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. [ABSTRACT FROM AUTHOR]