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The quantum dot (QD) color-conversion efficiency (CCE) in GaN micro-light-emitting diodes ( $\mu $ LEDs) is greatly improved by non-radiative energy transfer (NRET) mechanism. An array of deep nano-holes with a diameter of about $1~\mu \text{m}$ was fabricated in $\mu $ LED mesas ( $40\times 60\,\,\mu \text{m}^{2}$ ) by nanoimprint lithography. The nano-holes were etched straight through the $\mu $ LED active region to ensure that the filled QDs were in extremely close contact with the active region. The absorption efficiency and emission efficiency of QDs are effectively improved by NRET, resulting in a superhigh CCE in QD- $\mu $ LED hybrid devices. Compared to $\mu $ LED devices with conventional spin-coated QDs, the CCE of novel nano-hole $\mu $ LEDs with filled QDs has been enhanced by about 118%.

Using the plasma-enhanced chemical vapor deposition method, we grow vertical graphene thin films onto SiO2/Si substrates, which is a special format of graphene composed of numerous macroscopically uniformly distributed graphene flakes approximately vertically arranged. The growth parameters, including the growth temperature, growth time and plasma power, are systematically studied and optimized. Most importantly, the function of plasma has been revealed. In the same deposition machine, we have altered the plasma electrode and heater configurations, and found that the vertical graphene can only grow in local plasma environment. That is, the samples have to be well immersed in the plasma sheath electric field. In this way, the vertical growth of graphene and the local enhancement of electric field can form a positive feedback loop, resulting in the continuous growth of vertical graphene. This experiment clarifies the function of plasma electric field in the vertical graphene growth, and can offer hints for the growth of other vertical two-dimensional materials as well. The vertical graphene films are scalable, transfer-free and lithographically patternable, which is compatible with standard semiconductor processing and promising for optoelectronic applications. We have characterized the optical properties of the as-grown vertical graphene films, where a nearly zero transmittance is observed for 1100–2600[Formula: see text]nm wavelengths, indicating a superstrong absorption in the black colored vertical graphene.

Currently, applying graphene on GaN based electronic devices requires the troublesome, manual, lengthy, and irreproducible graphene transfer procedures, making it infeasible for real applications. Here, a semiconductor industry compatible technique for the in situ growth of patterned graphene directly onto GaN LED epiwafers for transparent heat-spreading electrode application is introduced. Pre-patterned sacrificial Co acts as both an etching mask for the GaN mesa and a catalyst for graphene growth. The Co helps in catalyzing the hydrocarbon decomposition and the subsequent graphitization, and is removed by wet etching afterwards. The use of plasma enhancement in the graphene chemical vapor deposition reduces the growth temperature to as low as 600 °C and improves the graphene quality, where highly crystalline graphene can be obtained in just 2 min of deposition. This method reduces the exposure of the GaN epilayers to high temperature to its limit, avoiding the well-known GaN decomposition and In segregation problems. Importantly, it can directly pattern the graphene without using additional lithographic steps and in doing so avoids any unintentional deleterious doping and damage of graphene from contact with the photoresist. The approach simplifies the fabrication and enables mass production by eliminating the bottlenecks of graphene transfer and patterning procedures. By comparing the GaN LEDs with and without graphene, we find that graphene greatly improves the device optical, electrical and thermal performances, due to the high optical transparency (91.74%) and high heat spreading capability of the graphene electrode. Unlike transferred graphene, this method is intrinsically scalable, reproducible, and compatible with the planar process, and is beneficial to the industrialization of GaN-graphene optoelectronic devices, where the integrated graphene serves as a superior sustainable and functional substitute to other transparent conducting materials such as ITO.

A technique for the in situ growth of patterned graphene by CVD has been achieved directly on insulating substrates at 800 degrees C. The graphene growth is catalyzed by a Ni-Cu alloy sacrificial layer, which integrates many advantages such as being lithography-free, and almost wrinkle-free, with a high repeatability and rapid growth. The etching method of the metal sacrificial layer is the core of this technique, and the mechanism is analyzed. Graphene has been found to play an important role in accelerating etching speeds. The Ni-Cu alloy exhibits a high catalytic activity, and thus, high-quality graphene can be obtained at a lower temperature. Moreover, the Ni-Cu layer accommodates a limited amount of carbon atoms, which ensures a high monolayer ratio of the graphene. The carbon solid solubility of the alloy is calculated theoretically and used to explain the experimental findings. The method is compatible with the current semiconductor process and is conducive to the industrialization of graphene devices.

