Nucleation of III nitride semiconductors in heteroepitaxy

The nucleation of III nitride semiconductors in heteroepitaxy is theoretically investigated using GaN nucleation on the AlN surface as an example. It is inferred that the mechanism of this process is determined by the temperature at the initial stage of the layer formation (T). At low temperatures (T<500°C), liquid gallium droplets appear and the chemical reaction between the Ga and N atoms results in the formation of GaN nuclei. At substrate temperatures T>650°C, there arise only GaN nuclei. It is revealed that the GaN nucleation is governed by the generalized diffusion coefficient of GaN, which is a combination of the diffusion coefficients for gallium and nitrogen atoms. It is shown that the generalized diffusion coefficient of GaN on the crystal surface increases by seven orders of magnitude as the growth temperature increases from 600 to 800°C. This is accompanied by a change in the growth mechanism of the III nitride semiconductor epitaxial layers.