Light-emitting Diodes Samples Research Articles

Enhanced Optical–Thermal Performances of High-Power LED by Plated Copper on Thick Film Ceramic Substrate

Thick printed ceramic substrate (TPC) is a promising technique for the packaging of high-power light-emitting diode (LED). Nevertheless, the incorporation of glass phase and voids in the sintered Ag layer decrease the electrical conductivity and heat dissipation of TPC substrate, which contributes to an increase in the junction temperature of LED. This article demonstrates a novel packaging design to plate copper on the sintered Ag layer of TPC substrate, which was applied to enhance the optical–thermal performances of high-power LED. After plating, the copper layers are well bonded with the Ag layer and the sheet resistance decreases rapidly. With the plated copper on thick film (PCTF) substrate package, the total thermal resistance is 17.45% lower than that with TPC package, while the junction temperature change of LED samples is 8.04 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C and 9.92 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C, respectively. Moreover, the surface temperature of LED sample packaged with PCTF is 11.16% lower than that with TPC at the working current of 1600 mA, and the optical power is 4.79% and 3.2% higher at the working current of 400 and 1200 mA, respectively. The results demonstrate that the optical–thermal performances of LED are enhanced by using the PCTF substrate due to its excellent heat dissipation.

Flicker Modeling of White Light Emitting Diode With Sinusoidal Waveform

Based on the properties of light emitting diode (LED) source and driver, this article proposes a prediction model for the dynamic optical properties of LED sources. With a series of parameters for LED device (heatsink temperature, thermal resistance of LED source, heat dissipation coefficient, coefficients of luminous efficacy, and LED numbers) and driver (frequency and power amplitude), it is possible to accurately quantify dynamic light output of LED source and then to predict the flicker index and percent flicker. Optical and thermal evaluations are included in the modeling, which makes it easy for LED designers to comply with the regulations. Experimental validation of the proposed prediction model has been carried out using LED samples. It appears that the agreement between measured and calculated results of LED sources is fairly good with an average relative error of 5.3%.

Evaluation of Commercial Meat Products of Red Chicken Reared under LED Lights.

Simple SummaryThe aim of the study was to investigate the role of three different light-color temperatures of Light-Emitting Diodes (LEDs) (Neutral, Cool and Warm) on some attributes of breast meat. Various changes were observed in the physical and chemical characteristics of breast meat samples and the results obtained in fatty and volatile profiles indicate that the LEDs change the characteristics of meat.The objective of our study was to investigate the role of three different light-color temperatures of Light-Emitting Diodes (LEDs) [Neutral (); Warm () and Cool ()] on the qualitative attributes of breast meat obtained from male AZ Extra Heavy Red chickens. The comparison was made with meat deriving from chickens reared in the presence of classic neon lighting (Control). The meat was analyzed for the determination of both physical and chemical properties (cooking loss, moisture, total lipids and fatty acid composition). Furthermore, meat samples subjected to cooking were also analyzed for the identification of volatile compounds produced during the process; such evaluation was performed both immediately after cooking (T0) and after 7 days (T7) of cooked-meat storage at 4 °C. Cooking-loss values were higher for samples from chickens raised with Neutral LED (p < 0.05) compared to the other groups. For the fatty acid profiles of the meat, higher values were found for monounsaturated fatty acids (MUFAs) such as C18:1, C9 and C16:1 in Cool LED compared to the Control. Regarding the volatile profile of cooked meat, compounds belonging to the families of aldehydes, alcohols, ketones, and aromatic compounds were identified. Compounds belonging to the aldehyde family, such as hexanal, increased in Cool LED samples at T0 in comparison to the Control. On the other hand, the amounts of 1-Pentanol, 1-Octanol and 2-Octen-1-ol, which belong to the alcohol family, increased at T7 in Cool LED samples compared to the Warm LED. In conclusion, LED lighting showed to be effective in inducing significant variations on chicken breast meat ready to be introduced to the market, in particular regarding fatty acid profiles and the accumulation of volatile compounds. However more in-depth evaluation is needed for the identification of modifications regarding the sensorial sphere, which could have an impact on the consumer acceptability of the product.

Strain Compensation and Trade-Off Design Result in Exciton Emission at 306 nm from AlGaN LEDs at Temperatures up to 368 K.

