To obtain excellent current spreading performance of ultraviolet light-emitting diodes (UVLEDs), a 60-period stacked Si modulation-doped n-AlGaN/u-GaN structure is proposed to replace the traditional n-AlGaN structure. The high-resolution X-ray diffraction ω-scan rocking curves show that the periodic growth of AlGaN and GaN layers plays a positive role in reducing dislocation density. Compared with the conventional UV light-emitting diodes (LEDs), light emission micrographs of devices with a multi-layer stacked n-AlGaN/u-GaN structure reveal higher brightness and a more uniform distribution. In addition, the output power and external quantum efficiency under a 20-mA injection current are increased by 22% and 26.5%, respectively. Experimental and simulation results indicate that a multi-layer stacking structure can alleviate the current crowding effect in four ways:(1) a reduction in dislocation density; (2) replacement of quasi-two-dimensional electron transport with electronic bulk transport to enhance electron mobility; (3) an increase in electron concentration without improving the impurity concentration; and (4) a weakening of the electron scattering effect by reducing the impurity concentration.

In this paper, the conditions of the dip-coating method of SiO2 nanospheres are optimized, and a neatly arranged single-layer SiO2 array is obtained. On this basis, a “top-down” inductively coupled plasma (ICP) technique is used to etch the p-GaN layer to prepare a periodic triangular nanopore array. After the etching is completed, the compressive stress in the epitaxial wafer sample is released to a certain extent. Then, die processing is performed on the etched LED epitaxial wafer samples. The LED chip with an etching depth of 150 nm has the highest overall luminous efficiency. Under a 100 mA injection current, the light output power (LOP) of the etched 150 nm sample is 23.61% higher than that of the original unetched sample.

Magnetron sputtering is adopted to deposit ~25 nm thick AlN on the surface of hexagonal BN(h-BN)/sapphire substrates, followed by epitaxial GaN growth on top of the AlN/h-BN/sapphire substrate using a metal–organic chemical vapor deposition system. Compared to GaN grown on the h-BN/sapphire surface directly, this method results in a continuous and smooth GaN film with a smaller root mean square roughness. Besides, the introduction of the sputtered AlN layer reduces the dislocation density of GaN by 35.7%. We provide a pathway of GaN epitaxy on the h-BN surface, which significantly improves its surface morphology and crystal quality.

The lower luminous efficiency is a critical issue for ultraviolet light-emitting diodes (UV-LEDs) owing to the poor carrier injection efficiency and high dislocation density. Here, we can improve the luminous efficiency in two avenues by adjusting the Al composition of the InGaN/AlxGa1-xN pre-well superlattice. First, due to the strain-induced piezoelectric and intrinsic spontaneous polarization, a large number of electrons gather at the InGaN/AlxGa1-xN interface, which improves the electron concentration of the pre-well superlattice and lowers the conduction band energy of the first quantum barrier layer (FQB), thus enhancing the electron injection efficiency. Second, the pre-well superlattice can act as a hole blocking layer to prevent holes from leaking into the n-type layer and confine them in the quantum well layer. As the Al composition increases, the hole blocking effect of the pre-well superlattice is strengthened. However, higher Al composition decreases the lattice quality, which makes it possible for carrier loss through defect-related non-radiative recombination. Finally, the output power of the samples with 5% Al composition in the pre-well superlattice is 5.9% and 102.5% higher than that of the samples with 3% and 7% Al composition, respectively.