In this study, a nano-columnar low-temperature (LT) GaN buffer was used to reduce the wafer bowing of a GaN layer grown on a sapphire substrate. A significant reduction in the extent of wafer bowing was observed for the GaN layer for the preserved nano-columnar LT GaN layer when compared with the conventional GaN layer. These results suggest that the preserved nano-columnar structure helped relax the GaN layer strain energy associated with thermal expansion mismatch. The flow of TMGa during the temperature ramp-up from LT to high-temperature was found to be an important process parameter to preserving the nano-columnar structure of LT GaN, resulting in less bowed GaN on sapphire.
- Nano-columnar microstructure of low-temperature GaN was preserved in GaN layer.
- Flow of TMGa during temperature ramp-up was essential for the microstructure.
- It induced tensile stress in GaN layer, resulting in reduced wafer bowing.
Fig. 1. (a) Plan-view SEM image, (b) cross-sectional TEM image of the LT GaN layer grown at 570 °C on a sapphire substrate.
Source: Seoul National University
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