Erdan Gu

GaN-based micro-light-emitting diodes (micro-LEDs) have great advantages in visible light communication (VLC). However, the limited external quantum efficiency (EQE) and the modulation bandwidth of green micro-LEDs have been the obstacles of improvement in the data rates of the VLC system. In this work, a straightforward and efficacious approach is employed to improve the VLC performance of the micro-LEDs, that is, etching epitaxial layers to a sapphire substrate using deep-etching processes to fabricate each micro-LED electrically isolated arrays. Compared to micro-LEDs with a common n-type GaN layer, the deep-etched micro-LEDs exhibit enhanced light output power from the sapphire side and increased −3 dB bandwidth, owing to the reduced n-GaN waveguiding effect and parasitic capacitance, resulting in 47.03% and 57.33% improvements in EQE and −3 dB bandwidth at 4 kA/cm2, respectively. As a result, the deep-etched green micro-LED based VLC system achieved a maximum data rate of 6.58 Gbps by employing an orthogonal frequency division multiplexing modulation scheme and a pre-equalization method, which represents the highest data rate for a single green micro-LED.

Electron backscatter diffraction and cathodoluminescence are complementary scanning electron microscopy modes widely used in the characterisation of semiconductor films, respectively revealing the strain state of a crystalline material and the effect of this strain on the light emission from the sample. Conflicting beam, sample and detector geometries have meant it is not generally possible to acquire the two signals together during the same scan. Here, we present a method of achieving this simultaneous acquisition, by collecting the light emission through a transparent sample substrate. We apply this combination of techniques to investigate the strain field and resultant emission wavelength variation in a deep-ultraviolet micro-LED. For such compatible samples, this approach has the benefits of avoiding image alignment issues and minimising beam damage effects.

We report a Deep Ultraviolet (DUV) AlGaN micro-light emitting diode (micro-LED) array driven by a matching array of electronic drivers implemented in Complementary Metal-Oxide-Semiconductor (CMOS) technology. This 40 × 10 pixel integrated device required improvements in micro-LED fabrication combined with control over the LED ground level in the custom designed CMOS chip. It allows each of the micro-LEDs, with a measured peak emission wavelength of 271 nm, to be addressed independently in continuous wave (CW) or nanosecond pulsed operation, with optical output powers and pulse energies per pixel of 80 μW and 0.2 pJ, respectively. Performance of this high-resolution electronically-driven array for multi-channel UV-C wireless communications is given as an example of its potentially wide-ranging uses.

We report systematic investigation of the device-sizedependent performance of ultraviolet C (UV-C) light emitting diodes (LEDs) for optical wireless communication (OWC). Utilizing 273 nm-wavelength devices with diameters in the range of 40 μm to 300 μm, the size-dependent electrical, optical and frequency response characteristics of AlGaN UV-C LEDs are analyzed. As the junction area scales down, the smaller devices present lower optical power but faster modulation speed. Based on a 1-m point-to-point OWC system, this study further explores the LED size effect on the communication performance including channel gain, signal-to-noise ratio (SNR), theoretical Shannon capacity, achievable data transmission rate, relevant ratio, and spectral efficiency (SE). The system employing a 60 μm diameter (micro) LED transmitter achieves the highest average SNR and SE accompanying a data transmission rate up to a 5.53 Gbps at the forward error correction floor of 3.8×10 ⁻³ . These results suggest an optimal device diameter of ∼60 μm for further development of high-performance UV-C short-range line-of-sight (LoS) OWC.

We propose and demonstrate a GaN-based series-driven hybrid light emitting diode (SH-LED) device in which broad-area and micro-LED components are interconnected for simultaneous illumination and high-speed visible light communication (VLC) applications. Through theoretical analysis based on an equivalent electrical circuit model and characterization from a fabricated exemplar device with blue emission, it is shown that SH-LEDs combine the advantages of broad-area and micro-LED components by offering high direct-current (DC) optical power output and a fast frequency response. The application of this device to VLC is demonstrated through both the point-to-point and 9 $^\circ$ divergence-angle coverage systems at 3 m transmission distance adopting a DC-biased optical-orthogonal frequency-division multiplexing modulation scheme. Compared with a point-to-point system using a single micro-LED, that our initial demonstrator SH-LED achieves the same data transmission rate of 3.39 Gbps at forward error correction (FEC) floor of 3.8 $\times\; 10^{-3}$ , but the received DC optical power is improved by over 3 times. For the area coverage system, up to 1.56 Gbps data transmission rates at a FEC floor of 3.8 $\times\; 10^{-3}$ are accomplished by using this device, associated with over 4 times higher received DC optical power compared with that using a single micro-LED.

μLED has advantages in brightness, power consumption and response speed. In addition, μLED can also be used as micro sensors implanted in the body via flexible electronic skin. One of the key technology is the transfer printing of μLED. Although numerous methods have been proposed for transfer printing technology, improving the yield of μLED array is still a formidable task. In this paper, we proposed a novel method in improving the yield of μLED array, transferred by the stamping method, using an innovative design of piezoelectric driven asymmetric micro gripper. A μLED manipulation system was constructed based on a micro gripper of a three dimensional positioning system. The experimental results showed that this system could be used to manipulate μLED array.

High speed wireless communications are highly desirable for many industrial and scientific underwater applications. Acoustic communications suffer from high latency and limited data rates, while Radio Frequency communications are severely limited by attenuation in seawater. Optical communications are a promising alternative, offering high transmission rates (up to Gb/s), while water has relatively low attenuation at visible wavelengths. Here we demonstrate the use of series-connected micro-light-emitting-diode (μLED) arrays consisting of 6 μLED pixels either 60 μm or 80 μm in diameter and operating at 450 nm. These devices increase the output power whilst maintaining relatively high modulation bandwidth. Using orthogonal frequency division multiplexing (OFDM) we demonstrate underwater wireless data transmission at rates of up to 4.92 Gb/s, 3.22 Gb/s and 3.4 Gb/s over 1.5 m, 3 m and 4.5 m, respectively, with corresponding bit error ratios (BERs) of 1.5×10-3, 1.1×10-3 and 3.1×10-3, through clear tap water, and Mb/s rates through >5 attenuation lengths (ALs) in turbid waters.

This paper proposes a novel GaN-based LED with nano-grating structure based on surface plasmons. This structure mainly contains n-GaN, multiple quantum wells and p-GaN, Ag-SiO2 grating, core-shell Ag/SiO2 nanoparticle and ITO triangular grating. The basic principle of the light emitting characteristics of LED is described in detail. The COMSOL software is used to analyse properties and optimise parameters based on the finite element method. The radiated intensity, absorbed intensity and electric field distribution are obtained. The results indicate that this structure has a higher luminous efficiency with the luminous intensity increased to about 58.59 times compared with the ordinary structure and about 3.94 times compared with the reference structure, and can enhance the internal quantum efficiency and the external quantum efficiency of the LED simultaneously.

Integrated blue-violet and blue-green micro-LED arrays, fabricated via a transfer printing method, were employed to demonstrate wavelength division multiplexing underwater data transmission at 100 Mb/s over up to 9 attenuation lengths in a 1.5 m long water tank.