Open Access
Add to BibSonomy
Abstract
Tamm plasmons (TPs), whose plasmon modes are confined at the Bragg reflector/metal interface due to the photonic stopband of the reflector and the negative dielectric constant of the metal, exhibit many advantages over the conventional surface plasmons (SPs) and potential applications in sensors, filters, optical circuits and light-emitting devices. In this paper, a TP-cavity structure has been proposed for accelerating the light emission and alleviating the large metal loss, which is hopeful for solving the efficiency droop and “green gap” problems in InGaN green light-emitting diodes (LEDs). The light emission performance of TP-cavity LEDs was systematically investigated based on transfer matrix and finite-difference time domain methods. Purcell factor (Fp) and light extraction efficiency (LEE) were both remarkably enhanced, which would be attributed to the presence of the TP and/or SP modes induced by the TP-cavity structure. In addition, two important factors including the thicknesses of the top Ag film and medium layer were investigated in detail and taken into account for the balance between the Fp and the LEE. Finally, light emission intensity was significantly enhanced for the TP-cavity green LEDs after the structure optimization as compared to the conventional green LEDs.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
InGaN blue light-emitting diodes (LEDs) with external quantum efficiency (EQE) exceeding 80% have been commercialized with the development of nitride material and device fabrication techniques [1]. Nevertheless, InGaN green LEDs still suffer from low emission efficiency, which is referred as the “green-gap” problem [2]. Fundamentally, the low temperature growth of the high-In InGaN well layer induces high defect density [3], and the serious quantum-confined Stark effect (QCSE) cause by the high build-in electric field significantly suppresses the radiative recombination [4]. Although carrier localization effect is demonstrated to be benefit for the alleviation of QCSE in blue InGaN LEDs [5], it is considered to introduce additional Auger recombination loss in the high-In green LEDs, and leading to the low efficiency and serious efficiency droop [6,7]. Therefore, the mentioned influences should be alleviated to improve the emission efficiency of the InGaN green LEDs.
To overcome the low efficiency of green LEDs, staggered InGaN quantum wells (QWs) [8] and hybrid multi-quantum wells (MQWs) [9] with low defect density and less QCSE are proposed. Beside the optimization on QWs structure, Okamoto et al. first proposed the surface plasmon (SP) enhanced LEDs [10], which worked on the different principle. SPs that locate at the metal-dielectric interfaces, could suppress the nonradiative recombination channels in the SP-based LEDs, they are considered to be a potential candidate to solve the efficiency droop and “green gap” problems [11,12]. Recently, researchers found that the coupling of SPs and excitons would provide a new effective path to accelerate the radiative recombination [13,14]. Cho et al. found that the exciton-SP coupling could suppress the QCSE by their excitation power-dependent PL and current-dependent EL measurements of the green LEDs with gold nanoparticles [13]. Okamoto et al. revealed that the exciton energy transfer is preferred to the SP level due to the faster energy transfer from the excitons to the SPs, thus more photons would radiate into the free space through plasmon-photon path, which would significantly reduce the QCSE and carrier localization effects [14]. To improve the internal quantum efficiency (IQE) and light extraction efficiency (LEE) of the InGaN green LEDs, propagating SP (PSP, located at the smooth interface between continuous metal layer and dielectric layer) [15–18] and localized SP (LSP) [19–25] schemes have been employed. However, there are still many difficulties in hampering the application of SPs into the InGaN green LEDs. In the case of the PSP scheme, it is difficult to modulate the SP frequency to match with the emission frequency of the InGaN active layer, which will result in lower exciton-SP coupling efficiency [12]. In addition, there is no efficient SP-photon transfer path for the PSP-based green LEDs, thus it is difficult to improve the LEE of the green LEDs. On the other hand, suitable matching conditions for the exciton-SP and SP-photon coupling can be achieved through modulating the size of the metal nanoparticles in the LSP scheme. However, nanoparticles with high density and uniform size are difficult to manufacture in InGaN-based LEDs, which reduce the exciton-SP and SP-photon coupling intensity [26].
