An atomistic mechanism study of GaN step-flow growth in vicinal m-plane orientations. Issue 42 (12th October 2016)

• Record Type: Journal Article
• Authors: Liu, Zhun; Wang, Ru-Zhi; Zapol, Peter
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 42(2016)
• Page Start: 29239
• Page End: 29248
• Publication Date: 2016-10-12
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp04479d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : A DFT study of GaN step-flow growth in m -plane vicinal step orientations with variation of the chemical potential. 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 Ga and the excess chemical potential Δ μ, 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.