Effects of saturation of nonradiative recombination centers on internal quantum efficiency in InGaN light-emitting diodes
9
Citation
33
Reference
10
Related Paper
Citation Trend
Abstract:
The internal quantum efficiency (IQE) of InGaN near-UV light-emitting diodes with different threading dislocation densities (TDDs) was studied by using excitation power density and temperature-dependent photoluminescence spectroscopy. The IQE was evaluated as functions of excitation density and temperature under band-to-band and selective excitation of the InGaN active layers. The IQE curves under weak excitation densities were analyzed with a rate equation model of radiative and nonradiative recombination of excitons, in which the exciton localization and the filling of nonradiative recombination centers (NRCs) were considered. Based on the analysis, we discussed the effects of filling NRCs on the IQE as functions of TDD and temperature and we clarified that the increase in the IQE at lower excitation densities was caused by filling NRCs. The analysis also indicated whether the maximum IQE value reached 100% at low temperatures.Keywords:
Quantum Efficiency
Saturation (graph theory)
국내 LEDs 산업의 발달함에 따라 LEDs 가격이 지속적으로 낮아지며 광량과 내구성이 좋은 LEDs가 개발되어 불량한 기후 조건에서 작물의 수량을 증진하기 위하여 시설재배 농가를 중심으로 원예작물에 LEDs 이용을 위한 시도가 이뤄지고 있다. 이에 본 실험은 적색과 초적색 LEDs 보광이 ``홍로``/M.26 사과의 과중분포 및 과실품질에 미치는 영향을 구명하여 사과에서 LEDs 보광이 과실의 품질향상에 도움이 될수 있는지를 구명하기 위하여 실험하였다. 실험 처리는 대조구인 무처리구, 적색광(660nm) 2, 4시간 조사구, 초적색광(730nm) 2, 4시간 조사구의 5처리를 난괴법 3반복으로 실험하였다. LEDs 보광은 일몰후 처리별로 조사하였으며 처리시기는 화아분화기와 착색기에 각각 1개월씩 보광하였다. 실험결과 적색광 LEDs 보광에 의해 대조구에 비해 적색 LED 처리구에서 엽중이 늘어났으나 초적색 LEDs 보광에서는 엽중이 감소하였으며 보광시간이 길어질수록 더욱 감소하였다. 2009년에는 무처리구인 대조구에 비해 LEDs 처리구에서 과중이 증가하였으며 특히 적색광 LEDs 처리구에서 188g 이하의 소과 발생도 없었고 300g 이상 과실도 많았다. 2010년에는 250g 이상 과실이 대조구에 비해 적색광 2, 4시간 보광에서 증가하였으나 초적색광 보광에서는 대조구에 비해 감소하였다. 과실의 경도는 대조구에 비해 초적색광 2, 4시간 보광에서 증가하였으며 당도에서는 큰 차이를 나타내지 않았다. 착색도에 있어서는 적색 LEDs 처리구가 대조구에 비해 Hunter a 값이 낮아지는 경향을 나타냈으나 초적색광에서는 높아지는 경향을 나타냈다. 이상의 결과를 통해 살펴보면, 적색광은 홍로 사과의 과중을 증가시켰으나 초적색광은 Hunter a 값을 높이는 결과를 나타냈다. 이에 앞으로 사과원에서의 LEDs의 효과적인 이용을 위해 적색광과 초적색광 단용처리가 아닌 혼합처리를 하여 각각의 광원의 효과가 상승적으로 작용하는지에 대한 추가적인 연구가 필요할 것으로 판단되었다.
Cite
Citations (0)
We present a study of time-resolved photoluminescence (TRPL) measurements of n-type CdTe single crystals doped by a novel procedure. The measurements show that the surface recombination velocity of low doped n-type (n0=1.5×1016 cm−3) samples was below 200 cm/s and the nonradiative bulk recombination time was around 180 ns. By conducting the TRPL measurements under different carrier injection levels, it was found that radiative bulk recombination was the dominant mechanism in the low doped crystals. This enabled us to obtain the bulk radiative recombination rate constant, B, which was found to be 3±0.5×10−9 cm3 s−1.
Cadmium telluride photovoltaics
Carrier lifetime
Cite
Citations (60)
Annihilation
Biexciton
Cite
Citations (13)
Red micro-light-emitting diodes (μLEDs) have been generated significant interest for the next generation μLEDs displays. It has been shown that the external quantum efficiency (EQE) of AlInGaP red μLEDs markedly decreases as the size goes to very small dimension. Here, we demonstrate size-independent peak EQE of 611 nm InGaN red μLEDs. Packaged μLEDs show a peak EQE varied from 2.4% to 2.6% as the device area reduces from 100 × 100 to 20 × 20 μm2. These results demonstrate the promising potential for realizing high efficiency red μLED with very small size using InGaN materials.