Tamm plasmons (TPs), which could be localized between metal and distributed Bragg reflector (DBR), was first experimentally demonstrated in 2008 [27]. Adopting the TPs into the InGaN green LEDs exhibits various advantages as compared to the SP-based green LEDs. First, the eigen frequency and the half width of full maximum (FWHM) of TP mode can be conveniently modulated by adjusting the thickness of the metal film or the medium layer located between the metal film and the DBR [28]. Second, TPs are able to be excited under the metal film, and will accelerate the emission of the whole QW area, which is different from the LSPs limited by the density of nanoparticles. This property would provide sufficient IQE enhancement for the InGaN green LEDs. Third, the TPs are easily to be excited by the incident lights without additional structures such as prism or grating [29]. Thus, the employment of the TPs into the green LEDs is potential to overcome the difficulties that previously mentioned in the SP-based LEDs. Recently, enhancement of the spontaneous emission has been experimentally demonstrated in the TP-microcavity structures [30–32]. In 2017, Salewski et al. demonstrated a planar TP-microcavity structure with (In,Ga)As quantum dots (QDs), and the intensity of the optical field was amplified by more than one order of magnitude while the QD layer was located at the maximum of the electric field and close enough to the gold layer to ensure the strong coupling to the TP mode [30]. In Gubaydullin’s study, the spontaneous emission rate was increased by about one order of magnitude in TP-microcavity structure with three monolayers of InAs QDs [31]. In 2018, Morozov et al. demonstrated that the maximum registered value of the Purcell factor was close to 3 in an organic TP-microcavity structure [32]. Therefore, the TPs should be able to achieve a sufficient enhancement in the light emission efficiency for the light-emitting devices.
In this paper, we propose a TP-cavity structure with bottom DBR, medium GaN/InGaN/GaN layer and top Ag film for increasing the efficiency of InGaN-based green LEDs by the plasmon enhanced effect. Both Purcell effect and light extraction of InGaN TP-cavity LEDs were systematically investigated based on transfer matrix and 3-D finite-difference time domain (FDTD) methods. At the emission wavelength of 530 nm, the Purcell factor (Fp) and LEE of TP-cavity green LEDs were enhanced by 127% and 3.6% as compared to those of the green LEDs without top Ag film, and were enhanced by 11.2% and more than one order of magnitude than those of the green LEDs without bottom DBR, respectively. In addition, it was found that the Fp and LEE were determined by two key factors including the thicknesses of the Ag film and medium layer. Finally, the TP mode can achieve well matching with emission spectrum for optimize large enhancement by changing the thickness of the medium cavity layer easily.
2. Methodology and simulation setup
In order to analyze the TP effect on light emission performance, the transfer matrix method was employed to calculate the reflection spectra of the TP-cavity structures. A characteristic matrix of a thin-film layer can be described as follows [33]:
The total multi-layer system can be described by the matrix product of Mj (j = 1,2,3…N). The optical admittance Y of the multilayer-substrate system is calculated by the following formulas:
To investigate the light emission performance of the InGaN TP-cavity LEDs, a 3-D FDTD simulation with a coverage of 4 µm×4 µm×7 µm and perfectly-matched layer (PML) boundaries was employed. In the simulation, dipole moment was set perpendicular (parallel) to the c-axis for TE (TM) polarization. It was reported that the polarization ratio of the light emission in the InGaN-based LEDs reached 0.9 in general [34](corresponding to a ratio of 19:1 for TE/TM polarization). Thus, only the TE polarization was used in this simulation. It should be noted that both the s-polarization and p-polarization light can be emitted by the TE polarization dipoles in the InGaN-based LEDs. The schematic structure of the InGaN TP-cavity LEDs (named as sample A) is shown in Fig. 1(a). The TP-cavity structure is composed of a 30 nm-thick Ag film (the complex permittivity data are taken from Johnson and Christy [35]), 142 nm-thick medium GaN/InGaN/GaN layer, 35.5 pairs of AlN/GaN nitride DBR (with thickness dAlN=69.23 nm and dGaN=56.25 nm, refractive index nAlN=1.95 and nGaN=2.40, the imaginary parts could be neglected at the emission region. The bottom and top layers of DBR are both AlN layers). The DBR with λ/4 optical thickness for each layer supports a stopband with a center wavelength of 540 nm and a bandwidth of 75 nm. The nitride DBR is widely used in electrically injected GaN-based light-emitting devices for its electrical conductivity. The electric dipole source polarized in the in-plane direction is located at the center of 2 nm-thick InGaN well layer (with refractive index of 2.55). InGaN-based LEDs without top Ag film (denoted as sample B) or without bottom nitride DBR (denoted as sample C) for comparative study were shown in Figs. 1(b) and 1(c), respectively. The corresponding layers are the same in the three samples. The spontaneous emission enhancement rate can be evaluated from Purcell factor, which is calculated by the ratio of dipole emission power in the device to the bulk material. While the Fp is higher than 1, the radiative recombination process is accelerated and the IQE of the LEDs would be increased. A frequency-domain field and power monitor was fixed at 500 nm over the structure to record the power radiated upward Pup, and a box with the size of 50nm×50nm×50 nm was surrounded the dipole to record the radiative power Prad. Then, the LEE of the LEDs is calculated by Pup/ Prad. In this simulation, the PML boundary was used to minimize the size of the device, and the lateral emission and reflection of the light from the edge of the devices are neglected.
