Imagine a donor/acceptor photovoltaic system with similar absorption coefficients at a particular wavelength. If you do a excite this system at this wavelength how do we describe the primary photoevent ?
Are you talking about excitonic transport, or resonant energy transfer, or some similar thing? When you ask about how to describe the primary photoevent, people usually start by separating it into strong, intermediate, weak coupling situations, although often the "correct" description depends more on the measurement you're making than the system itself.
Dear Sai,
The energy band structure dictates the type of transition of the photogenerated electron from the valence band to the conduction band leaving a free hole at the same time in the valence band. The phtogeneration occurs always in pairs of electron- hole.
In direct band material the e-h generation process do not need the assistance of phonons and consequently the probability of transition is relatively high. On the other side if the material is indirect band gap material where the bottom of conduction band and t he top of the valence band differs in momentum, the transfer of electrons from the the top of the valence band to the bottom of the conduction band needs a phonon in addition to the photon. Therefore, the probability of this transition is smaller than that of the direct band gap. Consequently, the photo absorption coefficient of the direct band gap material is greater than that of the indirect band gap material especially near the cut off wavelength.
I hope that fulfills your requirement.
wish you success.
- Badges
- Science topic