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A study of submicron‐sized InGaN containing a single quantum well, intended for use as nano‐light‐emitting diodes in high‐resolution display based on direct emission, is presented. Herein, the structures are grown by a bottom‐up method from holes in a masked GaN/sapphire substrate and are intended for red emission. Many of the platelets show dark lines in cathodoluminescence images, previously identified as stacking mismatch boundaries. These introduce local shifts in the reduced emission, perhaps related to local strain. However, the total emission position stays unaffected, just reduced in intensity. Due to an unintended variation in the size of the c‐facet, there is a gradient in the indium content which, in turn, leads to a significant shift in the peak position of the quantum well emission. With increasing probe current there is a slight blueshift, likely a result of the quantum confined Stark effect. [ABSTRACT FROM AUTHOR]

This article presents the effect of aluminium nitride (AlN) epilayer (EPL) growth rate on the growth of semipolar (11–22) InGaN/GaN light emitting diode (LED). Three samples are grown with different AlN EPL growth rates, which are low (L1, 1.0 nm s−1), intermediate (L2, 1.3 nm s−1), and high (L3, 1.6 nm s−1) growth rate. The root‐mean‐square (RMS) and peak‐to‐valley roughness show an increasing trend with the increasing AlN EPL growth rate which is attributed to an increment in indium composition as justified by the photoluminescence results. The sample with AlN EPL growth rate of 1.3 nm s−1 (L2) exhibits an outstanding crystal quality in terms of defect densities reduction, with a minimum basal stacking fault density of 1.60 × 104 cm−1 as calculated. Besides that, the obvious fringes of InGaN/GaN peaks observed in 2θ−ω scan proves that a high abruptness multi‐quantum well is attained. Sample L2 also shows a single peak profile in both photoluminescence and electroluminescence spectra with green wavelength emission of 506 and 537 nm, respectively, indicating a homogeneous indium composition. As the injection current is swept from 5 to 40 mA for sample L2, a weak blueshift of ≈6 nm is observed which indicates a reduction in quantum‐confined Stark effect (QCSE). [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are widely used as next-generation light sources because of their various advantages. However, their luminous efficiency is remarkably low at the green-emission wavelength. The luminous efficiencies of InGaN/GaN quantum wells (QWs) significantly decrease with increasing indium content in the green wavelength region, mainly owing to the quantum-confined Stark effect (QCSE). This green gap problem can be solved using QWs grown on semi-polar GaN substrates, such as the {11–22} planes, to reduce the QCSE. We propose that the use of surface plasmons (SPs) is a promising way to improve the light emission efficiency of light-emitting materials such as InGaN/GaN QWs. SP resonance increases the spontaneous emission rates of the excited states, causes a relative reduction in non-radiative relaxation, and ultimately increases the internal quantum efficiencies. In this study, the light emissions of InGaN/GaN QWs grown on polar and semi-polar GaN were investigated using micro-photoluminescence (PL). We successfully enhanced the light emission of semi-polar GaN via SP resonance. The PL peak intensities and wavelengths were mapped and compared to determine the underlying mechanisms. We also measured the emission lifetimes by time-resolved PL and interpreted the detailed mechanism of SP-enhanced emissions. It was found that SP resonances can control not only the emission efficiency but also the exciton dynamics, such as exciton localization effects, QCSE screening, and defect level saturation. We conclude that the green gap problem can be solved by SP-enhanced light emission in semipolar InGaN/GaN. [ABSTRACT FROM AUTHOR]

Semi-polar orientation owns the advantage of reduced internal piezoelectric fields by tilting the growth direction away from the conventional c -direction. The crystal symmetry and the balanced biaxial stress in growth plane are inevitably broken in the semi-polar orientation, leading to the appearance of anisotropic properties in both structural and optical performance. This report has investigated the structural and optical properties of semi-polar (20–21) InGaN/GaN multiple quantum wells overgrown on patterned sapphire substrates with a wide wavelength range from 415 nm to 521 nm. Polarization switching was not observed on these semi-polar (20–21) samples. The polarization ratio monotonically increases from 0.18 to 0.43 with increasing the emission wavelength, and the energy difference simultaneously increases from 17 meV to 29 meV. As increasing the excitation laser power, the polarization ratio drops slightly while the energy difference remains stable, indicating a saturation of the recombination to the topmost valence subband. These results help exploit the anisotropic structural and optical properties of semi-polar nitrides and promote the development of highly polarized light source for the application in the fields of display and communication. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Computer vision techniques are real-time, immersive, and perceptual human-computer interaction technology. Excellent display effect, dynamic surface flexibility, and safe bio-adhesion are essential for various human–computer interaction applications, such as metaverse interfaces, skin-like sensors, and optoelectronic medical devices. However, realizing the flexible matching of inorganic optoelectronic devices and organisms remains a grand challenge for current display technologies. Here, we proposed a novel strategy by combining the optoelectronic advantages of inorganic micro light emitting diode (micro-LED) display and the extraordinary mechanical/biological compatibility of organic materials to overcome this challenge. A highly elastic (greater than 2000% strain), highly transparent (94% visible light transmittance), biocompatible conductive hydrogel composite electrode layer was fabricated. For the first time, we realized the on-chip electrical interconnection of 4900 LED units to form a blue-green light display patch with high resolution (264 PPI), low power consumption (4.4 mW) and adaptive surface attachment. This work demonstrates an integrated scheme and potential applications of flexible high-resolution microdisplays, such as wearable full-color micro-LED smart curved display devices and conformable biomedical monitoring systems. [ABSTRACT FROM AUTHOR]

