Abstract:In this study, we demonstrated high efficiency InGaN/GaN light emitting diodes (LEDs) with asymmetric triangular multiple quantum wells (MQWs). Asymmetric triangular MQWs not only contribute to uniform carrier distribution in InGaN/GaN MQWs but also yield a low Auger recombination rate. In addition, asymmetric triangular MQWs with gallium face-oriented inclination band profiles can be immune from the polarization charge originating from typical c-plane InGaN/GaN quantum well structures. In the experiment, LEDs… Show more
“…The SRH and Auger recombination coefficients are 20 ns and 1.5 × 10 30 , which are similar to the reported literature [34]. Both of the recombination coefficients are reported to be smaller in the graded quantum wells than the regular quantum wells by roughly a factor of half [13,35]. Other simulation parameters, such as mobility, temperature, and background losses are the same as reported in the literature [23].…”
supporting
confidence: 87%
“…The defect-assisted Shockley-Read-Hall (SRH) recombination rate is reduced by more than half and the Auger recombination rate is estimated to be negligible in comparison to the R-LED. The comparatively reduced SRH recombination and Auger recombination rates of W-LED is supported by earlier experimental and theoretical reports [13,35]. The rate of Auger recombination has been reported to be higher in rectangular wells than softened or graded wells, hence reducing the device efficiency [35].…”
Section: Resultssupporting
confidence: 55%
“…The IQE peak of R-LED and W-LED occurs at ~0.18 µA·cm −2 and ~0.17 A·cm −2 respectively. The IQE peak in W-LED is shifted to higher current density, which is typically a case in graded LEDs [8,13]. This shift of IQE peak or droop onset is desirable in improving the device performance [2].…”
Section: Resultsmentioning
confidence: 99%
“…There are multiple reports to improve the IQE of LEDs mainly by using nonpolar substrates [4,5] and bandgap engineering [6][7][8][9]. Salient bandgap engineering approaches include triangular-shaped quantum wells [10,11], staggered quantum wells [12], graded quantum wells [8,13], polarization-matched quaternary barriers [14,15], quaternary electron blocking layer (EBL) [16], modification of EBL [17,18], InGaN barriers [19,20], as well as last quantum barrier [21], coupled quantum wells [22], and recently proposed all-quaternary device with and without electron-blocking layer [23,24]. In comparison to the conventional rectangular quantum wells, it has been shown using triangular, staggered, dip-shaped, and trapezoidal wells that the electron-hole wavefunction overlap is significantly improved in the quantum wells (QWs), which leads to improved optoelectronic output of the device [11,[25][26][27].…”
To improve the internal quantum efficiency of green light-emitting diodes, we present the numerical design and analysis of bandgap-engineered W-shaped quantum well. The numerical results suggest significant improvement in the internal quantum efficiency of the proposed W-LED. The improvement is associated with significantly improved hole confinement due to the localization of indium in the active region, leading to improved radiative recombination rate. In addition, the proposed device shows reduced defect-assisted Shockley-Read-Hall (SRH) recombination rate as well as Auger recombination rate. Moreover, the efficiency rolloff in the proposed device is associated with increased built-in electromechanical field.
