Dimension-dependent hydrostatic strain and band-edge shifts in InN/GaN core–shell quantum dots

Introduction: Lattice mismatch at the heterointerface of a core–shell quantum dot (CSQD) architecture generates significant internal strain. The geometrical dimensions of the core and shell regions govern the strain distribution, which modifies the electronic band structure of the quantum dot. The indium nitride/gallium nitride (InN/GaN) CSQD system, possessing a substantial lattice mismatch of approximately 10%, serves as an ideal model for exploring these geometry-dependent band-edge modifications. Materials and methods: An analytical theoretical framework for a spherical InN/GaN CSQD is developed to calculate geometry-dependent hydrostatic strain and its effect on band-edge shifts. The analytical model utilizes the elastic continuum approximation and deformation-potential formalism. Assuming an idealized, coherent, and defect-free core–shell interface, dimension-dependent strain values, strain-induced band-edge shifts, and interface band offsets were calculated. The dimensional changes include systematically varying the InN core radius and GaN shell thickness between 4 nm and 6 nm. Results: The analytical calculations demonstrate that the InN core undergoes compressive hydrostatic strain, while the GaN shell experiences tensile hydrostatic strain. Increasing the core radius reduced the compressive strain in the core while enhancing the tensile strain in the shell, resulting in a decreased core and shell band-gap energy. In contrast, increasing the shell thickness subjected the core to greater compressive strain, which increased the core and shell band-gap energy. Across the investigated geometrical variations, the calculated core band-gap energy varies by approximately 13.4–13.9 meV, while the shell band-gap energy varies by approximately 23.8–24.8 meV. Despite these energy shifts, the system retains a stable Type-I band alignment, with the conduction band offset dominating approximately 75% of the total discontinuity. Conclusions: The findings establish a predictable correlation between the structural geometry of InN/GaN CSQD, the hydrostatic strain, and its influence on band-edge positions. This study provides a theoretical framework for utilizing geometry-induced band-structure engineering, providing a basis for future investigations into the optoelectronic properties of strained III-nitride heterostructures.