The analysis of the photoluminescence of polar light emitting diode (LED) structures with a 25 nm In0.17Ga0.83N quantum well is reported. The observed emission most likely originates from a set of energetically close excited states (ES), while the ground state decays only extremely slowly on a μs‐to‐ms timescale, that is, long‐living charge accumulates there. However, this population can also be quantified spectroscopically by applying short reverse voltage pulses. The emission from ES is effective and nearly exponential with decay time constants of 1.5 and 8 ns at 6 and 300 K, respectively, and is likely dominated by radiative processes. These findings point to a possible route to improved polar device architectures. [ABSTRACT FROM AUTHOR]

A decrease in external quantum efficiency (EQE) of commercial LEDs based on MQW InGaN/GaN at wavelengths of 445, 530 and MQW AlGaN/GaN at 280 nm was experimentally studied in the standard aging mode at direct current. The decrease in EQE (regardless of the radiation wavelength) is found out to occur due to cooperative phenomena developing in 1–2 quantum wells (QWs) located in the space charge region (SCR) around the p–n junction, as well as in most of the QWs outside of SCR. It is shown that the inhomogeneous flow of current in these regions leads not only to the transformation of defects localized at heteroboundaries in the SCR and in lateral inhomogeneities in the alloy composition outside of SCR as well as in the extended defects, but also to a change in the alloy composition. [ABSTRACT FROM AUTHOR]

Research on enhancement green light emitter is important to obtain a perfect red-green-blue (RGB) induced white light source. Unfortunately the present of mixed phase in deposition of InGaN/GaN limited the potential LED efficiency. Therefore, we introduce a new method called as Low Temperature Ammonia Treatment (LTAT) to eliminate the mixed phase and to enhance the structure properties of InGaN/GaN. Two samples have been prepared, with LTAT (LED A) and without LTAT (LED B). Both samples have been characterized using optical microscope (OM), Atomic Force Microscope (AFM), X-ray rocking curve (XRC) and Electroluminescence (EL). On the structural characterization, the OM results show the present 3D island on LED B sample while sample LED A only shows 2D surface. The RMS surface roughness from AFM are 10.3 ± 0.4 nm and 13.5 ± 10.7 nm for LED A and LED B respectively. XRC analysis proved the LED A with LTAT has a homogenous XRD curve while LED B without LTAT has a mixed phase. The BSFs streak length measured as 1.42 nm−1 and 1.61 nm−1 for LED A and LED B respectively shows low crystallographic defect in LED A compared to LED B. For the EL characteristic, LED A shows a single sharp peak near 538.2 nm wavelength, while LED B shows a broad multi-peak profile at 435.7 nm, 480.6 nm and 520.5 nm. The single sharp peak shows enhancement in green light emission when LTAT is applied during deposition. Successful enhancement is structural and electroluminescence properties shows the effectiveness of LTAT proposed in this work for perfect RGB. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Models describing the tunneling of electrons and holes through parabolic InxGa1−xN/GaN quantum well/LED structures with respect to strain were developed. The transmission coefficient, tunneling lifetime, and efficiency of LED structures were evaluated by solving the Schrödinger equation. The effects of the mole fraction on the structure strain, resonant tunneling and tunneling lifetime, and LH–HH splitting were characterized. The value of LH–HH splitting increased and remained higher than the Fermi energy; therefore, only the HH band was dominant in terms of the valence band properties. The results indicate that an increase in the mole fraction can lead to efficiency droop. [ABSTRACT FROM AUTHOR]

Simulations on mobility influence in optoelectronics parameters from an InGaN/GaN blue LED using the Nextnano++ software arepresented in this paper. These simulations were performed by changing the hole and electron mobility value for the material compounds according to experimental, theoretical, and doping-concentration data already reported in the literature. The power law mobility is used for the current calculation in the quantum drift-diffusion model. The results indicate the lower hole and electron leakage currents correspond to the lowest mobility values for the InGaN alloy, the greatest amount of recombination occurs in the extreme wells within the active layer of the LED and the stable emission is at 3.6 V with peak wavelength λ ^ L E D = 456.7   nm and full width at half maximum F W H M ~ 11.1   nm for the three mobilities. Although experimental and theoretical mobility values reach higher carrier density and recombination, the photon emission is broader and unstable. Additionally, the doping-concentration mobility results in lower wavelength shifts and narrows FWHM, making it more stable. The highest quantum efficiency achieved by doping-concentration mobility is only in the breakdown voltage ( η d o p − m a x = 60.43 % ), which is the IQE value comparable to similar LEDs and is more useful for these kinds of semiconductor devices. [ABSTRACT FROM AUTHOR]

Visualization is a direct, efficient, and simple interface method to realize the interaction between human and machine, whereas the flexible display unit, as the major bottleneck, still deeply hinders the advances of wearable and virtual reality devices. To obtain flexible optoelectronic devices, one of the effective methods is to transfer a high-efficient and long-lifetime inorganic optoelectronic film from its rigid epitaxial substrate to a foreign flexible/soft substrate. Additionally, piezo-phototronic effect is a fundamental theory for guiding the design of flexible optoelectronic devices. Herein, we demonstrate a flexible, stretchable, and transparent InGaN/GaN multiple quantum wells (MQWs)/polyacrylamide (PAAM) hydrogel-based light emitting diode coupling with the piezo-phototronic effect. The quantum well energy band and integrated luminous intensity (increased by more than 31.3%) are significantly modulated by external mechanical stimuli in the device. Benefiting from the small Young's modulus of hydrogel and weak Van der Waals force, the composite film can endure an extreme tensile condition of about 21.1% stretching with negligible tensile strains transmitted to the InGaN/GaN MQWs. And the stable photoluminescence characteristics can be observed. Moreover, the hydrogen-bond adsorption and excellent transparency of the hydrogel substrate greatly facilitate the packaging and luminescence of the optoelectronic device. And thus, such a novel integration scheme of inorganic semiconductor materials and organic hydrogel materials would help to guide the robust stretchable optoelectronic devices, and show great potential in emerging wearable devices and virtual reality applications. [ABSTRACT FROM AUTHOR]