In this study, we suppressed the parasitic emission caused by electron overflow found in typical ultraviolet B (UVB) and ultraviolet C (UVC) light-emitting diodes (LEDs). The modulation of the p-layer structure and aluminum composition as well as a trade-off in the structure to ensure strain compensation allowed us to increase the p-AlGaN doping efficiency and hole numbers in the p-neutral region. This approach led to greater matching of the electron and hole numbers in the UVB and UVC emission quantum wells. Our UVB LED (sample A) exhibited clear exciton emission, with its peak near 306 nm, and a band-to-band emission at 303 nm. The relative intensity of the exciton emission of sample A decreased as a result of the thermal energy effect of the temperature increase. Nevertheless, sample A displayed its exciton emission at temperatures of up to 368 K. In contrast, our corresponding UVC LED (sample B) only exhibited a Gaussian peak emission at a wavelength of approximately 272 nm.

Performance improvement of InGaN LEDs by using strain compensated last quantum barrier and electron blocking layer

The influence of u-AlGaN/InGaN superlattices (SLs) last quantum barrier (LQB) and p-AlGaN/InGaN SLs electron blocking layer (EBL) on the performance of InGaN light-emitting diodes (LEDs) are analyzed experimentally and theoretically. Research results indicated that LED C with u-AlGaN/InGaN SLs LQB and p-AlGaN/InGaN SLs EBL exhibit the highest output power among the three groups of LED samples. At 200 mA, the output power of LED C is enhanced by 27.5% as compared with that of reference LED A with u-GaN LQB and p-AlGaN/GaN SLs EBL. The efficiency droop of LED C has also been suppressed effectively. At 200 mA, the efficiency droop of LED C was 28.5%, which was smaller than that of LED A 34%. By analyzing the distribution of electron/hole concentration in multiple quantum wells, it is indicated that the leakage of electrons from the active layer can be effectively reduced and the injection efficiency of holes into the active layer can be dramatically enhanced by using strain compensated AlGaN/InGaN SLs LQB and EBL. The reason is that the potential energy barriers for electrons and holes could be effectively regulated by using the strain compensated LQB and EBL, which is consistent with simulation results of energy band diagram.

Improvement of Radiative Recombination Rate and Efficiency Droop of InGaN Light Emitting Diodes with In‐Component‐Graded InGaN Barrier

The influences of In‐component‐graded InGaN barrier on the performances of InGaN light emitting diodes (LEDs) are studied. The results show that LEDs with In‐component linearly graded InGaN barrier exhibit better performances of radiative recombination rate and efficiency droop than reference LED with constant‐In‐component InGaN barrier. At 150 mA, the external quantum efficiencies for LED A with constant‐In‐component InGaN barrier, LED B with the In‐component linearly increasing in the InGaN barrier, and LED C with the In‐component linearly decreasing in the InGaN barrier are 30.30%, 36.66%, and 34.03%, respectively. Among the three sets of LED samples, LED B, with the In‐component linearly increasing in the InGaN barrier, has the highest radiative recombination rate due to suppression of quantum confinement stark effect and enhancement of carrier confinement effect in the active layer. The efficiency droop for LED A, LED B, and LED C is 34.83%, 25.67%, and 16.67%, respectively. Analysis indicates that the efficiency droop is mainly determined by the hole injection efficiency and electron leakage from the active layer. LED C with the In‐component linearly decreasing in the InGaN barrier has the lowest efficiency droop due to improved hole injection efficiency and reduced electron leakage.

Luminescence properties of InGaN/GaN light-emitting diodes with violet, blue, and green emission

The optical properties of InGaN/GaN light-emitting diodes (LEDs) grown at various temperatures were investigated using photoluminescence (PL) and time-resolved PL spectroscopies. The indium inhomogeneity generated localized states in InGaN/GaN quantum wells, and these affected the carrier dynamics. InGaN/GaN LED samples containing different indium contents were grown at temperatures of 900, 876, and 820 °C, resulting in violet, blue, and green emission, respectively. The violet LED sample exhibited the strongest PL intensity and the shortest PL decay time. This finding was attributed to an enhanced overlap of the electron and the hole wavefunctions, attributable to a reduced quantum-confined Stark effect due to the low indium contents in the violet LED. The PL decay times became longer with increasing emission wavelength, which can be explained by carrier transfer from weakly localized states to strongly localized states. These results indicate that the luminescence properties and the carrier dynamics of InGaN/GaN LEDs are affected by the growth temperature.

