Study on the effects of growth rate on GaN films properties grown by plasma-assisted molecular beam epitaxy

This work systematically investigates the effects of growth rate on GaN films properties grown on thick GaN-on-sapphire templates by plasma-assisted molecular beam epitaxy (PA-MBE) under Ga-rich conditions without formation of large metal droplets. The nitrogen-limited growth rate is varied by modulating the nitrogen flows while maintaining the power of radio frequency plasma source constant, and the thickness of epitaxial GaN films is determined by Capacitance-Voltage and verified by second ion mass spectroscopy simultaneously. It is found that GaN films grown at high growth rate exhibit an improved crystal quality measured by X-ray diffraction, and display a rough surface morphology along with higher hillocks and clearer step terrace resolved by atomic force microscopy. Photoluminescence spectroscopy characterization indicates the full width at half maximum of near band emission peak and intensity of yellow band emission are decreased for GaN epilayers grown at high growth rate, corresponding to a reduced density of defect states and a lowered concentration of residual carbon impurity, respectively. The presented results suggest that the growth rate strong influences the structural, morphological and optical properties of GaN epitaxial films, and high growth rate facilitates realizing a better GaN film quality, giving a conducive insight for PA-MBE-grown III-nitride device-quality materials for electronic and optoelectronic applications.