Can anyone explain the role of optical phonons theory with respect to quantum dot-based photo-detectors?
I could not understand certain characteristics such as GaAs (TO, LO modes, Interface frequency), quantum dot (TO, LO modes), etc. How are they related to the phenomena of photodetection (or say scattering not sure, I go by the name Raman Scattering ) or let us say how we expect a long wavelength operation of these devices?
(GaAs - Gallium Arsenide)
Dear Saranya,
Raman spectroscopy is a useful tool to investigate the vibration spectrum of solids (or liquids). Due to the interaction of the electric field of the light wave with the lattice, you absorb or emit additional phonons whereas electron hole pairs are generated. So, you have hv = Eg +- E phonon with Eg the gap energy. This is valid for direct gap semiconductor. For indirect materials you must carefully take into account the momentum conservation. Momentum conservation determines which phonons take part in the absorbtion (emission). The quantum dot in essentially changes the gap energy (evt. the phonon spectrum ).
Photo detectors work by excitation of electron hole pairs over the gap and their separation in an electric field. The energy needed for excitation is enhanced by the phonon energy. The gap energy is enhanced by the reduction of the size of nano particles. Therefore in the sum we have an enhancement of photon energy.
If you want to decrease the energy, nanostructuring seems to be the wrong way.
With Regards
R. mitdank
Thanks Mr. Rudiger.
But I want to understand the effect of strain on the phonon frequencies in Indium arsenide/ GaAs quantum dots system.
Of course, strain effects the elastic constants and therefore the phonon energies. I attach a paper I found concerning this problem.
R. Mitdank
Thanks Mr. Rudiger for sharing the paper.
I will have a glance at it and get back to you for further discussion. Hope it might help clear my doubts.
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