. Langmuir–Blodgett (LB) films of poly(3-hexylthiophene) (PHT) were used as the active emitting material and the device was formed by sandwiching PHT films between LB films of emeraldine base polyaniline. As a step towards molecular electronic devices, we have shown that even two molecular layers of PHT (≈6 nm) are sufficient for light emission. The high frequency operation limit of the device has been discussed in terms of a charge accumulation process at the polymer–polymer interface. The electroluminescence (EL) spectra of different structures have been compared with corresponding photoluminescence spectra. A significant blueshift in EL has been observed in thinner structures and its origin has been discussed.