Fig. 1. Schematic structures of the InGaN-based LEDs (a) with TP-cavity structure (sample A), (b) without top Ag film (sample B) and (c) without bottom DBR (sample C).
3. Results and discussion
3.1 Purcell effect and light extraction of the InGaN TP-cavity LEDs
Figures 2(a) and 2(b) show the Fp and LEE of InGaN-based LEDs using the FDTD simulation method. It is found that the Fp of the sample B is around 1 in the simulated wavelength range of 400 nm to 700 nm. In contrast with sample B, sample A and sample C possess a larger Fp, which would be benefit to achieve a higher IQE for the InGaN green LEDs. And, the value of Fp is more than 2 for sample A and sample C from the wavelength of 450 to 550 nm, which is attributed to the presence of the TP and/or SP modes that induced by the DBR and/or top Ag film. This part will subsequently be discussed in detail. It is also found that the maximum Fp of the sample C is 2.29 at 480 nm. The PSP resonance wavelength, which is mainly determined by permittivity of metal ${\varepsilon _m}$ and the dielectric material ${\varepsilon _d}$, should be located at 430 nm for Ag and GaN interface according to the theoretical calculation [12]. Although there is no grating or prism structure, PSP can also be excited in the case of near-field coupling. The dipole is 31 nm below the Ag film, which is also in the evanescent field of the PSP. The emitted lights are coupled to the evanescent field and PSP is excited. However, the short wavelength region of PSP mode (lower than 480 nm) corresponds to a shorter evanescent field distance, which reduces the near-field couple efficiency. It leads to a red shift of maxima Fp to 480 nm as shown in Fig. 2(a). The near-field patterns in Figs. 3(c) and 3(d) clearly exhibit that PSP modes propagating along the Ag film are both excited in sample A and sample C. As the dipole is located in the evanescent-field, it has been widely reported that the emission rate will be accelerated by the strong electromagnetic field, resulting in a higher Purcell factor. As compared to sample C, the typical top radiation behavior without rapid decay was observed for sample A due to the existence of TP mode, which will be discussed later. In Fig. 2(a), it is also found that the Fp of sample A (2.38) was enhanced by 127% and 11.2% as compared to that of sample B (1.05) and sample C (2.14) at the emission wavelength of 530 nm. For the InGaN TP-cavity LEDs, the enhanced Fp value was the consequence of both the SP and TP effects, which indicated that the TP effect helped to further accelerate the spontaneous emission process. The sudden decline at the wavelength of 540 nm for the sample A can be understood by the angle dependent reflection spectra as shown in Fig. 3(a). The angle dependent reflection spectra with s and p-polarization were calculated by the transfer matrix method. It shows a blue shift of TP mode as the incident angle increases from 0 to 45 degree, and the calculated TP mode matches well to the results simulated by the FDTD method (pink dot-line in Fig. 3(a)). The longest wavelengths of the TP mode for both s and p-polarization are located at 540 nm while the incident angle is zero degree. At the emission wavelength of around 540 nm, the Purcell actor rapidly decreases as shown in Fig. 2(a), which is another powerful evidence that the enhanced Purcell effect is attributed to the existence of TPs in the sample A.
Fig. 3. (a) Reflection spectra of the TP-cavity LEDs calculated by transfer matrix method with s and p-polarization at different incidence angles. The pink dot-line is peak positions of the TP mode simulated by FDTD method, the colorbar at right represents the reflectivity. (b) Far-field patterns of light emission intensity in sample A. Near-field pattern at 540 nm of (c) sample A (d) sample C. The colorbars in Figs. 3(c) and 3(d) represent electric field in log scale, which is normalized by the electric field of dipole source in bulk material. The red lines are the location of InGaN layer, and the white lines are the boundaries of different materials.
