Phono-voltaics, phonon harvesting and band gap tuning in nanoscale HgTe/CdTe and InAs/GaSb p–n heterojunctions: insights from ab-initio exploration

Abstract Phono-voltaics, a recently proposed mechanism, enables current generation in nanoscale p–n junctions by harvesting non-equilibrium optical phonons in place of optical illumination. In the phono-voltaic operational regime, electron–hole pairs are created through optical-phonon-mediated scattering, provided the phonon energy is resonant with or exceeds the band gap. In this work, by combining DFT, NEGF, and STD methods, we propose that topological HgTe/CdTe and InAs/GaSb p–n heterojunctions can be engineered to operate in either the phono-voltaic or photo-voltaic regime by tuning the number of HgTe (GaSb) atomic layers. This layer-dependent design enables band-gap tuning relative to the phonon energies, thereby controlling the operating regime. Our study further shows that in the photo-voltaic regime, electron–phonon coupling (EPC) significantly influences the photovoltaic parameters at room and higher temperatures, underscoring the necessity of including EPC in such calculations. We also demonstrate that the combined DFT + NEGF + STD framework provides reliable theoretical estimates of key phono-voltaic and photo-voltaic characteristics—including phono-current, photo-current, open-circuit voltage ( V OC ) , temperature-dependent band-gap shifts, and optical absorption—in nanoscale p–n junctions.