Investigation of truncated conical quantum dot superlattice: effects of geometry on miniband formation and electronic transitions for intermediate-band solar cell

Superlattice structures (SL) formed by quantum dot layers offer significant potential to enhance the performance of optoelectronic devices. The limitations of traditional semiconductor devices can be overcome by introducing multiple energy bands, thereby enhancing photon absorption and charge-carrier dynamics. Based on a truncated conical quantum dot superlattice, which is a newly focused shape, the electronic transitions in an InGaN/GaN quantum dot superlattice (QDSL) are investigated, focusing on valence band (VB) to intermediate band (IB) and IB to conduction band (CB) transitions that enhance sub-bandgap absorption and photocurrent generation. The interband transition energies among VB, IB, and CB lie within the range of 280 to 1340 meV. Using the effective mass approximation and the Kronig-Penney model, the time-independent Schrödinger equation is solved in three dimensions. The calculated ground state and excited state energies are E0=1.644 eV, E1=2.2035 eV, and E2=2.519 eV for a structure of 4 × 4 QD layers. Additionally, the spatial behavior of electron wave functions as a function of interdot spacing, from bottom to top between the QDs, is also examined. The electric potential profile along the vertical axis between two QDs and across a 4 × 4 array of QDs is analyzed using an analytical model, providing insight into confinement and interdot coupling within the superlattice. These findings provide valuable insights for the development of advanced next-generation quantum dot intermediate-band solar cell (QD-IBSC) technologies.