An atomistic mechanism study of GaN step-flow growth in vicinal m-plane orientations

Abstract

Elucidation of homoepitaxial growth mechanisms on vicinal non-polar surfaces of GaN is highly important for gaining an understanding of and control thin film surface morphology and properties. Using first-principles calculations, we study the step-flow growth in m-plane GaN based on atomic row nucleation and kink propagation kinetics. Ga-N dimer adsorption onto the m-plane is energetically more favorable than that of Ga and N isolated adatoms. Therefore, we have treated the dimers as the dominant growth species attached to the step edges. By calculating the free energies of sequentially attached Ga-N dimers, we have elucidated that the a-step edge kink growth proceeds by parallel attachment rather than by across the step edge approach. We found a series of favorable configurations of kink propagation and calculated the free energy and nucleation barriers for kink evolution on five types of step edges (a, +c, -c, +a + c, and -a - c). By changing the chemical potential μ and the excess chemical potential Δμ, the growth velocities at the five types of edges are controlled by the corresponding kink pair nucleation barrier E* in their free energy profiles. To explore the kink-flow growth instability observed at different Ga/N flux ratios, calculations of kink pairs on the incompact -c and +c-step edges are further performed to study their formation energies. Variations of these step edge morphologies with a tuned chemical environment are consistent with previous experimental observations, including stable diagonal ±a ± c-direction steps. Our work provides a first-principles approach to explore step growth and surface morphology of the vicinal m-plane GaN, which is applicable to analyze and control the step-flow growth of other binary thin films.

Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

“…Therefore, we propose an alternative atomistic mechanism for the growth instability of high Al-composition m-plane AlGaN. Our model builds on the results of Liu et al 26 for firstprinciple calculations of step-flow homoepitaxial growth of m-plane GaN. Liu et al emphasized that the energetics of atomic row nucleation and kink propagation at different types of step-edges are more important for predicting m-plane growth than single adatom surface mobility.…”

“…Liu et al emphasized that the energetics of atomic row nucleation and kink propagation at different types of step-edges are more important for predicting m-plane growth than single adatom surface mobility. 26 They also found that Ga-N dimers are more stable than isolated Ga and N adatoms, and the main feeding species for m-plane GaN growth. 26 Therefore, for AlGaN growth, we conclude that Al-N dimers should also be more stable than isolated Al and N atoms, and more stable than Ga-N dimers.…”

“…26 They also found that Ga-N dimers are more stable than isolated Ga and N adatoms, and the main feeding species for m-plane GaN growth. 26 Therefore, for AlGaN growth, we conclude that Al-N dimers should also be more stable than isolated Al and N atoms, and more stable than Ga-N dimers. Our proposed mechanism, shown schematically in Fig.…”

Structural Modulation of GaN Nanowires Grown in High-Density Plasma Environment

“…We have made many efforts to explore the resolution of these challenges. In our previous works, we explored nonammonia methods to prepare and modulate GaN NWs with the reduction of hydrogen and activated carbon by PECVD. ,, Under the plasma-phase conditions, changing the state of the plasma in the chamber is proved to be of great help for modulating the structure of GaN NWs. ,, The plasma-phase growth environment is proved to be a potential way to modulate the structure of 1D materials widely, greenly, and rapidly …”