The family of III-nitride materials has provided a platform for tremendous advances in efficient solid-state lighting sources such as light-emitting diodes and laser diodes. In particular, quantum dot (QD) lasers using the InGaN/GaN material system promise numerous benefits to enhance photonic performance in the blue wavelength regime. Nevertheless, issues of strained growth and difficulties in producing InGaN QDs with uniform composition and size pose daunting challenges in achieving an efficient blue laser. Through a review of two previous studies on InGaN/GaN QD microdisk lasers, we seek to provide a different perspective and approach in better understanding the potential of QD emitters. The lasers studied in this paper contain gain material where QDs are sparsely distributed, comprise a wide distribution of sizes, and are intermixed with “fragmented” quantum well (fQW) material. Despite these circumstances, the use of microdisk cavities, where a few distinct, high-quality modes overlap the gain region, not only produces ultralow lasing thresholds (∼6.2 μJ/cm2) but also allows us to analyze the dynamic competition between QDs and fQWs in determining the final lasing wavelength. These insights can facilitate “modal” optimization of QD lasing and ultimately help to broaden the use of III-nitride QDs in devices.

Ultra-dense (>4,000 pixels per inch) and highly stable full-color III-nitride nanoscale pixels are crucial for near-eye display technologies like virtual and augmented-reality glasses. In this context, InGaN-based long wavelength green microscale light-emitting diodes face major bottlenecks, such as low efficiency and inadequate wavelength stability. These challenges are associated with the presence of both nonradiative surface defects and the strain induced quantum-confined Stark effect. Herein, we report nanoscale pixelation of green InGaN/GaN LEDs incorporating strain-engineered ultra-dense nanowire (NW) arrays, corresponding to ∼36,000 pixels per inch. The NW pixel arrays exhibit a stable peak wavelength emission at ∼500 nm for over 3 orders of magnitude of injection current densities (from ∼4 A/cm 2 to ∼1 kA/cm 2 ). The observed wavelength stability enhancement (a reduced blue-shift of just ∼4 nm) directly results from the suppressed built-in electric field achieved by strain relaxation of the axial multi quantum wells in the NWs. Finite difference time domain simulations show that emission of the pixel array is significantly increased owing to the enhanced spontaneous emission rate (characterized by a high Purcell factor of ≈2) of the ultra-dense NWs. We have demonstrated top-down NWs, where each NW (diameter ranging down to 200 nm) shows excellent uniformity and light output characteristics in direct contrast to bottom-up grown NW heterostructures. The results of this study establish a viable route for realizing nanoscale pixels with high luminescence stability and wafer-scale uniformity with high (>20%) indium composition InGaN/GaN LED heterostructures, for next-generation near-eye displays.

This paper presents the results of a numerical analysis of nitride-based edge-emitting lasers with an InGaN/GaN active region designed for continuous wave room temperature emission of green and blue light. The main goal was to investigate whether the indium thin oxide (ITO) layer can serve as an effective optical confinement improving operation of these devices. Simulations were performed with the aid of a self-consistent thermal-electrical-optical model. Results obtained for green- and blue-emitting lasers were compared. The ITO layer in the p-type cladding was found to effectively help confine the laser mode in the active regions of the devices and to decrease the threshold current density.

Semi-polar micro-LEDs have gain increasing interests due to the advantages of polarization control and quantum efficiency improvement. In this work, a novel semi-polar (20-21)-plane micro-LEDs array has been designed and manufactured. In comparison with c-plane micro-LEDs, semi-polar micro-LEDs indicate better electrical and optical performance. The relative EQE of semi-polar micro-LEDs remains at 62% under the injected current density of 775.6 A/cm2, which indicates a reduced efficiency droop due to less polarization in MQWs. It has been further proved by a significant reduction of 55% in emission peak blue-shift under the injected current density from 11.1 A/cm2 to 775.6 A/cm2. In addition, the carrier recombination dynamics and spatial light distribution of semi-polar micro-LEDs with different pixel sizes have been studied. Fast recombination lifetime in smaller size semi-polar micro-LEDs indicates a promising way to be used as a high modulation bandwidth light source. Stable and uniform light distribution in a wider range of spatial azimuths further supports for the semi-polar micro-LEDs as a strong candidate for the applications of high-resolution display and high-speed visible light communication.

Research on enhancement green light emitter is important to obtain a perfect red-green-blue (RGB) induced white light source. Unfortunately the present of mixed phase in deposition of InGaN/GaN limited the potential LED efficiency. Therefore, we introduce a new method called as Low Temperature Ammonia Treatment (LTAT) to eliminate the mixed phase and to enhance the structure properties of InGaN/GaN. Two samples have been prepared, with LTAT (LED A) and without LTAT (LED B). Both samples have been characterized using optical microscope (OM), Atomic Force Microscope (AFM), X-ray rocking curve (XRC) and Electroluminescence (EL). On the structural characterization, the OM results show the present 3D island on LED B sample while sample LED A only shows 2D surface. The RMS surface roughness from AFM are 10.3 ± 0.4 nm and 13.5 ± 10.7 nm for LED A and LED B respectively. XRC analysis proved the LED A with LTAT has a homogenous XRD curve while LED B without LTAT has a mixed phase. The BSFs streak length measured as 1.42 nm−1 and 1.61 nm−1 for LED A and LED B respectively shows low crystallographic defect in LED A compared to LED B. For the EL characteristic, LED A shows a single sharp peak near 538.2 nm wavelength, while LED B shows a broad multi-peak profile at 435.7 nm, 480.6 nm and 520.5 nm. The single sharp peak shows enhancement in green light emission when LTAT is applied during deposition. Successful enhancement is structural and electroluminescence properties shows the effectiveness of LTAT proposed in this work for perfect RGB.

