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 In _x Ga _1-x N films and input mole ratio R _In (=P _In ⁰ /(P _In ⁰ +P _Ga ⁰ ) where P _i ⁰ is the input partial pressure of element i) during molecular beam epitaxy. The calculated results suggest that compositional unstable region is found at small R _In region for InGaN on InN while that for InGaN on GaN can be seen at large R _In 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.