One of the major bottlenecks in the commercialization of micro-light-emitting diodes (micro-LEDs) displays is the “massive transfer”. Monolithic integration of the driving element and the micro-LED pixel can radically avoid the technical problem of massive transfer. In this paper, the integrated device was fabricated on a gallium nitride (GaN) substrate. The device uses graphene as the channel material for the driving field-effect transistors (FETs) to control the micro-LEDs. However, in the traditional process, the residue of the ultraviolet photoresist on the surface of the graphene will cause severe doping, which resulting in the inferior performance of the fabricated graphene FETs (GFETs) device. To get higherperformance integrated devices, a new process method was intended in this paper. The performance of the GFETs was enhanced by optimizing the fabrication process, and the current control range of the GFETs for micro-LED was up to 11mA. The new process method adopts the PMMA thin film underlayer photolithography method, which effectively avoids the severe doping problem caused by ultraviolet photoresist residues on the graphene surface when fabricating GFETs for integrated devices. Based on the new fabricating technology, the transconductance and carrier mobility of GFETs had significantly enhanced. In conclusion, this research further expands the application of two-dimensional materials in the field of optoelectronic displays. Furthermore, the application of the new fabrication process of the integrated devices can be used as a technology accumulation to promote the commercialization of micro-LEDs.

NH-μLED, namely a micro light-emitting diode structure with nano-holes dug all the way through the active region, is designed to make silver nanoparticles in extremely close contact with the quantum wells for improving the coupling between the localized surface plasmon and the quantum wells (LSP-QWs coupling) and thus enhancing the optical properties of the μLED. The experimental results show that, thanks to this deep nanohole structure, the LSP-QWs coupling can be realized effectively, which ultimately increases the optical performance of the μLED. The internal quantum efficiency of the NH-μLED filled with silver nanoparticles is increased by 12%, and the final optical output power is also enhanced. We have further carried out a comparison study which measures the transient lifetime of two different types of μLEDs, and the results provide convincing evidence for the existence of the ultra close range LSP-QWs coupling effect.

A strategy for the application of localized surface plasmon to Micro-LED is proposed in this paper. The quantum wells region is exposed by direct etching and Ag nanoparticles is used to generate localized surface plasmon.

High-quality graphene was obtained directly on GaN epiwafers at low temperature using the metal proximity catalytic effect. Metal catalyse graphene without contacting with it ensure high performance of graphene-GaN LED.

Deep reactive ion etching (DRIE) technology is one of the most important technologies in the processing of microelectronic devices and microelectromechanical system. As a necessary process in semiconductor integration, it has been widely studied in the past decades. It is known that the traditional DRIE process typically uses a plasma etching reactor equipped with inductively coupled plasma (ICP) sources to generate a high-density plasma so as to achieve high aspect ratio trenches with relatively small roughness. A cryogenic temperature control unit is typically employed as well. Here, however, we use a parallel plate RIE with rather simple structure, which is not usually used for DRIE, to obtain high aspect ratio silicon etching. With no ICP sources and no sophisticated temperature control unit, the system and experiment are now much more cost effective. Through the optimization of the processing, the etching rate of silicon can reach 440 nm/min. Finally, a 45 μm deep trench is etched in silicon with good perpendicularity. This method will greatly reduce the equipment related cost, especially for those applications that do not have extremely stringent requirement on the final etching accuracy.

