Alternating current (AC)-driven electroluminescent (EL) devices have attracted widespread attention due to their special advantages. Under the trend of nanoscale miniaturization in optoelectronics, AC-driven EL devices with nanoscale are highly desirable to be applied to nano-optoelectronic integrated circuits. In this work, GaN-based nanorod LEDs (nLED) are used as nanoscale emitters to fabricate AC-driven nano-EL device, namely, AC-nLED. Two configurations including single-dielectric AC-nLED and double-dielectric AC-nLED without carrier injection are demonstrated. The electrical and optical characteristics of single-dielectric AC-nLED and double-dielectric AC-nLED are demonstrated, which have completely different frequency responses. The working mechanisms and origin of the difference in frequency response are discussed. Our work presents an alternative device configuration for obtaining AC-driven nano-EL devices, which are expected to be used in nano-photonic systems and nano-pixel light-emitting displays.

Alternating current electroluminescence from GaN-based nanorod light-emitting diodes

Micro light-emitting diodes (μ-LEDs) coupled to color conversion phosphors are among the most promising technologies for future display and artificial light sources. However, current emitters suffer from excessively large particle sizes, preventing micron-scale processability, and/or low stability that hampers the device lifetime. Here, we demonstrate down-conversion μ-LED phosphors based on CsPbBr3 perovskite nanocrystals directly grown inside perfectly sealed mesoporous silica nanospheres (NSs). Key for this advancement is a high-throughput calcination procedure in the presence of K2CO3 as selective pore sealing agent, which simultaneously produces the CsPbBr3 nanocrystals, boosts their emission efficiency to >87%, and perfectly isolates them from the outer environment without causing inter-particle cross-linking or aggregation. This results in size-homogeneous, finely solution-dispersible, ultra-stable, and highly emissive CsPbBr3-SiO2 NSs that fit the technological requirements of photolithographic inks for highly uniform μ-LED color conversion patterns with pixels smaller than 20 μm. 

https://pubs.acs.org/doi/pdf/10.1021/acsenergylett.2c02062

Ultra-stable, Solution-Processable CsPbBr3-SiO2 Nanospheres for Highly Efficient Color Conversion in Micro Light-Emitting Diodes

MoS2‐based transparent electronics can revolutionize the state‐of‐the‐art display technology. The low‐temperature synthesis of MoS2 below the softening temperature of inexpensive glasses is an essential requirement, although it has remained a long persisting challenge. In this study, plasma‐enhanced chemical vapor deposition is utilized to grow large‐area MoS2 on a regular microscopic glass (area ≈27 cm2). To benefit from uniform MoS2, 7 × 7 arrays of top‐gated transparent (≈93% transparent at 550 nm) thin film transistors (TFTs) with Al2O3 dielectric that can operate between −15 and 15 V are fabricated. Additionally, the performance of TFTs is assessed under irradiation of visible light and estimated static performance parameters, such as photoresponsivity is found to be 27 A W−1 (at λ = 405 nm and an incident power density of 0.42 mW cm−2). The stable and uniform photoresponse of transparent MoS2 TFTs can facilitate the fabrication of transparent image sensors in the field of optoelectronics.

Low‐Temperature Plasma‐Assisted Growth of Large‐Area MoS2 for Transparent Phototransistors

This article presents a new micro-light-emitting diode (LED) pixel circuit driven by the digital pulsewidth modulation (PWM) method, in which the threshold voltage compensation of the driving thin-film transistor (TFT) is included. A scan driver integrated by metal oxide (MO) TFTs is also designed to provide the scan signals for pixel circuits array. A micro-LEDs array with $76\,\, \times $ BBB $\times \,\,78$ and a scan driver with 80 stages are simultaneously fabricated by MO TFTs backplane with back-channel etch (BCE) structure. A respective micro-LED display is consequently realized by a peripheral driving system based on a field-programmable gate array (FPGA), which is used as a core control unit to synchronize the scan signals with the data signals. It is shown that the micro-LED in the pixel circuit can operate at a constant current even at the 5- $\mu \text{s}$ pulsewidth of the emission (EM) signal. The micro-LED display can achieve 256 linear grayscales with an approximately 60 Hz flash rate under the minimum pulsewidth of 40 $\mu \text{s}$ of EM signal.

