Dr. Juemin Yi Profile

Dr. Juemin Yi

at SINANO CAS

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Publications (2)

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Proceedings Article | 4 April 2023 Paper

Effect of intermediate states on optical nonlinearities in Fe-doped GaN single crystals

Ye Song, Minxue Wang, Juemin Yi, Yumin Zhang, Jianfeng Wang, YingLin Song, Bing Cao, Ke Xu

Proceedings Volume 12617, 126177D (2023) https://doi.org/10.1117/12.2666834

KEYWORDS: Gallium nitride, Iron, Absorption, Crystals, Ultrafast phenomena, Refraction, Doping, Nonlinear optics, Technology, Carrier dynamics

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Semiconductor doping strongly influences its electrical and optical properties. The transition metal Fe doping can induce the deep levels to compensate residual donors to generate semi-insulating GaN, and make carrier lifetime short due to carrier trapping, which thus has potential applications in ultrafast optical and optoelectronic devices. For such applications, it is critical to understand the effect of Fe doping on optical nonlinearities and ultrafast carrier dynamics in GaN crystals. In this paper, we studied the dependence of GaN ultrafast nonlinearities on Fe-related intermediate states using femtosecond two-photon Z-scan and pump-probe with phase object (PO) techniques. In particular, we investigated the nonlinearities around 458 nm (2.71 eV) and 540 nm (2.29 eV) where it shows dips in transmission spectra. It is found that the two-photon absorption coefficient has a minimum value at the peak of 458 nm, in contrast, the coefficient has a maximum value at the peak of 540 nm and enhances around 1.5 times more. It thus indicates that these two absorption resonances are attributed to different physical reasons. We further investigated the ultrafast carrier dynamics by the time-resolved PO pump-probe techniques with 190 fs laser pulses. We observed that the transient refraction curves are recovered once pump and probe pulses are separated in time delay. It is considered that carrier lifetime is dramatically reduced due to Fe trapping centers. Our finding that Fe-doped semi-insulating GaN has ultrafast carrier lifetime expect GaN potential applications in ultrafast detectors and all-optical switches.

Proceedings Article | 9 October 2021 Poster + Paper

All-dielectric nanostructures for high-efficient angular emission from polarized LEDs

Miao Wang, Juemin Yi, Yumin Zhang, Bing Cao, Chinhua Wang, Jianfeng Wang, Ke Xu

Proceedings Volume 11894, 1189417 (2021) https://doi.org/10.1117/12.2602690

KEYWORDS: Light emitting diodes, Nanostructures, Dielectrics, Gallium nitride, Collimation, Flat panel displays, Radiation effects

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Gallium nitride (GaN) -based light-emitting diodes (LEDs) have been widely used in lighting, display, communication and other fields due to their high brightness, high luminous efficiency and low power consumption. Polarized LEDs have important potential application in flat panel display, holographic display and imaging fields. It’s very important to study how to realize efficient polarized LEDs. Realizing directional radiation (collimation) is one of the effective methods to improve the utilization efficiency of polarized light. In this paper, we proposed an all-dielectric (Al2O3/SiO2) films/(TiO2) grating nanostructures, and found that the enhanced emission of the polarized LED can be controlled within a specific angle by optimizing the parameters of the all-dielectric nanostructures. In particular, the simulation results show that the angular emission of polarized blue LEDs can be controlled within 11°, and the light output efficiency is more than 60% when the nanostructure is set as: Al2O3/SiO2 film thickness 70 nm, grating period 500 nm, line width 180 nm, and depth 100 nm. The peak light intensity is 5.2 times that of the bare LED. This nanostructure can be prepared easily and it has a large process tolerance. Our findings will provide the feasibility for achieving efficient polarized LEDs in display technology and imaging fields.

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