Ultraviolet Light-Emitting Diodes Using Aluminium Indium Nitride Nanowire Structures

Ultraviolet (UV) light-emitting diodes (LEDs) have various applications in the field of biochemistry, medicine, water/air purification, etc. To achieve efficient UV LEDs, researchers have essentially focused on the use of AlGaN alloys in the active region. However, the practical applications of AlGaN based UV LEDs are severely limited due to poor external quantum efficiency (EQE). Some reasons behind the low EQE in AlGaN based UV LEDs are efficiency droop, mostly due to electron leakage into the p-region, poor light extraction efficiency (LEE) which is mainly due to the total internal reflection and the absorption of UV light in the p-GaN contact layer. Identifying and developing the potential of alternative UV materials will be critical to make further progress in the development of deep UV emitters. In this regard, AlxIn1-xN alloy has not been widely studied even though it holds great potential applications in UV and visible light-emitting devices [1]. In this study, we have performed the epitaxial growth, electrical and optical properties of spontaneously grown AlInN nanowires on Si (111) substrate by molecular beam epitaxy (MBE) and demonstrated a high crystalline quality of AlInN nanowire LED structures with stable and strong EL emission at ~299 nm peak wavelength.The AlInN nanowire LED structure, shown in Fig. 1(a), was spontaneously grown on n-Si (111) substrates under nitrogen rich conditions by a Veeco GEN II MBE system equipped with a RF plasma-assisted nitrogen source. The growth conditions for GaN nanowire segments include a growth temperature of ~ 770 °C, nitrogen flow rate of 1 sccm, and forward plasma power of ~ 400 W. The device active region consists of ~ 100 nm n-Al0.78In0.22N, 40 nm undoped Al0.75In0.25N well and 100 nm p-Al0.78In0.22N layers. Growth temperature of the active region was at ~ 670 ̶ 700 °C to increase the In incorporation in AlInN segments and the nitrogen flow rate was kept at 2.5 sccm, while the plasma power was fixed at 400 W. After being grown by MBE, the nanowire LED samples were fabricated using standard lithography method as reported elsewhere [2]. The device characterization was performed on LED with an area size of 500×500 µm2. Photoluminescence (PL) spectrum of the grown nanowire LEDs exhibits strong emission in the UV wavelength range as shown in Fig. 1(b). The peak emission at ~ 299 nm and ~ 280 nm is responsible for the emission from the AlInN quantum well and barriers, respectively. The AlInN nanowire UV LEDs have strong EL intensity with the peak wavelength at ~ 299 nm, as shown in Fig. 1(c). This work is being developed toward the achievement of high power AlInN nanowire UV LEDs, and the result will be presented. Reference R. T. Velpula, B. Jain, M. R. Philip et al., Sci. Rep., 10(1) 1-10 (2020).R. T. Velpula, B. Jain, H. Q. T. Bui et al., Optical Materials Express, 10(2) 472-483 (2020) Figure 1

Joint evaluation of internal quantum efficiency and light extraction efficiency for AlGaN-based deep ultraviolet LEDs considering optical polarization properties

In this work, a joint evaluation method for the internal quantum efficiency (IQE) and light extraction efficiency (LEE) for AlGaN-based deep ultraviolet (DUV) light emitting diodes (LEDs) is proposed by fully considering the optical polarization properties. In this method, the IQE curve varying with the forward current can be reconstructed from a few measurement data at a small injection level. The corresponding LEE can be determined using the composition of spontaneous emission light with transverse electric and transverse magnetic components at different forward currents. The proposed method is applied for the efficiency evaluation of the AlGaN-based LED sample and verified by comparing with the EQE result deduced from the measured light output power–current (L–I) characteristic. It is demonstrated that the very low EQE and significant efficiency droop is from not only IQE but also LEE for AlGaN-based DUV LEDs.

Temperature Sensing Characteristics and Long Term Stability of Power LEDs Used for Voltage vs. Junction Temperature Measurements and Related Procedure

A detailed study about the direct measurement of junction temperature Ti of off-the-shelf power light emitting diodes (LED) is presented. The linear dependence on temperature of the voltage drop across the device terminals at a constant current is in particular exploited and fully characterized, in the temperature range from T = 35 °C to 135 °C, with tests repeated at one thousand different probe currents. The accurate experimental data, obtained on several LED samples bearing two different part numbers, are reported, showing that they exhibit a high degree of linearity in wide current ranges, a circumstance that allows for a fast and reliable calibration as sensors. The measurement error is also fully characterized in terms of repeatability and stability over time, with measurements repeated after 600, 900, 1200 and 1800 hours of applied electro-thermal stress, demonstrating that the relevant sensor parameters stabilize after a few hundred hours of operation. A full set of parameters is provided for the two device models, allowing the direct use of each LED for the self-monitoring of the junction temperature and ensure compliance with their safe operating area over time. Moreover, a procedure and a simple circuit for the real time measurement of Ti, while the LED is on, are presented. The procedure does not require a stable current source, and relies instead on the application of a sub-threshold current ramp for such a short time that the change in the output light is not perceived by human eyes.