“…The SRH and Auger recombination coefficients are 20 ns and 1.5 × 10 30 , which are similar to the reported literature [34]. Both of the recombination coefficients are reported to be smaller in the graded quantum wells than the regular quantum wells by roughly a factor of half [13,35]. Other simulation parameters, such as mobility, temperature, and background losses are the same as reported in the literature [23].…”
supporting
confidence: 87%
“…The defect-assisted Shockley-Read-Hall (SRH) recombination rate is reduced by more than half and the Auger recombination rate is estimated to be negligible in comparison to the R-LED. The comparatively reduced SRH recombination and Auger recombination rates of W-LED is supported by earlier experimental and theoretical reports [13,35]. The rate of Auger recombination has been reported to be higher in rectangular wells than softened or graded wells, hence reducing the device efficiency [35].…”
Section: Resultssupporting
confidence: 55%
“…The IQE peak of R-LED and W-LED occurs at ~0.18 µA·cm −2 and ~0.17 A·cm −2 respectively. The IQE peak in W-LED is shifted to higher current density, which is typically a case in graded LEDs [8,13]. This shift of IQE peak or droop onset is desirable in improving the device performance [2].…”
Section: Resultsmentioning
confidence: 99%
“…There are multiple reports to improve the IQE of LEDs mainly by using nonpolar substrates [4,5] and bandgap engineering [6][7][8][9]. Salient bandgap engineering approaches include triangular-shaped quantum wells [10,11], staggered quantum wells [12], graded quantum wells [8,13], polarization-matched quaternary barriers [14,15], quaternary electron blocking layer (EBL) [16], modification of EBL [17,18], InGaN barriers [19,20], as well as last quantum barrier [21], coupled quantum wells [22], and recently proposed all-quaternary device with and without electron-blocking layer [23,24]. In comparison to the conventional rectangular quantum wells, it has been shown using triangular, staggered, dip-shaped, and trapezoidal wells that the electron-hole wavefunction overlap is significantly improved in the quantum wells (QWs), which leads to improved optoelectronic output of the device [11,[25][26][27].…”
To improve the internal quantum efficiency of green light-emitting diodes, we present the numerical design and analysis of bandgap-engineered W-shaped quantum well. The numerical results suggest significant improvement in the internal quantum efficiency of the proposed W-LED. The improvement is associated with significantly improved hole confinement due to the localization of indium in the active region, leading to improved radiative recombination rate. In addition, the proposed device shows reduced defect-assisted Shockley-Read-Hall (SRH) recombination rate as well as Auger recombination rate. Moreover, the efficiency rolloff in the proposed device is associated with increased built-in electromechanical field.
“…Smooth confining potential can also be made through a linear decrease of In composition along the growth direction of InGaN/GaN QWs. This can have better spread of carriers among QWs and transportation of holes which results in improvement of quick drop of EQE and light output power [25–30]. Fig.…”
The features of eight-period In0.2Ga0.8N/GaN quantum wells (QWs) with silicon (Si) doping in the first two to five quantum barriers (QBs) in the growth sequence of blue light-emitting diodes (LEDs) are explored. Epilayers of QWs’ structures are grown on 20 pairs of In0.02Ga0.98N/GaN superlattice acting as strain relief layers (SRLs) on patterned sapphire substrates (PSSs) by a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. Temperature-dependent photoluminescence (PL) spectra, current versus voltage (I-V) curves, light output power versus injection current (L-I) curves, and images of high-resolution transmission electron microscopy (HRTEM) of epilayers are measured. The consequences show that QWs with four Si-doped QBs have larger carrier localization energy (41 meV), lower turn-on (3.27 V) and breakdown (− 6.77 V) voltages, and higher output power of light of blue LEDs at higher injection current than other samples. Low barrier height of QBs in a four-Si-doped QB sample results in soft confinement potential of QWs and lower turn-on and breakdown voltages of the diode. HRTEM images give the evidence that this sample has relatively diffusive interfaces of QWs. Uniform spread of carriers among eight QWs and superior localization of carriers in each well are responsible for the enhancement of light output power, in particular, for high injection current in the four-Si-doped QB sample. The results demonstrate that four QBs of eight In0.2Ga0.8N/GaN QWs with Si doping not only reduce the quantum-confined Stark effect (QCSE) but also improve the distribution and localization of carriers in QWs for better optical performance of blue LEDs.
Over the last decades, continuous technological advancements have been made in III‐nitride light‐emitting diodes (LEDs), so that they are considered as a promising replacement of traditional light sources. With the emission wavelength covering the entire visible spectrum, InGaN LEDs find various applications such as solid‐state lightings, full‐color displays, and visible light communication. However, the quantum efficiency of InGaN LEDs suffers from a dramatic decline as the emission wavelength extends from blue to green–red region. This issue restrains the lighting and display applications based on the color‐mixing monolithic lighting source system. In this review, the recent breakthroughs in long‐wavelength InGaN LEDs, together with the challenges and approaches to realize high‐indium‐composition InGaN epilayers, are introduced. These cover the different epitaxial substrates, nucleation layers, and epitaxial structures, especially multiple quantum wells active region. The related studies are also discussed to improve the long‐wavelength LEDs performance from the aspect of crystal quality, growth orientation, carrier‐injection, and 3D nanostructures. Finally, current status and perspectives for future long‐wavelength LEDs development are proposed briefly.
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