Surface morphology evolution of m-plane (1ī00) GaN during MBE growth: impact of III/V ratio and miscut direction
Jiayi Shao and Liang Tang
Recently the nonpolar surfaces (m-plane and a-plane) of GaN have attracted significant interest as there is no spontaneous built-in piezoelectric field along these growth directions. Considerable effort has been devoted into the study of nonpolar GaN growth by metalorganic vapour phase epitaxy (MOCVD) and plasma-assisted molecular beam epitaxy (PAMBE). For PAMBE homoepitaxy along the c-axis, it is well known that the III-V flux ratio will have an enormous impact on the resulting surface morphology. In this work, we investigate the homoepitaxial growth of m-plane GaN by PAMBE with small miscuts towards –c and +c axes miscut under both nitrogen-rich and metal-rich conditions. Interestingly m-plane growth appears to afford a wider “growth window” than is normally observed for c-plane growth. Different step flow surface morphologies with varying step widths were observed as a function of Ga:N ratio ans substrate temperature. Importantly, the miscut direction had a dramatic impact on morphology, suggesting strong anisotropy in gallium adatom diffusion barrier and resulting growth kinetics.
Growth and structure characterization of AlGaN/GaN superlattice on m-plane (10 0) GaN with various miscut direction
Jiayi Shao and Liang Tang
Recently nonpolar III/N devices (m-plane and a-plane) have attracted significant interest as there are no spontaneous or piezoelectric fields along these growth directions. Non-polar AlGaN/GaN superlattices may prove particularly useful for the design of complex intersubband-based optical devices in which polarization fields present a significant complication. In this project, we investigate heteroexpitaxial growth of AlGaN/GaN superlattices on m-plane GaN templates as a function of miscut direction and growth temperature under the metal rich growth conditions with a Ga-to-Nitrogen (Ga/N) ratio equal to 1.2. m-plane AlGaN/GaN growth is very sensitive to substrate temperature and miscut direction. We find that by closely controlling substrate temperature, superlattices exhibiting step-flow surface morphology and strong x-ray superlattice peaks can be grown with substrate miscut either towards the +c or –c direction.