Models describing the tunneling of electrons and holes through parabolic InxGa1−xN/GaN quantum well/LED structures with respect to strain were developed. The transmission coefficient, tunneling lifetime, and efficiency of LED structures were evaluated by solving the Schrödinger equation. The effects of the mole fraction on the structure strain, resonant tunneling and tunneling lifetime, and LH–HH splitting were characterized. The value of LH–HH splitting increased and remained higher than the Fermi energy; therefore, only the HH band was dominant in terms of the valence band properties. The results indicate that an increase in the mole fraction can lead to efficiency droop.

Simulations on mobility influence in optoelectronics parameters from an InGaN/GaN blue LED using the Nextnano++ software arepresented in this paper. These simulations were performed by changing the hole and electron mobility value for the material compounds according to experimental, theoretical, and doping-concentration data already reported in the literature. The power law mobility is used for the current calculation in the quantum drift-diffusion model. The results indicate the lower hole and electron leakage currents correspond to the lowest mobility values for the InGaN alloy, the greatest amount of recombination occurs in the extreme wells within the active layer of the LED and the stable emission is at 3.6 V with peak wavelength λ^LED=456.7 nm and full width at half maximum FWHM~11.1 nm for the three mobilities. Although experimental and theoretical mobility values reach higher carrier density and recombination, the photon emission is broader and unstable. Additionally, the doping-concentration mobility results in lower wavelength shifts and narrows FWHM, making it more stable. The highest quantum efficiency achieved by doping-concentration mobility is only in the breakdown voltage (ηdop−max=60.43%), which is the IQE value comparable to similar LEDs and is more useful for these kinds of semiconductor devices.

Micro/nanowire light‐emitting diodes (LEDs) have inspired considerable research interests due to their potential applications in microdisplays and micro/nano‐optoelectronic integrated systems. Herein, a single InGaN/GaN multiple‐quantum‐well (MQW) microwire‐based flexible LED with high‐efficiency current injection and spreading is fabricated, and the performance modulation of the device by external strain is further studied. The results show that under external compressive strains, the output power is enhanced and the peak wavelength is blue shifted; on the contrary, the output power declines and the peak wavelength is red shifted under stretch strains. Compared with strain‐free devices, the flexible LED achieves the best performance at a − 1% compressive strain, with external quantum efficiency (EQE) increasing by 14.2% and efficiency droop reducing by 17.9%. The effective improvements are attributed to external strain‐induced piezoelectric polarization charges presented at local junctions/interfaces tuning the energy band. Herein, an efficient external modulation of light emission properties in a single InGaN/GaN MQW microwire LED is presented. [ABSTRACT FROM AUTHOR]

As the most promising optoelectronic device in the 21st century, the research of epitaxial structure of light-emitting diode has been a hot topic for scientists. Three types of InGaN/GaN micro-array with different morphologies were grown on graphical sapphire substrate by selective regional epitaxy using metal organic chemical vapor deposition technology. The size of the array is 6 μm. The tablets array is dominated by (0001)c facet, the height is 0. 6 μm; the platelets array includes one (0001)c facet and six equivalent (10-11) semi-polar facets, the height is 1. 2 μm; the pyramid-like array is dominated by (10-11) semi-polar facet and the height is 5 μm. The luminescence properties of InGaN/GaN micro-array structure were characterized by micro-area photoluminescence spectrometer and the results show that InGaN/GaN micro-array with different morphologies could achieve multi-wavelength emission, but its luminescence properties are heavily dependent on the morphology. Cathodic fluorescence spectra results show that the InGaN/GaN platelets array's wavelength covering red, green and blue was obviously different for different test positions, which is mainly attributed to surface migration effect and transverse gas phase diffusion resulting in nonuniform distribution of In content in each position. Moreover, the results of energy dispersive spectrometer analysis show that the In content on different facets are different, and the (0001)c facet content is more than that of (10-11) semi-polar facets. For the realization of multi-emission and new optoelectronic device design, the successful preparation InGaN/GaN micro-array is very significance. [ABSTRACT FROM AUTHOR]

The methodology of statistical analysis of cathodoluminescence (CL) intensity mappings on ensembles of several hundreds of InGaN/GaN nanowires (NWs) used to quantify non-radiative recombination centres (NRCs) was validated on InGaN/GaN NWs exhibiting spatially homogeneous cathodoluminescence at the scale of single NWs. Cathodoluminescence intensity variations obeying Poisson's statistics were assigned to the presence of randomly incorporated point defects acting as NRCs. Additionally, another type of NRCs, namely extended defects leading to spatially inhomogeneous cathodoluminescence intensity at the scale of single InGaN/GaN NWs are revealed by high resolution scanning transmission electron microscopy, geometrical phase analysis and two-beam diffraction conditions techniques. Such defects are responsible for deviations from Poisson's statistics, allowing one to achieve a rapid evaluation of the crystallographic and optical properties of several hundreds of NWs in a single cathodoluminescence intensity mapping experiment., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

The efficiency droop characteristics of single quantum well (SQW) InGaN/GaN light-emitting diodes (LEDs) including the phase-space filling (PSF) effect are predicted by a three-dimensional (3-D) numerical simulation. The carrier transport is based on the solution of the 3-D non-linear Poisson and drift-diffusion equations for both holes and electrons. A modified formulation of the Shockley-Reed-Hall (SRH) coefficient is proposed to describe the SRH carrier lifetime behavior, which increases at a low excitation level and decreases at a higher one. The current crowding causes a non-uniform distribution of the carrier concentration in the active layer that leads to the inversion of the local internal quantum efficiency (IQE) under the n-pad region when the injection current density increases from low to high levels. To further understand the correlation of the efficiency droop with the PSF effect, we systematically investigate carrier transport in the SQW InGaN/GaN LEDs and how the different PSF effect coefficients affect the current-voltage curve and IQE. The lumped IQE found in this study agrees well with previous experimental measurements. Moreover, the PSF effect has a strong impact on the IQE behavior including its peak and droop in efficiency.