It can be found in Fig. 2(b) that the LEE of the sample C is around 1.0% in the simulated wavelength range of 400 nm to 700 nm, and the LEE of the sample A and sample B are an order of magnitude higher than that of sample C from the emission wavelength of 490 nm to 540 nm. The lower LEE of the sample C was caused by the top 30-nm thick Ag film in which the emitted photons would be absorbed or reflected. The LEE of the sample A rapidly decreases when the emission wavelength is higher than 540 nm which is still at the stopband of the bottom DBRs. It indicates the LEE enhancement in sample A should not only be attributed to the light reflection effect of the bottom DBR. It is also found that the LEE of TP-cavity LED is even higher than that of the sample B at the wavelength range of 525 nm to 535 nm, despite the existent absorption loss in the Ag film. These results mean that the TP effect can offer an efficient path for light extraction and increase the light emission. The light extraction is strongly relying on the TP effect, which could be further proved by the far-field patterns as shown in Fig. 3(b). While the emission wavelength is shorter than 540 nm, the blue shift of the TP mode corresponds to a larger extraction angle, revealing the same tendency as the reflectivity spectra shown in Fig. 3(a). At the normal excited TP mode at λ=540 nm, the emission intensity of TP-cavity LEDs is the highest as seen from the far-field pattern. The near-field patterns in Figs. 3(c) and 3(d) also demonstrate the radiation behavior. It is found that the radiation intensity of sample A is much stronger than that of sample C along the z-axis. This is due to the TP effect produced in the sample A, which supports an efficient path for the photons to escape. For λ=545 nm (orange line), which is still located at the right edge of the 540 nm TP mode as shown in Fig. 3(a), thus TP-cavity LEDs still have a certain emission intensity. However, for longer wavelength (such as 550 nm) which is out of the TP mode, the intensity radically decreases.
3.2 Effect of the top Ag film on the Fp and LEE of the InGaN TP-cavity LEDs
It is known that the thickness of top Ag film has a significant influence on the TP effect [36], thus it is quite important to investigate the effect of the top Ag film on the emission of the InGaN TP-cavity LEDs. Figure 4(a) shows the reflection spectra of the TP-cavity LEDs calculated by the transfer matrix method as function of the thickness of the Ag film. The TP mode is obviously observed as the thickness of the Ag film is larger than 5 nm. As the top Ag layer is thicker than 40 nm, the wavelength of the TP modes becomes steady, at the meantime, the reflectivity becomes lower and the linewidth becomes narrower. The wavelength movement of the TP modes is mainly ascribed to the change of the penetration depth of the Ag layer. The frequency of the TP mode and the penetration depth of the Ag layer can be descripted by the following equation [37]:
Fig. 4. (a) Reflection spectra of the InGaN TP-cavity LEDs calculated by the transfer matrix method as function of the thickness of the top Ag film. The colorbar represents the reflectivity of the TP-cavity structure. (b) Fp and (c) LEE of the TP-cavity LEDs simulated by FDTD method as the Ag film thickness changed from 10 to 50 nm.
Where ω is the angular frequency of TP mode and ω0 is the center angular frequency of DBR. The parameters ncav and Lcav are refractive index and length of the cavity between DBR and metal film, respectively. The parameters nDBR and LDBR are the effective refractive index and penetration depth of the DBR, respectively. The parameters nm and Lm are the refractive index and penetration depth of metal film, respectively. And c is the light speed in vacuum, N (=1, 2, 3…) is denoted as mode number. In a thin Ag film (<40 nm), the effect of multibeam interference cannot be ignored, which leads to the change of reflection phase shift and results in a larger penetration depth with the decrease of Ag film thickness. The details are discuss in [37,38]. While decreasing the thickness of Ag film, the penetration depth grows rapidly and results in longer effective cavity length, thus leads to a red shift of the TP mode as shown in Fig. 4(a). When the thickness increases thicker than 40 nm, the penetration depth remains unchanged and the phase matching condition does not change, thus the wavelength of the TP mode becomes steady. It’s also notable that when the metal is relatively thin, resulting in a large linewidth and low quality factor, which is caused by the weak confinement and large leakage. On the contrary, the linewidth is very narrow while the Ag film is thick enough.
Figures 4(b) and 4(c) show the Fp and LEE of the TP- cavity LED simulated by FDTD method as the thickness of the Ag film changed from 10 to 50 nm, respectively. As the thickness of the Ag film increases, the Fp is gradually increased and then steady at a high value. Thus, a weak TP mode limited by a thin metal thickness cannot support an effective enhancement. Although the considerable decrease of the LEE is caused by the larger absorption loss in the thicker Ag film. It is also noted that asymmetry of the LEE curve gradually grows as the thickness of the Ag film increases, which was due to the existence of the TP effects. When excluding the influence of TP and SP effect, the absorption of Ag film would show no obvious difference at different wavelength. However, LEE of the TP-cavity LEDs exhibits a steep rise for TP mode at the normal direction due to the strong TP effect caused by the thicker Ag film, slowing down the decline and resulting in the asymmetry of LEE curve. Therefore, an appropriate thickness of the metal film should be applied to maintain a high Fp and LEE value, lowering the unexpected absorption loss.
