10:45 AM - 11:00 AM
[15a-503-7] The role of surface kinetics on AlN and Al-rich AlGaN
Keywords:III-Nitride materials
AlN based AlGaN technology offers a great potential as materials for deep UV optoelectronic and high-power electronic devices. In order to realize such devices, high quality epitaxial films with controlled surface morphology are necessary. We have developed a surface kinetic framework for the control of surface morphology of AlN epitaxial thin films grown on both vicinal (0001)-oriented native single crystal AlN substrates and AlN templates grown on vicinal (0001)-oriented sapphire. A Burton, Cabrera, and Frank (BCF) theory-based model is utilized to understand the dependence of the surface kinetics on the vapor supersaturation and substrate misorientation angle. The surface energy of the Al-polar surface of AlN was experimentally determined using BCF theory to be 149 ± 8 meV/Å2. The critical misorientation angle for the onset of step-bunching was determined to be ~0.2° for a growth rate of 500 nm/h and temperature of 1250 °C (Fig. 1). Transitioning from a surface with 2D nuclei to one with bilayer steps required a decrease in the vapor supersaturation or an increase in substrate misorientation angle, whereas the suppression of step-bunching required an increase in the vapor supersaturation or decrease in substrate misorientation angle. We extended the same framework of surface kinetic model in AlN growth to the case of Al-rich AlGaN growth. The composition of bilayer stepped AlGaN was uniformed, while step-bunching resulted in strong compositional inhomogeneity as observed by Z-contrast STEM (Fig. 2). Quantum efficiencies were lower for MQWs grown on step-bunched surfaces as opposed to bilayer stepped surfaces. These results demonstrate a control scheme for consistently obtaining smooth Al-rich AlGaN epitaxial thin films needed for improving the efficiency of heterostructure- and superlattice-based devices.