The family of III-nitride materials has provided a platform for tremendous advances in efficient solid-state lighting sources such as light-emitting diodes and laser diodes. In particular, quantum dot (QD) lasers using the InGaN/GaN material system promise numerous benefits to enhance photonic performance in the blue wavelength regime. Nevertheless, issues of strained growth and difficulties in producing InGaN QDs with uniform composition and size pose daunting challenges in achieving an efficient blue laser. Through a review of two previous studies on InGaN/GaN QD microdisk lasers, we seek to provide a different perspective and approach in better understanding the potential of QD emitters. The lasers studied in this paper contain gain material where QDs are sparsely distributed, comprise a wide distribution of sizes, and are intermixed with "fragmented" quantum well (fQW) material. Despite these circumstances, the use of microdisk cavities, where a few distinct, high-quality modes overlap the gain region, not only produces ultralow lasing thresholds (∼6.2 μJ/cm2) but also allows us to analyze the dynamic competition between QDs and fQWs in determining the final lasing wavelength. These insights can facilitate "modal" optimization of QD lasing and ultimately help to broaden the use of III-nitride QDs in devices. [ABSTRACT FROM AUTHOR]

Hybrid solar electricity generation combines the high efficiency of photovoltaics (PVs) with the dispatchability of solar thermal power plants. Recent thermodynamic analyses have shown that the most efficient strategy constitutes an integrated concentrating PV‐thermal absorber operating at high solar concentration and at the high temperatures suitable to efficient commercial steam turbines (~673–873 K). The recuperation of PV thermalization losses and the exploitation of sub‐bandgap photons can more than compensate for the inherent decrease of PV efficiency with temperature in properly tailored tandem solar cells for which promising candidates are III–N alloys. Recently, there have been considerable efforts to develop apposite InGaN solar cells by producing InGaN/GaN multiple quantum wells (MQWs) as the top cell in a tandem PV device that would absorb the short‐wavelength regime of the solar spectrum, while sub‐bandgap photons and PV thermalization are absorbed in the thermal receiver. We present measurements of current–voltage curves and external quantum efficiency spectra for InGaN/GaN MQW solar cells under high sunlight intensity, up to 1 W/mm2 (1000 suns) and elevated temperature, up to 723 K. We find that the short‐circuit current increases significantly with temperature, while the magnitude of the temperature coefficient of the open‐circuit voltage decreases with solar concentration according to basic photodiode theory. Conversion efficiency peaks at 623–723 K under ~300 suns, with no perceptible worsening in cell performance under extensive temperature and irradiance cycling—an encouraging finding in the quest for high‐temperature high‐irradiance cells. [ABSTRACT FROM AUTHOR]

The emission uniformity of LED chips in the entire range of brightness and colors is the problem in LED displays manufacture process. It was approved that at lowering brightness gradations appearing the radiation nonuniformity between LED chips, and the higher disorders will be seen on the lesser emission levels. The RGB LED chips, observed by us, were based on AlGaInP (red), In0.3Ga0.7N/GaN (green), and In0,2Ga0,8NN/ GaN (blue) and had nominal working current 20 mA. Analysis of the current-voltage characteristics and capacitance-voltage characteristics showed the presence of inhomogeneous semiconductor junctions and ohmic contacts in blue LEDs structures that are the source of possible irregularities in the final emission of LED displays. The variation of voltages (at current 10 mA) were 2.81—2.98 V for blue structures, and 1.9—2.0 V for red ones. Some of the blue structures had additional parasite current-flow mechanism at low current. Rise time and fall time of electroluminescence pulse of blue structures were measured. The shortest LED pulse time in LED displays is limited by duration of 6—8 ns. The quality of LED displays may be improved by implementating the preliminary control of LED chips in a narrower range of voltage variation at operating currents, or more narrow interval of I—V variation. This additional LEDs sorting will of course reduce the percentage of the total amount of light-emitting diodes, but may improve the image (video, photo) quality at translations by using a lower brightness gradations.

In this work, we demonstrate efficient light down-conversion via FRET in InGaN/GaN multiple quantum well (MQW) nanohole arrays, coated with green-emitting CsPbBr3 and FAPbBr3 nanocrystals (NCs) and near-infrared (IR) FAPbI3 NC overlayers for solid-state lighting. Patterning the InGaN MQW into nanohole arrays allows a minimum nitride–NC separation while increasing the heterointerfacial area, thus improving simultaneously the nonradiative and radiative transfer efficiencies. Detailed spectroscopic studies of steady-state and time-resolved photoluminescence indicate a significant reduction in the quantum well photoluminescent decay time in the presence of NCs, accompanied by a significant concurrent increase of the NC integrated emission, providing evidence of efficient light down-conversion mediated by FRET with efficiencies as high as ∼83 ± 6% in the green and ∼74 ± 5% in the near-IR. [ABSTRACT FROM AUTHOR]