Quantum Efficiency
Wide-bandgap semiconductor
Cite
Citations (52)
Near-ultraviolet (NUV) light-emitting diodes (LEDs) have been used in several potential applications such as UV curing and biochemical sensors. However, the internal quantum efficiency (IQE) of NUV-LEDs is still a crucial issue. To improve the IQE, in this paper, an asymmetric triangular multiple quantum well (MQW) structure was used, which exhibited a higher emission efficiency and lower efficiency droop with nitrogen face-oriented inclination. This is in contrast to the trend observed in blue LEDs. Furthermore, we demonstrated that holes are more confined in MQWs with nitrogen face-oriented inclination than in MQWs with gallium face-oriented inclination. Moreover, simulations revealed that the IQE improved by approximately 32% compared with that of symmetric square MQW NUV-LEDs; this trend was also confirmed through experimental results. The external quantum efficiency of thin-film flip-chip LEDs with nitrogen face-oriented inclination MQWs was 52%.
Quantum Efficiency
Indium gallium nitride
Ultraviolet
Wide-bandgap semiconductor
Cite
Citations (13)
We report the internal quantum efficiency (IQE) and external quantum efficiency (EQE) of m-plane InGaN-based LEDs and c-plane LEDs emitting at 400 nm. According to excitation density dependent photoluminescence (PL) measurements, the IQE values for the m-plane LEDs are approximately 70% higher than that for c-plane reference LEDs with the same structure (multiple-quantum well active region with 3nm In0.01Ga0.99N barriers) and similar emission wavelength (400nm) albeit on sapphire substrate. Electroluminescence (EL) measurements reveal that the external quantum efficiency (EQE) from both LEDs shows negligible droop under electrical injection due to the employment of thin In0.01Ga0.99N barriers, i.e. coupled quantum wells, in the active regions. However, with increasing current, the EL intensity of the m-plane LEDs increases more rapidly than that of the c-plane LEDs, with the EL intensity reaching its peak value at ~240 Acm-2 for the m-plane LEDs and ~420 Acm-2 for the c-plane LEDs. Consistent with the IQE values obtained from the PL measurements, the m-plane LEDs exhibit ~ 60% higher EQE values than the c-plane counterparts. It is also worth to mention that increasing the emission wavelength (from 400 nm to 435 nm) for the m-plane LEDs does not affect the efficiency retention at high injection levels.
Quantum Efficiency
Cite
Citations (0)
Abstract Temperature variation of radiative recombination rate obtained for defect photoluminescence (PL) in high‐quality a‐Si:H after illumination of intense pulsed light is presented and compared with results previously reported for defective a‐Si:H films. We have not found significant difference between the temperature variation of the rate of radiative recombination at photo‐created radiative defects and that at native radiative defects. This fact suggests the recombination processes at the photo‐created defects and the native defects are similar. The temperature dependence of the radiative recombination rates in a‐Si:H is predicted by a model of the recombination processes for various cases of different density of deep and strongly localised tail states. Our recent experimental results for the principal PL and defect PL coincide with the prediction of the model. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non-radiative recombination
Recombination rate
Cite
Citations (4)
GaN-based light-emitting diodes (LEDs) with graded-thickness quantum wells and barriers (GMQW-LEDs) are fabricated and researched in this letter. The light power and carrier distribution of GMQW-LEDs are compared with those of LEDs with original uniform MQW (OR-LEDs), graded-thickness quantum wells (GQW-LEDs), and graded-thickness quantum barriers (GQB-LEDs) through numerical simulation, respectively. The experimental results show that light power of GMQW-LEDs is enhanced significantly compared with that of OR-LEDs. The simulation results reveal that GMQW-LEDs show light output power enhancements of 25.7%, 14.3%, and 9.2% compared with OR-LEDs, GQW-LEDs, and GQB-LEDs at current density of 100 A/cm 2 , respectively. This is due to the superior hole distribution in quantum wells, which inhibits the electron leakage and enhances the radiative recombination.
Quantum Efficiency
Wide-bandgap semiconductor
Cite
Citations (4)
We demonstrate a significant quantum efficiency enhancement of InGaN red micro-light-emitting diodes (μLEDs). The peak external quantum efficiency (EQE) of the packaged 80 × 80 μm2 InGaN red μLEDs was largely increased to 6.0% at 12 A/cm2, representing the significant process in exploring the efficiency of InGaN red μLEDs. The improvement of the EQE is attributed to the significant enhancement of the quantum efficiency, which is confirmed by the electron–hole wavefunction overlap in the InGaN quantum well from the band gap simulation and the photoluminescence intensity ratio at room temperature/low temperature. Ultrasmall 5 × 5 μm2 InGaN red μLEDs were also obtained, which show a high peak EQE of 4.5%. This work demonstrates a simple approach to achieving highly efficient InGaN red μLEDs, which are very promising candidates for ultrasmall red μLEDs required by AR/VR displays.
Quantum Efficiency
Cite
Citations (29)
A new evaluation method for effective internal optical power (IOP) and internal quantum efficiency (IQE) of light-emitting diodes (LEDs) is demonstrated. This method is based on the optical and thermal properties of LEDs. By using this proposed method, the effective IOP and the IQE of LEDs could be directly extracted from the measurements of external optical power (EOP) and junction temperature of LEDs. This method needs no assumption of the injection efficiency of carriers in the LEDs and no measurement-condition limitation of low current-injection level.
Quantum Efficiency
Optical power
Electrical efficiency
Cite
Citations (3)