Thermodynamic study on compositional instability of InGaN/GaN and InGaN/InN during MBE

Thermodynamic analyses were carried out to understand influence of lattice constraint from GaN and InN substrates on relationship between solid composition x of InxGa1−xN films and input mole ratio RIn (=PIn0/(PIn0+PGa0) where Pi0 is the input partial pressure of element i) during molecular beam epitaxy. The calculated results suggest that compositional unstable region is found at small RIn region for InGaN on InN while that for InGaN on GaN can be seen at large RIn region at higher temperatures. This implies that InN-rich thin films are possible to form on InN substrate though it is difficult to form on GaN substrate.