Semi-polar micro-LEDs have gain increasing interests due to the advantages of polarization control and quantum efficiency improvement. In this work, a novel semi-polar (20–21)-plane micro-LEDs array has been designed and manufactured. In comparison with c-plane micro-LEDs, semi-polar micro-LEDs indicate better electrical and optical performance. The relative EQE of semi-polar micro-LEDs remains at 62% under the injected current density of 775.6 A/cm2, which indicates a reduced efficiency droop due to less polarization in MQWs. It has been further proved by a significant reduction of 55% in emission peak blue-shift under the injected current density from 11.1 A/cm2 to 775.6 A/cm2. In addition, the carrier recombination dynamics and spatial light distribution of semi-polar micro-LEDs with different pixel sizes have been studied. Fast recombination lifetime in smaller size semi-polar micro-LEDs indicates a promising way to be used as a high modulation bandwidth light source. Stable and uniform light distribution in a wider range of spatial azimuths further supports for the semi-polar micro-LEDs as a strong candidate for the applications of high-resolution display and high-speed visible light communication. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical analysis of nitride-based edge-emitting lasers with an InGaN/GaN active region designed for continuous wave room temperature emission of green and blue light. The main goal was to investigate whether the indium thin oxide (ITO) layer can serve as an effective optical confinement improving operation of these devices. Simulations were performed with the aid of a self-consistent thermal-electrical-optical model. Results obtained for green- and blue-emitting lasers were compared. The ITO layer in the p-type cladding was found to effectively help confine the laser mode in the active regions of the devices and to decrease the threshold current density. [ABSTRACT FROM AUTHOR]

The performance of InGaN/GaN multiple quantum well (MQW) solar cells with five different Si-doping concentrations, namely 0, 4 × 1017 cm–3, 1 × 1018 cm–3, 3 × 1018 cm–3 and 6 × 1018 cm–3, in GaN barriers is investigated. Increasing Si-doping concentration leads to better transport property, resulting in smaller series resistance (Rs). However, the crystal quality degrades when Si-doping concentration is over 1 × 1018 cm–3, which reduces the external quantum efficiency, short circuit current density and open circuit voltage. As a result, the sample with a slight Si-doping concentration of 4 × 1017 cm–3 exhibits the highest conversion efficiency. [ABSTRACT FROM AUTHOR]

Gallium-nitride-based SLEDs are attractive light sources for augmented reality displays and other applications. However, the electrical-to-optical power conversion efficiency (PCE) of SLEDs is still far below the record-high values reported for LEDs. Utilizing advanced numerical device simulation, this paper investigates the internal physical processes that cause the low PCE of SLEDs. The poor hole conductivity strongly reduces the electrical efficiency, similar to laser diodes. However, in contrast to laser diodes, the rising carrier density in the active layers is identified as main reason for enhanced Auger recombination that severely limits the internal quantum efficiency. Design improvement options are demonstrated. [ABSTRACT FROM AUTHOR]

We demonstrate a hybrid structure incorporating concave-convex circular composite textured sidewalls and snowflake-like p-electrode, which is an effective approach to improve optical properties without deteriorating the electrical characteristics for micro-LEDs. Compared to the device with flat sidewalls and disk p-electrode, the device with concave-convex circular composite textured sidewalls and 6-branches snowflake-like p-electrode exhibits a saturation light output power enhancement of 36.85%. And the forward voltage decreases by 7.6% at current density of 1732.4 A/cm2. The enhanced performances are mainly attributed to the decrease of total internal reflection at the concave-convex circular composite textured sidewalls and improvement of current distribution provided by 6-branches snowflake-like p-electrode. [ABSTRACT FROM AUTHOR]

We demonstrate that the concave-convex circular composite structure sidewall prepared by inductively coupled plasma (ICP) etching is an effective approach to increase the light efficiency without deteriorating the electrical characteristics for micro light-emitting diodes (LEDs). The saturated light output power of the device using the concave-convex circular composite structure sidewalls with a radius of 2 μm is 39.75 mW, an improvement of 7.2% compared with that of the device using flat sidewalls. The enhanced light output characteristics are primarily attributed to the increased photon emitting due by decreasing the total internal reflection without losing the active region area. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical analysis of nitride-based edge-emitting lasers with an InGaN/GaN active region designed for continuous wave room temperature emission of green and blue light. The main goal was to investigate whether the indium thin oxide (ITO) layer can serve as an effective optical confinement improving operation of these devices. Simulations were performed with the aid of a self-consistent thermal-electrical-optical model. Results obtained for green- and blue-emitting lasers were compared. The ITO layer in the p-type cladding was found to effectively help confine the laser mode in the active regions of the devices and to decrease the threshold current density. [ABSTRACT FROM AUTHOR]

Micro/nanowire light-emitting diodes have inspired considerable research interests due to their wide range of potential applications, such as in micro/nanoscale display, optical communication and optical logics. To realize a single wire light-emitting diode, however, it is usually faced with low-efficiency or wavelength uncontrollable. Herein, we report on an individual coaxial core/shell InGaN/GaN microwire light-emitting diode with tunable dual-/single-wavelength light emission, which can be feasibly realized by controlling growth rate of microwires using MOCVD. The unique cross-sectional morphologies of synthesized microwires can simplify the device fabrication process and are in favor of vertical current injection and spreading simultaneously. Thus, the microwire light-emitting diodes show advantages at the suppression of efficiency droop under large current injection, with a drop ratio of 19.6%, as increasing the injection current from 2.4 A cm−2 to 92.6 A cm−2. This study proposes a core/shell multiple quantum wells microwire structure to fabricate micro light-emitting diodes which may act as a reliable light source for micro/nanoscale integrated photonic systems. Image 1 • Core-shell InGaN/GaN MQWs microwire were synthesized on patterned Si substrate. • The growth rate ratio between polar and semipoar MQWs was about 6.4. • The In content ratio between polar and semipoar MQWs was about 1.64. • Dual/single-wavelength microwire LEDs were fabricated and analyzed. • The microwire LEDs showed small efficiency droop at large injection current. [ABSTRACT FROM AUTHOR]

