The Structural Evolution of Semipolar (11-22) Plane AlN Tem-Plate on m-Plane Sapphire Prepared by Sputtering and High Temperature Annealing.

In this work, the epitaxial semipolar (11-22) AlN was prepared on nonpolar m-sapphire substrate by combining sputtering and high-temperature annealing. According to our systematic measurements and analysis from XRD, Raman spectra, and AFM, the evolution of crystalline structure and morphology was investigated upon increasing AlN thickness and annealing duration. The annealing operation intensively resets the lattice and improves the crystalline quality. By varying the film thickness, the contribution from the AlN-sapphire interface on crystalline quality and lattice parameters during the annealing process was investigated, and its contribution was found to be not so obvious when the thickness increased from 300 nm to 1000 nm. When the annealing was performed under durations from 1 to 5 h, the crystalline quality was found unchanged; meanwhile, the evolution of morphology was pronounced, and it means the crystalline reorganization happens prior to morphology reset. Finally, the annealing treatment enabled a zig-zag morphology on the AlN template along the sapphire [0001] direction in the plane, which potentially affects the subsequent device epitaxy process. Therefore, our results act as important experience for the semipolar nitride semiconductor laser device preparation, particularly for the epitaxy of microcavity structure through providing the crystalline evolution.

Drive High Power UVC-LED Wafer into Low-Cost 4-Inch Era: Effect of Strain Modulation

Ultraviolet-C light-emitting diodes (UVC-LEDs) have great application in pathogen inactivation under various kinds of situations, especially in the fight against COVID-19. Unfortunately, its epitaxial wafers are so far limited to a size of 2 inches, which greatly increases the cost of massive production. In this work, a 4-inch crack-free high-power UVC-LED wafer is reported. This achievement relies on a proposed strain-tailored strategy, where a 3D to 2D (3D-2D) transition layer is introduced during the homo-epitaxy of AlN on the high temperature annealed (HTA)-AlN template, which successfully drives the original compressive strain into a tensile one and thus solves the challenge of realizing a high-quality Al0.6Ga0.4N layer with a flat surface. This smooth Al0.6Ga0.4N layer is nearly pseudomorphically grown on the strain-tailored HTA-AlN template, leading to 4-inch UVC-LED wafers with outstanding performances. The strategy succeeds in compromising the bottlenecked contradictory in producing a large-sized UVC-LED wafer on pronounced crystalline AlN template: The compressive strain in HTA-AlN allows for a crack-free 4-inch wafer, but at the same time leads to a deterioration of the AlGaN morphology and crystal quality. The launch of 4-inch wafers makes the chip fabrication process of UVC-LEDs match the mature blue one, and will definitely speed up the universal application of UVC-LED in daily life.