Temperature effects for GaN films grown on 4H-SiC substrate with 4° miscutting orientation by plasma-assisted molecular beam epitaxy

The effects of growth temperatures and post-annealing treatment for GaN films by plasma-assisted molecular beam epitaxy are investigated. The heteroepitaxial GaN films were deposited on 4H-SiC substrates with 4° miscutting orientation at growth temperatures from 700 °C to 800 °C with a constant N/Ga flux ratio, while the post-annealing process was carried out at 800 °C for 10 min. GaN films are characterized by reflective high-energy electron diffraction, field-emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, high-resolution X-ray diffraction and photoluminescence spectroscopy. For the growth at the temperature of 750 °C, we can obtain a smooth surface, high percentages of GaN bond and low RGaO/GaN revealing a more stable composition on the surface. The higher crystalline structure of GaN films can be also obtained with the minimum of threading dislocation density. The sharpest near band edge emission and lowest defect band emission can be observed for GaN films grown at temperature of 800 °C. However, the surface roughness increases, and surface decomposition of GaN films occurs for the high-temperature growth. Moreover, post-annealing process can make the surface smoother, remove Ga droplets, and improve the stability of surface composition. After the post-annealing process, the increase of crystalline quality and optical property can be also demonstrated by the reduction of dislocation density and yellow band emission, respectively. In summary, the optimization of growth temperatures and post-annealing process can produce a high-quality GaN compound semiconductor for the applications in the future.