| 1. |
- Du, Zaifa, et al.
(author)
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Efficiency enhancement of micro-light-emitting diode with shrinking size by localized surface plasmons coupling
- 2024
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In: Applied Physics B: Lasers and Optics. - 0946-2171. ; 130:3
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Journal article (peer-reviewed)abstract
- The external quantum efficiency (EQE) enhancement of different sized GaN micro-light-emitting diodes (μLEDs) by using localized surface plasmons (LSPs) have been studied. Silver nanoparticles (Ag NPs) are attached to the sidewalls of μLEDs by spin-coating so as to be effectively coupled with the multiple quantum well (MQW) of μLEDs and generate the LSPs. In the μLEDs with 20 × 20 μm2 large mesas, the LSPs can effectively inhibit the efficiency droop. Compared to the μLED samples without the LSPs coupling, the EQE has been enhanced by about 8% at a high current density of 20,000 A/cm2. This work confirms the effectiveness of the LSPs technology in improving the μLED performances, which is originally practiced only on the basal faces of conventional LEDs.
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| 2. |
- Deng, Liying, et al.
(author)
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KCl acts as a flux to assist the growth of sub-millimeter-scale metallic 2D non-layered molybdenum dioxide
- 2024
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In: Rare Metals. - 1001-0521 .- 1867-7185. ; In Press
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Journal article (peer-reviewed)abstract
- Two-dimensional (2D) metal oxides (2DMOs), such as MoO2, have made impressive strides in recent years, and their applicability in a number of fields such as electronic devices, optoelectronic devices and lasers has been demonstrated. However, 2DMOs present challenges in their synthesis using conventional methods due to their non-van der Waals nature. We report that KCl acts as a flux to prepare large-area 2DMOs with sub-millimeter scale. We systematically investigate the effects of temperature, homogeneous time and cooling rate on the products in the flux method, demonstrating that in this reaction a saturated homogenous solution is obtained upon the melting of the salt and precursor. Afterward, the cooling rate was adjusted to regulate the thickness of the target crystals, leading to the precipitation of 2D non-layered material from the supersaturated solution; by applying this method, the highly crystalline non-layered 2D MoO2 flakes with so far the largest lateral size of up to sub-millimeter scale (~ 464 μm) were yielded. Electrical studies have revealed that the 2D MoO2 features metallic properties, with an excellent sheet resistance as low as 99 Ω·square−1 at room temperature, and exhibits a property of charge density wave in the measurement of resistivity as a function of temperature. Graphical abstract: TOC (Table of Content) (Figure presented.)
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| 3. |
- Fang, Xiubo, et al.
(author)
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Numerical modeling of GaN growth by MOCVD on metal substrate
- 2024
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In: Digest of Technical Papers - SID International Symposium. - 2168-0159 .- 0097-966X. ; 55:S1, s. 1059-1063
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Conference paper (peer-reviewed)abstract
- GaN materials have attracted great interest and have demonstrated remarkable potential in many fields. When growing GaN materials, substrate selection is of great importance. By virtue of their nominally unlimited size, easy removal, and excellent thermal conduction, metal substrates have been suggested as an alternative to the commonly used substrates such as sapphire. GaN growth on metal substrates, however, is still quite rare, and many aspects remain unexplored. This paper uses computational fluid dynamics to perform a three-dimensional numerical simulation of the GaNMOCVD reaction chamber. We investigated the influence of the graphite containers' rotational velocity and the metal matrix's temperature at various locations. When the pressure within the MOCVD chamber remains constant, increasing the graphite tray's rotational velocity enhances the temperature field distribution within the chamber. However, the flow field becomes unstable when the rotation rate exceeds 1000 rpm. Our findings serve as a crucial benchmark for the future parameter optimization of MOCVD growth of GaN on metals.
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| 4. |
- Lin, Jianpu, et al.