3.3 Effect of the medium layer on the Fp and LEE of InGaN TP-cavity LEDs
Figure 5(a) shows the medium layer thickness dependent reflection spectra of the TP-cavity LEDs calculated by the transfer matrix method. As the thickness of the medium layer increases, the peak wavelength of the TP mode exhibits an almost periodical shift in the stopband of the DBR. The results indicate a high overlap between TP modes and the emission spectra can be achieved by controlling the thickness of the medium layer, and the spontaneous emission rate would be highly accelerated. The thickness of the medium layer is changed by controlling the thickness of the top GaN layer (located between the InGaN layer and the Ag film) in the simulations. Thus, the distance between InGaN layer and DBR keeps constant in sample A. For the light with emission wavelength of 540 nm, it travels along z-axis and the phase distribution is highly determined by the DBR (i.e. the antinodes and nodes are located at the AlN/GaN interfaces in the DBR), and the first antinode in medium layer are set to be located at the dipole source. So, when the TP mode is excited at 540 nm, the emission will be enhanced. Figures 5(b) and 5(c) show the Fp and LEE of the TP-cavity LEDs as function of the thickness of the medium layer, respectively. Three interesting regular patterns are revealed both in the Fp and LEE mapping images. The bright oblique zigzag lines formed at the right position of the patterns are corresponding to the excited TP modes at the normal direction. It is found that the size of the patterns formed in the LEE mapping image is much smaller than that in the Fp mapping image. This is caused by the large absorption in the metal layer located around antinode of the electric field when the wavelength of the emitted photons is outside of the TP mode region. In addition, the photons with short-wavelength are more difficult to escape due to the larger escaped angle, thus resulting in low LEE. It is also noted that the Fp values are significantly larger while the medium layer is very thin, which is similar to the results of Ryu’s report [39]. The TP-cavity structure with short cavity would have high spontaneous emission enhancement due to the strong electric field confinement. In addition, it is noteworthy that Purcell enhancement is also observed at the wavelength shorter than 500 nm (out of the stopband of the DBR), which should be attributed to the mixture of the SP modes. Although a high Fp value could benefit from these SP modes, however, it is difficult to realize high LEE due to the large absorption. The reason is that no effective plasmon-photon path exists for light to escape, the photons are mainly transferred into thermal loss. Therefore, an appropriate medium layer is important to be taken into account for the balance between the LEE and the Fp in the design of the TP-cavity LEDs.
Fig. 5. Medium layer thickness dependent (a) reflection spectra of the TP-cavity LEDs calculated by transfer matrix method. (b) Fp and (c) LEE of the TP-cavity LEDs as function of the thickness of the medium layer. 8 nm step length of the medium layer is adopted. The zigzag patterns are caused by the limited simulation step length. The colorbars in Figs. 5(a)–5(c) represent the value of the reflectivity, FP and LEE, respectively.
3.4 Emission performance enhancement of the InGaN green LEDs by utilizing the TP-cavity structure
An effective enhancement requires well matching between the TP mode and emission spectrum of the QWs in TP-cavity green LEDs. Thus, two normalized electroluminescence (EL) spectra of InGaN green LED chip in our previous report [40] with different peak wavelength (540 nm and 530 nm, denoted as EL-A and EL-B) as shown in Fig. 6(a), are applied to investigate the emission performance of the TP-cavity green LEDs. These spectra describe emission intensity-wavelength relationship of InGaN QWs, which were taken into our theoretical calculation as IEL in Eq. (8), for considering the intensity weight on the emission wavelength. Then, the emission intensity of the TP-cavity green LEDs (I) can be calculated by following equation:
Fig. 6. (a) Normalized EL spectra of green LEDs with peak wavelength of 540 nm (EL-A) and 530 nm (EL-B). (b) Medium layer thickness dependent integrated emission intensity of the TP- cavity green LEDs and the normal green LEDs.
