| 1. |
- Nie, Junyang, et al.
(author)
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Systematic study on size and temporal dependence of micro-LED arrays for display applications
- 2023
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In: Photonics Research. - 2327-9125. ; 11:4, s. 549-557
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Journal article (peer-reviewed)abstract
- Micro-LEDs are one of the most promising candidates for next-generation displays, yet they are inconvenienced by the efficiency reduction induced by the sidewall defects when pursuing further scaled-down device dimensions. We have systematically investigated both the size and temporal dependence of micro-LEDs. Micro-LED arrays with a mesa size ranging from 7 to 100 μm were prepared for display purposes. The luminance and external quantum efficiency (EQE) were measured and discussed. Surprisingly, micro-LED arrays with a smaller mesa size exhibit a higher EQE under 100 ns pulse duration operation when compared with longer pulse duration operations. Under certain short-pulsed excitation, a 7 × 7 μm2 micro-LED array even exhibits a >20% higher EQE as compared to the direct current (DC) or the long duration pulse operation condition.We thus concluded that the notorious efficiency reduction induced by sidewall defects in small-sized micro-LED arrays could be significantly reduced by applying short-pulse voltages.
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| 2. |
- Pan, Kui, et al.
(author)
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Highly effective transfer of micro-LED pixels to the intermediate and rigid substrate with weak and tunable adhesion by thiol modification
- 2023
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 15:9, s. 4420-4428
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Journal article (peer-reviewed)abstract
- Based on transfer printing technology, micro-LED pixels can be transferred to different types and sizes of driving substrates to realize displays with different application scenarios. To achieve a successful transfer, GaN-based micro-LEDs first need to be separated from the original epitaxial substrate. Here, micro-LED pixels (each size 25 μm × 30 μm) on the sapphire substrate were transferred to a flexible semiconductor wafer processing (SWP) tape that is strongly sticky by conventional laser lift-off (LLO) techniques. The pixels on the SWP tape were then transferred by using a sacrificial layer of non-crosslinked oligomeric polystyrene (PS) film onto the intermediate and rigid substrate (IRS) with weak and tunable adhesion by thiol (-SH) modification. The electrode of the micro-LED is Au metal, which forms Au-S bonds with the surface of the IRS to fix the pixels. The rigid substrate helps ensure that the pixel spacing is almost unchanged during the stamp transfer process, and the weak and tunable adhesion facilitates the pixels being picked up by the stamp. The experimental results demonstrate that the pixels can be efficiently transferred to the IRS by LLO and sacrificial layer-assistance, which will provide the possibility of achieving the further transfer of pixels to different types and sizes of driving substrates by a suitable transfer stamp. The transfer process details are discussed, which can provide insights into the transfer of micro-nano devices through polymer sacrificial layers.
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| 3. |
- Pan, Kui, et al.
(author)
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Monolithically and Vertically Integrated LED-on-FET Device Based on a Novel GaN Epitaxial Structure
- 2023
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In: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 70:12, s. 6393-6398
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Journal article (peer-reviewed)abstract
- Optoelectronic devices, such as light-emitting diodes (LEDs), based on GaN-based semiconductor compounds are widely used for their advantages of long life, high reliability, and low energy consumption. The persistent challenge is integrating LED with transistors to achieve smaller size, lighter weight, higher speed, and more reliable optoelectronic integrated circuits. Here, we report monolithically and vertically integrated LED-on-FET devices fabricated on a novel GaN epitaxial structure. The designed device structure and fabrication process are simple. It also eliminates the extra area occupied by the transistor, and the shared n-GaN layer between the LED and FET reduces interconnect resistance and improves reliability. The measured threshold voltage (V-Th) of the LED-on-FET device is extrapolated as 3.9 V at the voltage (V-DD) of 5 V, and V-Th decreases with the increase of V-DD . More importantly, the gate voltage (V-GS) shows good performance in modulated electroluminescence (EL) intensity and switching capability of the LED. The integrated LED efficiently emits light modulation with a wavelength of 440 nm at V-DD= 9 V and V-GS=4-9 V (step = 1 V), which are necessary for devices in applications, such as displays and smart lighting. This epitaxy structure and integration scheme is promising in achieving large-scale optoelectronic integrated circuits, such as the next-generation micro-LED and nano-LED with super compact integrated drivers.
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| 4. |
- Zhang, Kai Xin, et al.
(author)
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Substrate-thickness dependence of negative-index metamaterials at optical frequencies
- 2024
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In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 124:10
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Journal article (peer-reviewed)abstract
- Optical metamaterials have attracted intensive attention in recent years for their broad applications in superlenses, electromagnetic cloaking, and bio-sensing. Negative refractive index (NRI) metal-dielectric-metal fishnet metamaterials (MMs) are typically used for beyond-diffraction-limit imaging. However, there are few reports about the substrate-thickness dependence of NRI, which strongly affects the practical application. In our study, it is demonstrated that the membrane-based NRI MMs with a more negative index work better than the bulk substrate-based counterparts. In addition, a regular periodic vibration of NRI with the thickness of the membrane substrate was theoretically studied. The destructive interference of the thin film can explain this phenomenon. Furthermore, the proposed explanation was further proved by substituting the dielectric spacer with a larger permittivity. Therefore, an NRI structure on a membrane substrate with constructive interference can be a good choice in ultra-compact photoelectronic devices. This study can be a guide to the practical application of ultracompact NRI devices.
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