Introduction – why we made this book

The Acoustophotoelectric Effect: Efficient Phonon–Photon–Electron Coupling in Zero-Voltage-Biased 2D SnS2 for Broad-Band Photodetection

“…The enhancement in photocurrent at 285 and 365 nm can be attributed to the efficient transport of the photoexcited carriers since the photon energy is already deeper within the conduction band region, thereby permitting a direct radiative transition to occur. For longer wavelength excitation and in contrast to direct semiconductors, additional phonons are required for conservation of energy and crystal momentum in indirect semiconductors; as such, indirect semiconductors usually require larger momentum transfer to effect indirect transitions. ,, Since such transitions involve a two-step process and are strongly dependent on the phonon density of states, the rate at which these transitions occur are typically much slower than those for direct transitions . Nevertheless, we see from Figure b that even though the photon energy at 565 nm is below that for a direct (Γ–Γ) radiative transition, a detailed analysis of the band structure shows that direct radiative transition is possible along the Γ–M path of the Brillouin zone due to the effect of the SAW in lowering the band gap of the SnS 2 thin film from 2.32 down to 1.35 eV.…”