Where ηEQE is the external quantum efficiency of the green LED chip in [40], η’LEE is LEE of the TP-cavity green LEDs shown in Fig. 5(c). The IQE of the TP-cavity green LEDs (η’IQE) could be calculated by the following equation [39]:
4. Summary
In summary, we have proposed the TP-cavity hybrid structure with bottom DBR, medium GaN/InGaN/GaN layer and top Ag film to improve the light emission efficiency of the InGaN LEDs. The Purcell effect and light extraction are strongly relying on the presence of the TP and/or SP modes. The significant advantage for the utilization of the TPs is that the remarkable enhancement of the light emission could be easily achieved by selecting the suitable metal film and adjusting the thickness of the medium layer. Finally, the light emission intensity was greatly enhanced for the TP-cavity green LEDs after the structure optimization, and the results indicate that the properly designed TP-cavity structure is very effective to improve the emission of the green LEDs in a large injection current range. Therefore, introduce of the TPs into the InGaN green LEDs would be able to overcome the difficulties in solving the efficiency droop and “green gap” problems, resulting in high emission efficiency. Our studies could offer theoretical guidance for device design of the TP-cavity LEDs.
Funding
National Natural Science Foundation of China (61604179, 61975037); Science and the Technology Project of Guangzhou City (201707010067); Fundamental Research Funds for the Central Universities (2018ZD44).
References
1. Y. Narukawa, M. Ichikawa, D. Sanga, M. Sano, and T. Mukai, “White light emitting diodes with super-high luminous efficacy,” J. Phys. D: Appl. Phys. 43(35), 354002 (2010). [CrossRef]
2. P. Dawson, M. J. Davies, C. J. Humphreys, M. A. Hopkins, R. A. Oliver, T. Williams, S. K. Pamenter, R. E. Dunin-Borkowski, D. W. E. Allsopp, F. C.-P. Massabuau, J. Etheridge, M. J. Kappers, F. Oehler, A. Kovács, and E. J. Thrush, “The impact of trench defects in InGaN/GaN light emitting diodes and implications for the “green gap” problem,” Appl. Phys. Lett. 105(11), 112110 (2014). [CrossRef]
3. S. Hammersley, M. J. Kappers, F. C. P. Massabuau, S. L. Sahonta, P. Dawson, R. A. Oliver, and C. J. Humphreys, “Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions,” Appl. Phys. Lett. 107(13), 132106 (2015). [CrossRef]
4. S. De, A. Layek, S. Bhattacharya, D. Kumar Das, A. Kadir, A. Bhattacharya, S. Dhar, and A. Chowdhury, “Quantum-confined stark effect in localized luminescent centers within InGaN/GaN quantum-well based light emitting diodes,” Appl. Phys. Lett. 101(12), 121919 (2012). [CrossRef]
5. S. Zhu, S. Lin, J. Li, Z. Yu, H. Cao, C. Yang, J. Li, and L. Zhao, “Influence of quantum confined Stark effect and carrier localization effect on modulation bandwidth for GaN-based LEDs,” Appl. Phys. Lett. 111(17), 171105 (2017). [CrossRef]
6. Y. C. Leem and S. Y. Yim, “Microscopic Observation of Low Efficiency in Green Light-Emitting Diodes,” ACS Photonics 5(3), 1129–1136 (2018). [CrossRef]
7. C. M. Jones, C. H. Teng, Q. Yan, P. C. Ku, and E. Kioupakis, “Impact of carrier localization on recombination in InGaN quantum wells and the efficiency of nitride light-emitting diodes: Insights from theory and numerical simulations,” Appl. Phys. Lett. 111(11), 113501 (2017). [CrossRef]
