Impact of nucleation temperature on growth uniformity of GaN on 4-inch dome-patterned sapphire substrate

Considerable demands for energy-efficient visible LEDs nowadays have led to a pressing need for high-quality GaN/sapphire templates with large diameters. One of the major challenges to achieve the goal is to obtain good growth uniformity across the entire area of the templates. This paper attempts to improve the growth uniformity for GaN layers on 4-inch dome-patterned sapphire substrate (DPSS) by optimising the GaN nucleation temperature. Here, the nucleation temperature was varied at 520 degrees C, 550 degrees C, 570 degrees C, 590 degrees C, and 620 degrees C. In comparison to the case with 520 degrees C and 620 degrees C nucleation, the threading dislocation density (TDD) at three different positions (i.e. centre, half-radius on the right side and half-radius on the left side) of the GaN layers grown with 550 degrees C-590 degrees C nucleation was relatively lower and the result was consistent among the positions. Meanwhile, the average in-plane strain was higher for these GaN layers compared to the case with 520 degrees C and 620 degrees C nucleation. This might be associated with the improvement of the crystalline structure of the layers. Moreover, for the GaN layers with the nucleation of 520 degrees C-590 degrees C, the surface was atomically smoother and showed step-flow characteristics at the three positions. It can be suggested that the nucleation at 520 degrees C-590 degrees C favoured the growth on the trenches rather than the sidewalls, thereby suppressing multiple growth orientations. Subsequently, an InGaN blue LED was grown on GaN layer with the optimised nucleation temperature. It was found that the electrical and optical characteristics of different LED chips are fairly uniform.