Fingerprinting light emitting diodes using spectrometer

Fingerprinting refers to a class of techniques to distinguish products using their unique features originated during production. Fingerprinting has a wide range of applications including supply-chain integrity and device authentication. The authors propose the first fingerprinting technique of light-emitting diode (LED), which is pervasively used in electronics products. The key idea is to use spectral features of LEDs obtained by a spectrometer. Combined with a machine-learning classifier, the proposed method successfully distinguishes ten individual LED samples from the same lot at 99% accuracy.

Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be ~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the quantum well and the inhomogeneous carrier distribution in the MQWs. The difference in the internal electric field of the MQW between the LED on silicon and sapphire could be a major reason for the difference in the effective active volume, and consequently, the efficiency droop.

Implementation of phosphor sedimentation to reduce thermal instability issue affecting white LED luminescence

Purpose In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous efficacy and spectral characteristic of white LED are dependent on the temperature, causing thermal effects on luminous efficacy and color shift of white LED become a critical application checkpoint to be addressed by white LED manufactures. Thus, the purpose of this paper is to minimize the thermal stability issue affecting white LED luminescence during operation by introducing phosphor sedimentation process. Design/methodology/approach The LED samples were assembled and sent for centrifugation with 0, 5 and 10 revolutions per second (rps), respectively, during phosphor sedimentation process. Luminescence properties of these LED samples were then characterized at a varying temperature to investigate the effect of phosphor sedimentation on the luminescence stability of LED samples. The LED samples were also cross-sectioned and analyzed to understand the phosphor sedimentation mechanism. Computational fluid dynamics (CFD) was applied to study the temperature distribution of the non-phosphor sediment (NPS) and phosphor sediment (PS) LED during operation to validate the hypotheses based on experimental data. Findings Experimental results show that the luminous intensity of PS LED samples degrades less significant at high temperature. The experimental results also show that the color coordinate for PS LED samples is more stable and is less blue-shifted than NPS LED samples as the temperature increased. These are because the heat generated by phosphor particles during operation can be dissipated effectively throughout a high thermal conductivity substrate after phosphor sedimentation. Thus, the phosphor temperature of PS LED is lower than NPS LED during operation as validated with the thermal simulation. Practical implications The study of this paper is applicable as a reference for industries who intend to resolve the thermal stability of white LED during operation. The luminescence properties changes as a function of the temperature study in this paper can be used to predict the application performances of white LED accurately. Apart from that, the analysis method of temperature distribution using CFD simulations can be extended by other CFD users in the future. Originality/value Implementation of phosphor sedimentation to reduce thermal instability issue of white LED has yet to be reported on previous studies. Most literature just studied the thermal instability issue of either assembled LED or raw material, without suggesting any solution to tackle the issue.

Effect of a thin Au and ZnO layer on optical properties of 1D PhC structures patterned in LED surface

1D patterns with different periods were fabricated by Electron Beam Direct Write (EBDW) lithography with the aim to improve the Light Emitting Diode (LED) efficiency, i.e. the light out coupling. Three sets of 1D PhC LED samples with bare PhC, thin Au, and ZnO layers were prepared. The highest Light Extraction Enhancement (LEE) was achieved for 600 nm Photonic Crystals (PhC) period in the case of bare and Au deposited PhC, and for 500 nm PhC period in the case of ZnO deposited PhC, respectively. LEE was studied by measuring L-I characteristics of untreated reference LEDs compared to patterned LEDs.

Confocal photoluminescence investigation to identify basal stacking fault\u2019s role in the optical properties of semi-polar InGaN/GaN lighting emitting diodes

High spatial-resolution confocal photoluminescence (PL) measurements have been performed on a series of semi-polar (11–22) InGaN light emitting diodes (LEDs) with emission wavelengths up to yellow. These LED samples have been grown on our high crystal quality semi-polar GaN templates which feature periodically distributed basal stacking faults (BSFs), which facilitates the study of the influence of BSFs on their optical performance. Scanning confocal PL measurements have been performed across BSFs regions and BSF-free regions. For the blue LED, both the emission intensity and the emission wavelength exhibit a periodic behavior, matching the periodic distribution of BSFs. Furthermore, the BSF regions show a longer emission wavelength and a reduced emission intensity compared with the BSF-free regions. However, with increasing indium content, this periodic behavior in both emission intensity and emission wavelength becomes weaker and weaker. When the indium content (and correspondingly, wavelength) increases up to achieve yellow emission, only random fluctuations have been observed. It is worth highlighting that the influence of BSFs on the optical properties of semi-polar InGaN LEDs is different from the role of dislocations which normally act as non-radiative recombination centers.