8. H. Zhao, G. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, and N. Tansu, “Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells,” Opt. Express 19(S4), A991 (2011). [CrossRef]
9. Y. Jiang, Y. Li, Y. Li, Z. Deng, T. Lu, Z. Ma, P. Zuo, L. Dai, L. Wang, H. Jia, W. Wang, J. Zhou, W. Liu, and H. Chen, “Realization of high-luminous-efficiency InGaN light-emitting diodes in the “green gap” range,” Sci. Rep. 5(1), 10883 (2015). [CrossRef]
10. K. Okamoto, I. Niki, A. Shvartser, Y. Narukawa, T. Mukai, and A. Scherer, “Surface-plasmon-enhanced light emitters based on InGaN quantum wells,” Nat. Mater. 3(9), 601–605 (2004). [CrossRef]
11. I.-H. Lee, L.-W. Jang, and A. Y. Polyakov, “Performance enhancement of GaN-based light emitting diodes by the interaction with localized surface plasmons,” Nano Energy 13, 140–173 (2015). [CrossRef]
12. K. Okamoto, M. Funato, Y. Kawakami, and K. Tamada, “High-efficiency light emission by means of exciton–surface-plasmon coupling,” J. Photochem. Photobiol., C 32, 58–77 (2017). [CrossRef]
13. C.-Y. Cho and S.-J. Park, “Enhanced optical output and reduction of the quantum-confined Stark effect in surface plasmon-enhanced green light-emitting diodes with gold nanoparticles,” Opt. Express 24(7), 7488 (2016). [CrossRef]
14. K. Tateishi, P. Wang, S. Ryuzaki, M. Funato, Y. Kawakami, K. Okamoto, and K. Tamada, “Micro-photoluminescence mapping of surface plasmon enhanced light emissions from InGaN/GaN quantum wells,” Appl. Phys. Lett. 111(17), 172105 (2017). [CrossRef]
15. H. Zhao, J. Zhang, G. Liu, and N. Tansu, “Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light-emitting diodes,” Appl. Phys. Lett. 98(15), 151115 (2011). [CrossRef]
16. H. Zhang, J. Zhu, Z. Zhu, Y. Jin, Q. Li, and G. Jin, “Surface-plasmon-enhanced GaN-LED based on a multilayered M-shaped nano-grating,” Opt. Express 21(11), 13492–13501 (2013). [CrossRef]
17. Y.-W. Kiang, Y.-F. Yao, W.-Y. Chang, C.-Y. Su, C.-H. Lin, C.-Y. Chao, C. C. Yang, and C.-G. Tu, “Coupling of a light-emitting diode with surface plasmon polariton or localized surface plasmon induced on surface silver gratings of different geometries,” Opt. Express 26(7), 9205 (2018). [CrossRef]
18. G. Zhang, X. Guo, F. Ren, Y. Li, B. Liu, J. Ye, H. Ge, Z. Xie, R. Zhang, H. H. Tan, and C. Jagadish, “High-Brightness Polarized Green InGaN / GaN Light-Emitting Diode Structure with Al-Coated p-GaN Grating,” ACS Photonics 3(10), 1912–1918 (2016). [CrossRef]
19. D. M. Yeh, C. F. Huang, C. Y. Chen, Y. C. Lu, and C. C. Yang, “Localized surface plasmon-induced emission enhancement of a green light-emitting diode,” Nanotechnology 19(34), 345201 (2008). [CrossRef]
20. C. Y. Cho, S. J. Lee, J. H. Song, S. H. Hong, S. M. Lee, Y. H. Cho, and S. J. Park, “Enhanced optical output power of green light-emitting diodes by surface plasmon of gold nanoparticles,” Appl. Phys. Lett. 98(5), 051106 (2011). [CrossRef]
21. J. Xing, Y. Chen, Y. Liu, J. Liang, J. Chen, Y. Ren, X. Han, C. Zhong, H. Yang, D. Huang, Y. Hou, Z. Wu, Y. Liu, and B. Zhang, “Enhancement of emission of InGaN/GaN multiple-quantum-well nanorods by coupling to Au-nanoparticle plasmons,” J. Appl. Phys. 123(19), 193101 (2018). [CrossRef]
22. J. Li, P. Gou, N. Chi, and H. Ou, “Enhanced Emission and Modulation Properties of Localized Surface Plasma Coupled GaN-based Green Light-Emitting Diodes,” in Optical Fiber Communication Conference (OSA, 2018), (c), paper Th2A.65.
