Strain energy distribution in GaN and InGaN quantum dots on AlN buffer layers: A valenceforce-field approach

We have theoretically calculated the strain energy distribution in the GaN(dot)/GaN(wetting-layer)/AlN(buffer-layer) and In_0.2Ga_0.8N(dot)/ In_0.2Ga_0.8N(wetting-layer)/AlN(buffer-layer) structures using a valence-force-field method. The quantum dots (QD's) are modeled with 592 atoms assembled in a hexagonal shape. The GaN QD has practically no strain energy, while the GaN wetting layer has small strain (max.≈ 16 meV/atom). In contrast, the In_0.2Ga_0.8N QD has larger strain energy (max. ≈ 40 meV/atom) due to the alloy disorder effect. The In_0.2Ga_0.8N wetting layer is strained further. A possibility of the phase separation during the growth of InGaN QD's is discussed.