Step-Flow Growth Model of N-polar GaN Metalorganic Vapor Phase Epitaxy

Abstract

  The Burton-Cabrera-Frank (BCF) theory has been applied to metalorganic vapor-phase epitaxy (MOVPE) of N-polar (0001) GaN. Owing to the hydrogen-rich atmosphere during MOVPE, surface N atoms of the N-polar (000-1) surface are mostly covered with H atoms. Extremely small coverage of the Ga adatoms competing with the H adatoms on the terraces can be calculated using the Langmuir adsorption isotherm. The equilibrium coverage of the Ga adatoms at steps and the equilibrium pressure of the NH₃ gas at step kinks can be calculated from the conditions of Gibbs energy balance between the sources (Ga adatom and NH₃ gas molecule) and the products (GaN and 3/2 H₂ gas molecules) and of speed balance between Ga and N incorporation into the step kinks. Growth rates of GaN on vicinal surfaces and hexagonal spiral pyramids has been calculated as a function of the trimethylgallium flow rate and compared with experimental results.