Growth and characterization of amber light-emitting diodes with dual-wavelength InGaN/GaN multiple-quantum-well structures

We report the growth of a dual-wavelength green-amber light-emitting diode (LED) structure. Such dual-wavelength multiple quantum wells (MQWs) structures not only assisted the releasing of the strain, accordingly improved the crystal quality of MQW heterointerfaces, but also enhanced the incorporation of indium atoms amid growth of the high indium-content QWs. The high-resolution x-ray diffraction (HR-XRD) measurement showed multi-order satellite peaks, implying the abrupt heterointerfaces formed between MQWs in the LED sample. It shows a distinct dual wavelength emission characteristics in the temperature-dependent photoluminescence (TDPL). Furthermore, only a single amber peak around 591–609 nm was emitted with a small blue shift at a current injection from 5 to 100 mA in the electroluminescence (EL) characterization. The full-width at half-maximum (FWHM) of these peaks just shows a little fluctuation.

Thermally stable lead-free phosphor in glass enhancement performance of light emitting diodes application.

A co-sintering method for preparing PIG is proposed, a Ce3+ doped yttrium aluminum garnet (YAG:Ce) phosphor in glass (PIG) slice is fabricated through co-sintering polycrystalline Ce:YAG phosphor, and a new, to the best of our knowledge, homemade matrix glass SiO2-K2O-BaO-B2O3 glass powder is detected to confirm crystal phase by X-ray powder diffractions (XRD) and micromorphology by scanning electron microscope (SEM). The YAG:Ce phosphor particles dispersed in the matrix are vividly observed and their distributions are relatively uniform. The PIG packaged light-emitting diode (LED) sample shows a relatively lower correlated color temperature (CCT) than the conventional phosphor-dispensing LED sample. White light can be achieved in the PIG slice under 465nm LED excitation by controlling the phosphor concentration or thickness. The highest luminous efficacy of the PIG slice packaged white LED is 94.67lm/W at 100mA. Controllable geometrical and optical properties of the YAG:Ce PIG can generate evident improvements in the manufacturing of identical CCTs for high-power white LEDs. The combination of PIG with a blue LED chip of a specific wavelength, if measured before final assembly, enables targeted production of specific CCT white LEDs. PIG technology allows the realization of high stability and thermal conductivity for the phosphor layer. This simple method provides many possibilities for LED packaging, including thin film flip chip and remote phosphor technology.

Effects of three-dimensional strain distribution on the performance of GaN-based light-emitting diodes on patterned sapphire substrates

Depth-resolved confocal Raman and micro photoluminescence (PL) are adopted to analyze GaN-based light-emitting diodes (LEDs) with an ex situ sputtered AlN nucleation layer on patterned sapphire substrates (PSSs). The strain on PSSs is measured by Raman spectral mapping, and the results demonstrate that the strain distribution within the LED structures strongly correlates to the pattern array of the PSS. Cone regions with less dislocations have lower strain than plane regions. The array pattern of the PSS’s surface can directly affect strain existing in the later crystal growth even at the position of the layer before the p-GaN growth. Moreover, the two-dimensional micro-PL mapping of the GaN-based LED samples on a PSS reveals a close relationship with the strain distribution on the sample surface. It is found that the strain as well as the PL intensity difference can be mitigated by proper pre-strained layers in order to realize high efficiency LEDs.

Comparison of the Changes in Luminescence Properties Between Cool White and Warm White LEDs at Varying Temperatures

The changes of luminescence properties in cool white (CW) and warm white (WW) light-emitting diodes (LEDs) in response to operating temperatures are compared in this paper. In addition, the emission spectrum of blue LED chips was characterized under the same experimental conditions for cross-reference analysis. The yellow YAG (Y3Al5O12:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) and red nitrididosilicate (Sr2Si5N8:Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) phosphors were synthesized in-house and packed at different concentration configurations to create LED samples of correlated color temperature 6500 K for CW LEDs and 2700 K for WW LEDs. The emission spectrum measurements showed drastic decrements of light emission intensities for both CW and WW LED samples at elevated temperature. Both CW and WW LED samples tend to have more bluish hue with increasing temperatures. Furthermore, the trend of color rendering index (CRI) changes of CW and WW LEDs has differed, a finding that is not commonly reported in other studies. The CRI of CW LED samples increased, whereas the CRI of WW LED samples decreased at elevated temperature. This is due to different shift directions of peak emission wavelength in yellow Y3Al5O12:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and red Sr2Si5N8:Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> phosphors.

Temperature Dependence of Efficiency Droop in GaN-based Blue Light-emitting Diodes from 20 to 80°C

We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to 80°C. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to 80°C, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.