Ground state switching in InGaN/GaN quantum dot molecules

We present a detailed analysis of the electronic properties of In_0.25Ga_0.75N/GaN quantum dot (QD) molecules using an sp³ tight-binding model, including strain and built-in fields. The influence of the interdot separation is studied in detail. Our analysis reveals that, even if we assume two identical QDs, the molecular description of bonding and anti-bonding states breaks down for the single-particle states. This behavior originates from two effects, the strain field and the built-in potential. The strain field interactions between the two QDs suppress the ability to form bonding and anti-bonding hole states. Additionally, the built-in potential along the c-axis leads with increasing separation to a ground state switching between the two QDs. This is related to the behavior of the built-in potential in an isolated QD, where the potential drops back quickly toward zero, and may even change sign outside a strained c-plane QD.