Arc discharge is traditionally used to synthesize randomly arranged graphene flakes. In this paper, we substantially modify it into a glow discharge method so that the discharge current is much more reduced. The H2 and/or Ar plasma etching of the graphitic electrode (used to ignite the plasma) is hence much gentler, rendering it possible to grow graphene in thin film format. During the growth at a few mbar, there is no external carbon gas precursor introduced. The carbon atoms and/or carbon containing particles as a result of the plasma etching are emitted in the chamber, some of which undergo gas phase scattering and deposit onto the metallic catalyst substrates (Cu-Ni alloy thin films or Cu foils) as graphene sheets. It is found that high quality monolayer graphene can be synthesized on Cu foil at 900 &deg, C. On Cu-Ni, under the same growth condition, somewhat more bilayer regions are observed. It is observed that the material quality is almost indifferent to the gas ratios, which makes the optimization of the deposition process relatively easy. Detailed study on the deposition procedure and the material characterization have been carried out. This work reveals the possibility of producing thin film graphene by a gas discharge based process, not only from fundamental point of view, but it also provides an alternative technique other than standard chemical vapor deposition to synthesize graphene that is compatible with the semiconductor planar process. As the process uses solid graphite as a source material that is rich in the crust, it is a facile and relatively cheap method to obtain high quality graphene thin films in this respect.

Co acts as both an etching mask and a catalyst for the growth of grapheme, high- quality graphene can be obtained quickly and at low temperatures for transparent electrode applications on GaN LEDs.

In this work, we grew transfer-free graphene-like thin films (GLTFs) directly on gallium nitride (GaN)/sapphire light-emitting diode (LED) substrates. Their electrical, optical and thermal properties were studied for transparent electrode applications. Ultrathin platinum (2 nm) was used as the catalyst in the plasma-enhanced chemical vapor deposition (PECVD). The growth parameters were adjusted such that the high temperature exposure of GaN wafers was reduced to its minimum (deposition temperature as low as 600 &deg, C) to ensure the intactness of GaN epilayers. In a comparison study of the Pt-GLTF GaN LED devices and Pt-only LED devices, the former was found to be superior in most aspects, including surface sheet resistance, power consumption, and temperature distribution, but not in optical transmission. This confirmed that the as-developed GLTF-based transparent electrodes had good current spreading, current injection and thermal spreading functionalities. Most importantly, the technique presented herein does not involve any material transfer, rendering a scalable, controllable, reproducible and semiconductor industry-compatible solution for transparent electrodes in GaN-based optoelectronic devices.

Graphene nanowalls (GNWs) are wall-like graphene nanosheets that are oriented vertically on a substrate. GNWs have a unique structure and special optoelectronic properties, which enables their use in photodetectors. In this paper, we use plasma-enhanced chemical vapor deposition to directly grow GNWs onto the surface of an n-type lightly doped Si substrate and to optimize the quality of the GNWs by adjusting the growth time and temperature. Furthermore, after the GNWs are lithographically patterned, we use a GNW-Si Schottky structure to develop photodetector arrays which are capable of detecting light from the visible to infrared light spectral range. Throughout the process, GNWs are directly synthesized on a Si substrate without using a catalyst or a transfer step. The process is simple and efficient. Under laser illumination at a wavelength of 792 nm, the highest on/off ratio at zero bias is approximately 105, and the specific detectivity is 7.85 × 106 cm Hz1/2/W. Under a reverse bias of 4 V, the measured responsivity of the detector reaches 1 A/W at room temperature. The device can also produce a light response in the near-infrared band. Upon laser illumination at a wavelength of 1550 nm, the detector shows a responsivity of 12 mA/W at room temperature.

Micro-light-emitting diodes (micro-LEDs) are the key to next-generation display technology. However, since the driving circuits are typically composed of Si devices, numerous micro-LED pixels must be transferred from their GaN substrate to bond with the Si field-effect transistors (FETs). This process is called massive transfer, which is arguably the largest obstacle preventing the commercialization of micro-LEDs. We combined GaN devices with emerging graphene transistors and for the first-time designed, fabricated, and measured a monolithic integrated device composed of a GaN micro-LED and a graphene FET connected in series. The p-electrode of the micro-LED was connected to the source of the driving transistor. The FET was used to tune the work current in the micro-LED. Meanwhile, the transparent electrode of the micro-LED was also made of graphene. The operation of the device was demonstrated in room temperature conditions. This research opens the gateway to a new field where other two-dimensional (2D) materials can be used as FET channel materials to further improve transfer properties. The 2D materials can in principle be grown directly onto GaN, which is reproducible and scalable. Also, considering the outstanding properties and versatility of 2D materials, it is possible to envision fully transparent micro-LED displays with transfer-free active matrices (AM), alongside an efficient thermal management solution.