Active-Matrix Micro-LED Display Driven by Metal Oxide TFTs Using Digital PWM Method

Abstract Micro or submicron scale light-emitting diodes (µLEDs) have been extensively studied recently as the next-generation display technology. It is desired that µLEDs exhibit high stability and efficiency, submicron pixel size, and potential monolithic integration with Si-based complementary metal-oxide-semiconductor (CMOS) electronics. Achieving such µLEDs, however, has remained a daunting challenge. The polar nature of III-nitrides causes severe wavelength/color instability with varying carrier concentrations in the active region. The etching-induced surface damages and poor material quality of high indium composition InGaN quantum wells (QWs) severely deteriorate the performance of µLEDs, particularly those emitting in the green/red wavelength. Here we report, for the first time, µLEDs grown directly on Si with submicron lateral dimensions. The µLEDs feature ultra-stable, bright green emission with negligible quantum-confined Stark effect (QCSE). Detailed elemental mapping and numerical calculations show that the QCSE is screened by introducing polarization doping in the active region, which consists of InGaN/AlGaN QWs surrounded by an AlGaN/GaN shell with a negative Al composition gradient along the c -axis. In comparison with conventional GaN barriers, AlGaN barriers are shown to effectively compensate for the tensile strain within the active region, which significantly reduces the strain distribution and results in enhanced indium incorporation without compromising the material quality. This study provides new insights and a viable path for the design, fabrication, and integration of high-performance µLEDs on Si for a broad range of applications in on-chip optical communication and emerging augmented reality/mixed reality devices, and so on. 

/pdf/ingan-micro-light-emitting-diodes-monolithically-grown-on-si-in7tggb2.pdf

InGaN micro-light-emitting diodes monolithically grown on Si: achieving ultra-stable operation through polarization and strain engineering

Wafer-scale monolithic integration of full-colour micro-LED display using MoS2 transistor

A monolithic micro-LED display technology is proposed using a gallium-nitride-on-silicon substrate. An active matrix (AM) display was realized by interconnecting nitride-based LEDs as display pixels with Si thin-film transistors (TFTs) as driving circuitries. MOS TFTs were fabricated on a Si surface which had been exposed after dry etching of the LED epitaxial layer. The mobility and sub-threshold slope were measured as 354.3 cm2 V−1 s−1 and 0.64 V dec−1, respectively. A 150 pixel-per-inch 0.6 inch monolithic display was demonstrated with a 60 × 60 pixel array AM display by an integration technology on the same substrate.

https://iopscience.iop.org/article/10.7567/1882-0786/ab64ff/pdf

A monolithically integrated micro-LED display based on GaN-on-silicon substrate

Abstract A flexible full-color micro-LED display with high mechanical robustness was fabricated by printing quantum dots (QDs) on a blue micro-LED array using standard photolithography. The red and green colors yielded from QDs exhibit a better color gamut than conventional color filters. The light conversion efficiency was enhanced by adding TiO 2 nanoparticles to the QD-photoresist composite. This full-color micro-LED display was successfully mounted on various unusual substrates such as curved glass, fabrics, and human skin, enabling diverse optoelectronic applications. In addition, wireless multi-channel visible light communication (VLC) based on the wavelength-division-multiplexing orthogonal-frequency-division-multiplexing (WDM-OFDM) technique was demonstrated using a QD-based color micro-LED panel. A high data transmission rate of 1.9 Gbps was successfully obtained owing to the high electrical–optical modulation bandwidth of the QD-based micro-LED panel. 

https://www.nature.com/articles/s41528-022-00234-z.pdf

Jae Yong Choi

Papers

Wafer-scale monolithic integration of full-colour micro-LED display using MoS2 transistor

A monolithically integrated micro-LED display based on GaN-on-silicon substrate

Flexible micro-LED display and its application in Gbps multi-channel visible light communication