23. A. Fadil, Y. Ou, D. Iida, S. Kamiyama, P. M. Petersen, and H. Ou, “Combining surface plasmonic and light extraction enhancement on InGaN quantum-well light-emitters,” Nanoscale 8(36), 16340–16348 (2016). [CrossRef]
24. M. Kwon, J. Kim, B. Kim, I. Park, C. Cho, C. C. Byeon, and S. Park, “Surface-Plasmon-Enhanced Light-Emitting Diodes,” Adv. Mater. 20(7), 1253–1257 (2008). [CrossRef]
25. Z.-G. Yu, L.-X. Zhao, X.-C. Wei, X.-J. Sun, P.-B. An, S.-C. Zhu, L. Liu, L.-X. Tian, F. Zhang, H.-X. Lu, J.-X. Wang, Y.-P. Zeng, and J.-M. Li, “Surface plasmon-enhanced nanoporous GaN-based green light-emitting diodes with Al2O3 passivation layer,” Opt. Express 22(S6), A1596 (2014). [CrossRef]
26. S.-C. Zhu, Z.-G. Yu, L.-X. Zhao, J.-X. Wang, and J.-M. Li, “Enhancement of the modulation bandwidth for GaN-based light-emitting diode by surface plasmons,” Opt. Express 23(11), 13752 (2015). [CrossRef]
27. M. E. Sasin, R. P. Seisyan, M. A. Kalitteevski, S. Brand, R. A. Abram, J. M. Chamberlain, A. Y. Egorov, A. P. Vasil’Ev, V. S. Mikhrin, and A. V. Kavokin, “Tamm plasmon polaritons: Slow and spatially compact light,” Appl. Phys. Lett. 92(25), 251112 (2008). [CrossRef]
28. H. Zhou, G. Yang, K. Wang, H. Long, and P. Lu, “Multiple optical Tamm states at a metal-dielectric mirror interface,” Opt. Lett. 35(24), 4112–4114 (2010). [CrossRef]
29. T. Goto, A. V. Dorofeenko, A. M. Merzlikin, A. V. Baryshev, A. P. Vinogradov, M. Inoue, A. A. Lisyansky, and A. B. Granovsky, “Optical Tamm states in one-dimensional magnetophotonic structures,” Phys. Rev. Lett. 101(11), 113902 (2008). [CrossRef]
30. M. Salewski, S. V. Poltavtsev, Y. V. Kapitonov, J. Vondran, D. R. Yakovlev, C. Schneider, M. Kamp, S. Höfling, R. Oulton, I. A. Akimov, A. V. Kavokin, and M. Bayer, “Photon echoes from (In,Ga)As quantum dots embedded in a Tamm-plasmon microcavity,” Phys. Rev. B 95(3), 035312 (2017). [CrossRef]
31. A. R. Gubaydullin, C. Symonds, J. Bellessa, K. A. Ivanov, E. D. Kolykhalova, M. E. Sasin, A. Lemaitre, P. Senellart, G. Pozina, and M. A. Kaliteevski, “Enhancement of spontaneous emission in Tamm plasmon structures,” Sci. Rep. 7(1), 9014 (2017). [CrossRef]
32. K. M. Morozov, K. A. Ivanov, N. Selenin, S. Mikhrin, D. de Sa Pereira, C. Menelaou, A. P. Monkman, and M. A. Kaliteevski, “Purcell effect investigation in organic Tamm plasmon structures,” J. Phys.: Conf. Ser. 1135, 012082 (2018). [CrossRef]
33. B. E. Perilloux, Thin-Film Design: Modulated Thickness and Other Stopband Design Methods (SPIE, 2002).
34. H. Masui, N. N. Fellows, S. Nakamura, and S. P. DenBaars, “Optical polarization characteristics of light emission from sidewalls of primary-color light-emitting diodes,” Semicond. Sci. Technol. 23(7), 072001 (2008). [CrossRef]
35. P. B. Johnson and R. W. Christy, “Optical constants of the noble metals,” Phys. Rev. B 6(12), 4370–4379 (1972). [CrossRef]
36. M. Kaliteevski, I. Iorsh, S. Brand, R. A. Abram, J. M. Chamberlain, A. V. Kavokin, and I. A. Shelykh, “Tamm plasmon-polaritons: Possible electromagnetic states at the interface of a metal and a dielectric Bragg mirror,” Phys. Rev. B 76(16), 165415 (2007). [CrossRef]
37. M. Adams, B. Cemlyn, I. Henning, M. Parker, E. Harbord, and R. Oulton, “Model for confined Tamm plasmon devices,” J. Opt. Soc. Am. B 36(1), 125 (2019). [CrossRef]
38. F. Ma and X. Liu, “Phase shift and penetration depth of metal mirrors in a microcavity structure,” Appl. Opt. 46(25), 6247–8250 (2007). [CrossRef]
39. H.-Y. Ryu, “Modification of internal quantum efficiency and efficiency droop in GaN-based flip-chip light-emitting diodes via the Purcell effect,” Opt. Express 23(19), A1157 (2015). [CrossRef]
40. X. Hu, F. Xiao, Q. Zhou, Y. Zheng, and W. Liu, “High-luminous efficacy green light-emitting diodes with InGaN/GaN quasi-superlattice interlayer and Al-doped indium tin oxide film,” J. Alloys Compd. 794, 137–143 (2019). [CrossRef]
41. M. A. der Maur, A. Pecchia, G. Penazzi, W. Rodrigues, and A. Di Carlo, “Efficiency Drop in Green InGaN/GaN Light Emitting Diodes: The Role of Random Alloy Fluctuations,” Phys. Rev. Lett. 116(2), 027401 (2016). [CrossRef]