Abstract Radiation effects of 10 MeV electrons on blue-lighting InGaN/GaN multiple quantum wells (MQWs) and ultraviolet-lighting GaN/AlGaN MQWs were investigated and compared by means of temperature-dependent and time-resolved photoluminescence (PL) methods. It was found that GaN/AlGaN MQWs showed better radiation tolerance than InGaN/GaN MQWs. In detail, the internal quantum efficiency of InGaN/GaN MQWs decreased sharply with increasing electron irradiation fluence whereas that of GaN/AlGaN MQWs remained nearly constant. The degradation of the emission properties of InGaN/GaN MQWs after irradiation was attributed to the generation of non-radiation recombination centers (NRCs) in MQWs. On the other hand, the radiation hardness of GaN/AlGaN MQWs was proved to be related to two factors: the irradiation-induced reduction of both exciton localization energy and NRC density. The results reported here are significant for the evaluation and design of GaN-based optoelectronic and electronic devices used in radiation environments. [ABSTRACT FROM AUTHOR]

The physical effects of the polarization-induced charge density on the losses due to Shockley–Read–Hall (SRH) recombination in InGaN/GaN solar cells under conditions of low p-GaN doping density (~ 5 × 1017 cm−3) are discussed. Theoretical studies are performed for four p-i-n InxGa1−xN/GaN heterostructures (with x = 0.10, 0.15, 0.20, and 0.25) to analyze the effect of the polarization-induced interface charges on the built-in field present across the absorption region of the cell, which is otherwise responsible for the extraction of photogenerated charge carriers. Furthermore, the role of polarization matching layers, strategically placed at the i-InGaN/p-GaN interface, in countering the SRH recombination-induced dark current density is discussed based on simulations performed using APSYS software from Crosslight. The simulation results are validated using a mathematical model. [ABSTRACT FROM AUTHOR]

The investigation of the III-V nitride-based driving circuits is in demand for the development of GaN-based power electronic devices. In this work, we aim to grow high-quality InGaN/GaN heterojunctions on the n-channel AlGaN/GaN-on-Si high electron mobility transistor (HEMT) templates to pursue the complementary p-channel conductivity to realize the monolithic integrated circuits. As the initial step, the epitaxial growth is optimized and the structure properties are investigated by comparing with the InGaN/GaN heterojunctions grown on GaN/sapphire templates. It is found that both the In composition and relaxation degree are higher for the InGaN/GaN on the HEMT template than that on the sapphire substrate. The crystalline quality is deteriorated for the InGaN grown on the HEMT template, which is attributed to the poor-quality GaN channel in the HEMT template. Further analysis indicates that the higher In incorporation in the InGaN layer on the HEMT template may be caused by the higher relaxation degree due to the compositional pulling effect. An increase in the growth temperature by 20 °C with optimized growth condition improves the crystalline quality of the InGaN, which is comparable to that on GaN/sapphire even if it is grown on a poor-quality GaN channel. [ABSTRACT FROM AUTHOR]

Abstract Internal polarizations, caused by the intrinsic material properties and lattice mismatch during material epitaxial growth, exist inherently in III-nitrides and limit significantly their practical applications. Here, InGaN/GaN single quantum well (SQW) structure grown on sapphire substrate was directly exfoliated by electrochemical (EC) etching. The separated InGaN/GaN SQW heterostructure membranes (SQW-HMs) exhibit substantial relaxation of internal strain and polarization compared to the as-grown samples. To further modulate/tune the internal polarizations and corresponding opto-electronic properties of the SQW-HMs, the piezo-phototronic effect was introduced by applying external stress on the freestanding membrane under ultraviolet (UV) light illumination. The obtained photoluminescence (PL) intensity can be effectively modulated in different manners under tensile and compressive straining conditions. Energy diagrams of the SQW-HMs under free and straining conditions were carefully analyzed to illustrate the working mechanisms of the piezo-phototronic modulations. This research provides a new approach to optimize the performances of III-nitride devices and expand their further applications in optical communications and optical integration systems. Graphical abstract In this work, the piezo-phototronic effect is introduced to modulate the optical properties of the freestanding InGaN/GaN heterostructure membrane, the corresponding physical mechanisms are systematically analyzed. Image 1 Highlights • Electrochemical (EC) etching is utilized for direct fabrication of the freestanding InGaN/GaN single-quantum-well heterostructured membrane (SQW-HM). • The optical properties of the released HM, compared with the as-grown InGaN/GaN film, are obviously optimized due to the relaxation of intrinsic stress. • The piezo-phototronic effect study of the released SQW-HM is systematically performed and the corresponding mechanisms are illustrated by analyzing the energy diagrams. [ABSTRACT FROM AUTHOR]

Abstract We report the study of the fast rise time and decay time in the ps time scale of the excitonic luminescence of a multiple quantum well (MQW) heterostructure of InGaN/GaN, including the excitation density effect. These structures were proposed as ultrafast scintillators for soft X-ray detectors and particle beam diagnostics. Measurements were carried out with a Hadland Imacon 500 streak camera following excitation of the sample by laser pulses of few tens of µJ at 266 nm and 400 nm, with pulse duration less than 200 fs. The rise time of the detected MWQ luminescence was less than 10 ps, with a possible contribution from the detection system and signal collection geometry. The calibration and the signal processing techniques employed to fully exploit the time resolution of the detection system are also described. [ABSTRACT FROM AUTHOR]

In order to design and development efficient III-nitride based optoelectronic devices, technological processes require a major effort. We propose here a detailed review focussing on the etching procedure as a key step for enabling high date rate performances. In our reported research activity, dry etching of an InGaN/GaN heterogeneous structure was investigated by using an inductively coupled plasma reactive ion etching (ICP-RIE). We considered different combinations of etch mask (Ni, SiO2, resist), focussing on the optimization of the deep etching process. A GaN mesa process with an etching depth up to 6 µm was performed in Cl2/Ar-based plasmas using ICP reactors for LEDs dimen sions ranging from 5 to 150 µm². Our strategy was directed toward the mesa formation for vertical-type diode applications, where etch depths are relatively large. Etch characteristics were studied as a function of ICP parameters (RF power, chamber pressure, fixed total flow rate). Surface morphology, etch rates and sidewall profiles observed into InGaN/GaN structures were compared under different types of etching masks. For deep etching up to few microns into the GaN template, we state that a Ni or SiO2 mask is more suitable to obtain a good selectivity and vertical etch profiles. The optimized etch rate was about 200nm/min under moderate ICP conditions. We applied these conditions for the fabrication of micro/nano LEDs dedicated to LiFi applications.

