Browsing by Author "Long, Hanling"

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Bio-Inspired Flexible Fluoropolymer Film for All-Mode Light Extraction Enhancement
(2019-05-29)
Liang, Renli
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Hu, Run
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Long, Hanling
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Huang, Xinyu
;
Dai, Jiangnan
Enhancing the light extraction efficiency is a prevalent but vital challenge for most solid-state lighting technologies, especially for deep ultraviolet light-emitting diodes (DUV-LEDs). In this paper, inspired by the micro-structure of the butterfly's eye, we propose and fabricate a flexible fluoropolymer film (FFP film) to tackle this issue for all-mode, full-wavelength light extraction enhancement for most solid-state lighting technologies compatibly. The experimental results demonstrate that compared with one mounted with a smooth FFP film, the light output power of DUV-LED is enhanced up to 26.7% by mounting the FFP film with 325 nm radius nanocones at a driving current of 200 mA. Importantly, thanks to the super-flexible feature of the FFP film, it can both cover the top surface and sidewalls of the DUV-LED chip, leading to the improvement of transverse electric and transverse magnetic mode light extraction by 20.5 and 21.8%, respectively. Finite element analysis (FEA) simulations of the electric field distribution of DUV-LEDs with the FFP film reveal the underlying physics. The present strategy is proposed from the view of the packaging level, which is cost-effective, able to be manufactured at a large scale, and compatible with the solid-state lighting technologies.
Enhanced Optical Performance of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Electrode Patterns Design
(2019-12-01)
Chen, Qian
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Dai, Jiangnan
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Li, Xiaohang
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Gao, Yang
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Long, Hanling
Low external quantum efficiency of deep ultraviolet light-emitting diodes (DUV LEDs) and current crowding can result in considerable heat generation, which has a great negative impact on device performance. In this paper, we investigate the influence of different electrode patterns on the photoelectric and thermal performance of DUV LEDs. We find that different electrode designs can achieve drastically different optical powers, with the superior design being the n-type electrode surrounding the active region. Moreover, compared with the counterpart, the superior design does not affect the electrical performance. The main reason is that the N-surrounding electrode pattern can provide enough current paths for carrier transport, thus realizing a more uniform current injection and can further improve the external quantum efficiency for DUV LEDs.
High quality 10.6 mu m AIN grown on pyramidal patterned sapphire substrate by MOCVD
(2019-01-28)
Long, Hanling
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Dai, Jiangnan
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Zhang, Yi
;
Wang, Shuai
;
Tan, Bo
In this letter, we demonstrate a crack and strain free AlN epilayer with a thickness of 10.6 mu m grown on a pyramidal patterned sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of the X-ray rocking curve was 165/185 arcsec for (002)/(102) planes, respectively. The total threading dislocation density was less than 3 x 10(8) cm(-2). The dislocation evolution and the coalescence process were probed by transmission electron microscopy and scanning electron microscopy. A dual coalescence of the AlN epilayer was observed, which can effectively relax strain during the heteroepitaxy process. Owing to the approximately entire strain relaxation demonstrated by reciprocal space mapping and Raman shift, the surface morphology was crack-free and atomically smooth with a root-mean-square roughness of 0.14 nm. Temperature dependent Raman spectra showed the Raman linewidth of 4.3 cm(-1) at 300 K which was comparable to that of bulk AlN; it also demonstrated good crystalline quality of the AlN epilayer. Published under license by AIP Publishing.
Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure
(2018-09-01)
Wang, Shuai
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Dai, Jiangnan
;
Hu, Jiahui
;
Zhang, Shuang
;
Xu, Linlin
For the first time, an ultrahigh degree of optical polarization (DOP) of 81.8% in AlGaN-based deep ultraviolet LED (DUV-LED) operated at 286 nm has been experimentally demonstrated. The very high DOP was obtained by introducing the novel moth-eye microstructure fabricated on the backside of a sapphire substrate. Compared with conventional DUV-LED with a DOP of 64.7%, a significant 1.26-fold enhancement was obtained. It was worth mentioning that the DOP was accurately measured via self-built full spatial transverse electric (TE) and transverse magnetic (TM) mode light intensity test system, which was mainly composed of angle resolution bracket, Glan-Taylor prism, and spectrometer. For both TE and TM mode light, the extraction angle inside the semiconductor was extended from conventional (-26 degrees, 26 degrees), (-52 degrees, -41 degrees), (41 degrees, 52 degrees) to (-52 degrees, 52 degrees). Combined with finite difference time domain simulation, it was further confirmed that the novel moth-eye microstructure could notably weaken the total internal reflection at the sapphire/air interface and enlarge the light extraction angle. As a result, compared with the conventional one, DUV-LED with a moth-eye microstructure approximately doubled the light extraction efficiency.
Ultraviolet polarized light emitting and detecting dual-functioning device based on nonpolar n-ZnO/i-ZnO/p-AlGaN heterojunction
(2019-04-15)
Dai, Jiangnan
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Chen, Jingwen
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Li, Xiaohang
;
Zhang, Jun
;
Long, Hanling
We report on the demonstration of a 386 nm light emission and detection dual-functioning device based on nonpolar a-plane n-ZnO/i-ZnO/p-Al0.1Ga0.9N heterojunction under both forward and reverse bias. The electroluminescence intensity under reverse bias is significantly stronger than that under forward bias, facilitated by carrier tunneling when the valence band of p-AlGaN aligns with the conduction band of i-ZnO under reverse bias. Also amid reverse bias, the photodetection was observed and applied in a duplex optical communication device. Optical polarization of the light emission is studied for potential polarization-sensitive device applications. The proposed device provides an important pathway for the multifunctional devices operating in a UV spectrum. (C) 2019 Optical Society of America