Theoretical Investigation of Indium Surface Segregation in InGaN Thin Films

Surface segregation of In atoms in InGaN thin films on GaN(0001) substrate is investigated by using Monte Carlo simulations based on an empirical potential, which incorporates electrostatic energy due to bond charge and ionic charges. The calculated In composition of the surface monolayer (ML) xs in In0.1Ga0.9N thin films ranging from 1 to 31 ML predicts that In atoms segregate at the topmost layer even in the film thickness t being larger than 3 ML. The xs at the topmost layer saturates when t reaches ∼15 ML, in which xs is much larger (xs∼0.7) than the normal alloy composition (x ∼ 0.1). Furthermore, analysis of xs with respect to the bulk composition x up to 0.2 reveals that the propensity of In atoms for being segregated at the surface corresponds to the bond energy difference between InN and GaN. These calculated results imply that not only the release of elastic strains due to lattice mismatch between InN and GaN but also the preference of Ga-N bonds over In-N bonds in the bulk region contributes the segregation of In atoms at the surface in InGaN thin films. [DOI: 10.1380/ejssnt.2005.503]