(author)
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Image segmentation by improved minimum spanning tree with fractional differential and Canny detector
- 2019
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In: Journal of Algorithms and Computational Technology. - : SAGE PUBLICATIONS LTD. - 1748-3018 .- 1748-3026. ; 13
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Journal article (peer-reviewed)abstract
- In this study, we propose an algorithm that uses an improved Minimum Spanning Tree algorithm and a modified Canny edge detector to segment images that contain a considerable amount of noises. First, we use our modified Canny operator to pre-process an image, and record the obtained object boundary information; then, we apply the improved Minimum Spanning Tree algorithm to associate the above information with boundary points in order to separate edges into two classes in the image, namely the inner and boundary regions. In particular, Minimum Spanning Tree algorithm is improved by using Fractional differential and combining the functions of the intra-regional and inter-regional differences with a function for edge weights. Based on the experimental results, compared with the other four exiting algorithms, the new algorithm has the higher accuracy and the better effect for noised image segmentation.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Pan, Kui, et al.
(author)
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Ultrasmall-sized light-emitting diodes fabricated by ion implantation based on GaN epitaxial wafers with fully activated or unactivated p-GaN
- 2024
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In: Optics Letters. - 0146-9592 .- 1539-4794. ; 49:17, s. 4835-4838
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Journal article (peer-reviewed)abstract
- A key challenge in realizing ultrahigh-resolution displays is the efficient preparation of ultrasmall-sized (USS) light-emitting diodes (LEDs). Today, GaN-based LEDs are mainly prepared through dry etching processes. However, it is difficult to achieve efficient and controllable etching of USS LED with high aspect ratios, and LED sidewalls will appear after etching, which will have a negative impact on the device itself. Herein, a method for preparing USS LED based on GaN epitaxial wafers is reported (on two types of wafers, i.e., with p-GaN fully activated and unactivated). F−ions are injected into the intentionally exposed areas on the two types of wafers to achieve device isolation. The area under the micro-/nanosized protective masks (0.5, 0.8, 1, 3, 5, 7, 9, and 10 µm wide Ni/Au stripes) are the LED lighting areas. The LED on the p-GaN unactivated wafer (UAW) requires further activation. The Ni/Au mask not only serves as the p-electrode of LED but also Ni as a hydrogen (H) removing metal covering the surface of p-GaN UAW that can desorb H from a Mg element in the film at relatively low temperatures, thereby achieving the selective activation of LED lighting areas. Optoelectronic characterization shows that micro-/nano-sized LED arrays with individual-pixel control were successfully fabricated on the two types of wafers. It is expected that the demonstrated method will provide a new way toward realizing ultrahigh-resolution displays. Analyzing the changes in the current flowing through LED (before and after selective activation) on the F−injected p-GaN UAW, it is believed that depositing H removing metal on p-GaN UAW could possibly realize the device array through the selective activation only (i.e., without the need for ion implantation), offering a completely new insight.
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| 8. |
- Wang, Shuaishuai, et al.
(author)
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Fabrication of Super Uniform Nickel Bumps Using Electroless Plating on Micro-LEDs’ TFT Driver Substrates
- 2024
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In: Digest of Technical Papers - SID International Symposium. - 2168-0159 .- 0097-966X. ; 55:S1, s. 194-196
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Conference paper (peer-reviewed)abstract
- In this study, in order to achieve high-yield Micro-LED chip bonding and thus further advance the breakthrough of Micro- LED interconnect technology. In this study, an electroless plating method is used to achieve the highly uniform nickel bump arrays on thin film transistor (TFT) driver substrate. Initially, the photoresists AZ4620 and AZ2070 are chosen for the experiments, which can cover the step structure uniformly of TFT substrate. Subsequently, the morphology of bumps on the TFT substrate influenced by the plasma treatment and the deposition time is investigated. The 1% uniformity of the nickel bump arrays by the electroless plating for 30 minutes after 5-minute plasma treatment is achieved, which lays the foundation for the electroless plating self-bonding.
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