在p?AlGaN表面沉积Ni/Au/Ni/Au透明电极体系，通过传输线模型测试，研究了退火温度对Ni/Au/Ni/Au与p?AlGaN材料接触特性的影响。结果表明，AlGaN基深紫外LED采用Ni/Au/Ni/Au金属体系，在600 ℃空气氛围下退火3 min形成p型半导体材料NiO。进一步优化Ni/Au/Ni/Au体系金属厚度，当Ni/Au/Ni/Au各层厚度由20/20/20/20 nm减薄至2/2/5/5 nm，并在600 ℃空气氛围退火3 min，其与p?AlGaN材料的接触电阻率从3.23×10^-1 Ω·cm²降到2.58×10^-4 Ω·cm²。采用上述优化的Ni/Au/Ni/Au体系制备的深紫外LED器件，器件光电特性得到了改善。在150 mA驱动下工作电压低至5.8 V；通过提升电极透过率，光输出功率提升18.9%。

High-quality AlN/sapphire templates were fabricated by the combination of sputtering and high-temperature (HT) annealing. The influence of sputtering parameters including nitrogen flux, radio frequency power, and substrate temperature on the crystalline quality and surface morphology of annealed AlN films were investigated. With lower substrate temperature, lower power, and lower N₂ flux, the full width at half maximum of the X-ray rocking curve for AlN (0002) and (10 2) were improved to 97.2 and 259.2 arcsec after high-temperature annealing. This happens because the increased vacancy concentration of sputtered AlN films can facilitate the annihilation of dislocations by increasing the recovery rate during HT annealing. Step and step-bunching morphologies were clearly observed with optimized sputtering conditions.

To achieve high quality lighting and visible light communication (VLC) simultaneously, GaN based white light emitting diodes (WLEDs) oriented for lighting in VLC has attracted great interest. However, the overall bandwidth of conventional phosphor converted WLEDs is limited by the long lifetime of phosphor, the slow Stokes transfer process, the resistance-capacitance (RC) time delay, and the quantum-confined Stark effect (QCSE). Here by adopting a self-assembled InGaN quantum dots (QDs) structure, we have fabricated phosphor-free single chip WLEDs with tunable correlated color temperature (CCT, from 1600 K to 6000 K), a broadband spectrum, a moderate color rendering index (CRI) of 75, and a significantly improved modulation bandwidth (maximum of 150 MHz) at a low current density of 72A/cm2. The broadband spectrum and high modulation bandwidth are ascribed to the capture of carriers by different localized states of InGaN QDs with alleviative QCSE as compared to the traditional InGaN/GaN quantum well (QW) structures. We believe the approach reported in this work will find its potential application in GaN WLEDs and advance the development of semiconductor lighting-communication integration.

This study focused on the evolution of growth front about AlN growth on nano-patterned sapphire substrate by metal-organic chemical vapor deposition. The substrate with concave cones was fabricated by nano-imprint lithography and wet etching. Two samples with different epitaxy procedures were fabricated, manifesting as two-dimensional growth mode and three-dimensional growth mode, respectively. The results showed that growth temperature deeply influenced the growth modes and thus played a critical role in the coalescence of AlN. At a relatively high temperature, the AlN epilayer was progressively coalescence and the growth mode was two-dimensional. In this case, we found that the inclined semi-polar facets arising in the process of coalescence were type. But when decreasing the temperature, the semi-polar facets arose, leading to inverse pyramid morphology and obtaining the three-dimensional growth mode. The 3D inverse pyramid AlN structure could be used for realizing 3D semi-polar UV-LED or facet-controlled epitaxial lateral overgrowth of AlN.

Metallic nanotextured reflectors have been widely used in light emitting diodes (LEDs) to enhance the light extraction efficiency. However, the light absorption loss for the metallic reflectors with nanotexture structure is often neglected. Here, the influence of absorption loss of metallic nanotextured reflectors on the LED optoelectronic properties were studied. Two commonly used metal reflectors Ag and Al were applied to green GaN-based LEDs. By applying a Ag nanotextured reflector, the light output power of the LEDs was enhanced by 78% due to the improved light extraction. For an Al nanotextured reflector, however, only a 6% enhancement of the light output power was achieved. By analyzing the metal absorption using finite-difference time-domain (FDTD) and the metal reflectivity spectrum, it is shown that the surface plasmon (SP) intrinsic absorption of metallic reflectors with nanotexture structure play an important role. This finding will aid the design of the high-performance metal nanotextured reflectors and optoelectronics devices.

The nanorod structure is an alternative scheme to develop high-efficiency deep ultraviolet light-emitting diodes (DUV LEDs). In this paper, we first report the electrically injected 274-nm AlGaN nanorod array DUV LEDs fabricated by the nanosphere lithography and dry-etching technique. Nanorod DUV LED devices with good electrical properties are successfully realized. Compared to planar DUV LEDs, nanorod DUV LEDs present >2.5 times improvement in light output power and external quantum efficiency. The internal quantum efficiency of nanorod LEDs increases by 1.2 times due to the transformation of carriers from the exciton to the free electron–hole, possibly driven by the interface state effect of the nanorod sidewall surface. In addition, the nanorod array significantly facilitates photons escaping from the interior of LEDs along the vertical direction, contributing to improving light extraction efficiency. The three-dimensional finite-different time-domain simulation is performed to further analyze in detail the TE- and TM-polarized photons extraction mechanisms of the nanostructure. Our results demonstrate the nanorod structure is a good candidate for high-efficiency DUV emitters.