Four InGaN/GaN multi-quantum well (MQW) samples with different InGaN quantum well growth rates grow via metal-organic chemical vapor deposition (MOCVD) system. The relationship between the growth rate and luminescence characteristics of multiple quantum wells is studied by analyzing the temperature-dependent photoluminescence (TDPL) spectra, and microscopy photoluminescence image. The results show that the uniformity and internal quantum efficiency (IQE) of the samples become better first and then deteriorate as the growth rate increases. Whether the growth rate is too high or too low, it will cause the uniformity and IQE of the sample to deteriorate. The following two reasons lead to poor material uniformity. When the growth rate is too slow, the mobility of In atoms is higher than that of Ga atoms, forming In enrichment on the sample surface; on the contrary, the migration time of atoms is not enough, and Ga atoms cannot move to the lattice site. We also find when the growth rate is 0.0125 nm s ^−1 , the sample has the best uniformity, and when the growth rate is 0.034 nm s ^−1 , the IQE of the sample is the highest at room temperature.

The electronic and optical properties of indium-graded semipolar quantum well (QW) structures with different indium variation schemes and well widths have been investigated by 6 × 6 k · p calculations. Both increasing the indium composition difference between the maximum and the minimum points in the well layer and moving the location of the maximum indium composition in the opposite direction of the built-in field existing in the well layer of indium constant semipolar QW can improve the overlap of electron and hole wave functions, as well as the intensity of spontaneous emission rate spectra for y'- polarization of the indium-graded semipolar QW. With the increasing well width, the overlaps of optimized indium-graded semipolar QWs decrease more slowly than those of the indium constant QW, and the optical polarization ratios py'x'of the semipolar QWs increase more slowly than those of the indium constant one.

Abstract In this paper, InGaN/GaN based multiple quantum well blue light emitting diodes have been optimized by varying Si doping concentrations and incorporating step-wise graded thickness in quantum barriers for achieving improved internal quantum efficiency. Optimized Si-doped barrier profile along with graded thickness in quantum barriers shows improved performance of light emitting diodes. The improvement in results may be attributed to the fact that grading made the transportation of holes more homogeneous, which inhibits the electron leakage and enhances the radiative recombination. [ABSTRACT FROM AUTHOR]

The efficiency droop characteristics of single quantum well (SQW) InGaN/GaN light-emitting diodes (LEDs) including the phase-space filling (PSF) effect are predicted by a three-dimensional (3-D) numerical simulation. The carrier transport is based on the solution of the 3-D non-linear Poisson and drift-diffusion equations for both holes and electrons. A modified formulation of the Shockley—Reed–Hall (SRH) coefficient is proposed to describe the SRH carrier lifetime behavior, which increases at a low excitation level and decreases at a higher one. The current crowding causes a non-uniform distribution of the carrier concentration in the active layer that leads to the inversion of the local internal quantum efficiency (IQE) under the n-pad region when the injection current density increases from low to high levels. To further understand the correlation of the efficiency droop with the PSF effect, we systematically investigate carrier transport in the SQW InGaN/GaN LEDs and how the different PSF effect coefficients affect the current–voltage curve and IQE. The lumped IQE found in this study agrees well with previous experimental measurements. Moreover, the PSF effect has a strong impact on the IQE behavior including its peak and droop in efficiency. [ABSTRACT FROM AUTHOR]

Two kinds of substrates, sapphire and AlN/sapphire template (AlN template), are used for the growth of InGaN/GaN multi‐quantum‐well solar cell structures by metalorganic chemical vapor deposition, and their material and device properties are investigated. The results show that the samples grown on AlN template have a better crystal quality with a larger in‐plane compressive strain than those on sapphire, and solar cells fabricated on sapphire mostly exhibit better performance than those on AlN template. An analysis of the photoluminescence measurements indicates that a critical InGaN well thickness related to the generation of nonradiative recombination centers, which affects the internal and external quantum efficiencies, is thinner in samples grown on AlN template than in samples on sapphire. The critical thickness is speculated to be related to the large in‐plane compressive strain in the samples on AlN template. By contrast, in comparison between samples with a sufficiently thin InGaN well thickness of 1.0 nm, the sample on AlN template exhibits better solar cell performance than on sapphire. This implies that the improved crystal quality contributes to the improvement of internal quantum efficiency as long as the well layer is thinner than the critical thickness. [ABSTRACT FROM AUTHOR]

InGaN ternary alloys with their band gaps varying from 0.7 to 3.4 eV, are very promising for photodetector devices operating from UV to IR wavelength range. Using Silvaco–Atlas software, an In0.1Ga0.9N/GaN based p–i–n photodiode is designed and the J–V characteristics, the spectral responsivity, the frequency response and the cut‐off frequency as a function of InGaN thickness are studied. The photodiode exhibits a high reverse breakdown voltage of 38 V, a peak responsivity of 0.2 A W−1 at 0.343 μm wavelength and a cutoff frequency of 400 MHz under an applied reverse bias voltage of 2 V and for a 0.1 μm i‐InGaN layer, in good agreement with simulated and experimental results found in literature. It is found that an optimum i‐layer thickness of 1.5 μm for the maximum cutoff frequency of 4 GHz attributed to the predominance of the limitation in capacitance effect on the cutoff frequency at low i‐layer thickness and the transit time on the cuttoff frequency for high i‐layer thickness. For this i‐layer thickness, the highest peak responsivity about 0.244 A W−1 at 0.384 μm wavelength is achieved. [ABSTRACT FROM AUTHOR]