I am working on linear and nonlinear properties of semiconducting thin films. I found that a huge nonlinear optical response (absorption coefficient, nonlinear refractive index) by these nanofilms. However, there were no significant changes in linear optical properties such as band gap, absorption coefficient. How can one attribute these observed results
Dear Sandeep Kannaiah
Have a nice time and good day
The appended articles study the linear and non linear optical properties of thin films. They may help you in you investigations.
Good luck
https://www.researchgate.net/publication/294426798_Studies_on_dielectric_properties_opto-electrical_parameters_and_electronic_polarizability_of_thermally_evaporated_amorphous_Cd50S50-xSex_thin_films
https://www.researchgate.net/publication/281495242_Influence_of_composition_on_optical_and_dispersion_parameters_of_thermally_evaporated_non-crystalline_Cd50_S50-xSex_thin_films
https://www.researchgate.net/publication/304150361_Study_of_optical_properties_of_thermally_evaporated_ZnSe_thin_films_annealed_at_different_pulsed_laser_powers
Article Studies on dielectric properties, opto-electrical parameters...
Article Influence of composition on optical and dispersion parameter...
Article Study of optical properties of thermally evaporated ZnSe thi...
I have some experience in working with ultra thin (100) silicon thin films. The type we used was Czochralski silicon. we fabricated 30micrometer and 70 micrometer thin films in our lab. We have accounted lot of defects while fabrication. But in general the most concerning defect was surface of the material and quality of the material when it comes into taking account of absorption coefficient. You can see the photon generation by spontaneous emission in silicon may be you can get the thing you are searching for.
Sandeep,
To be more useful, you question must be specific. Which means that you have o specify the property of interest to you. I read your question carefully and noticed that you mentioned the absorption coefficient in the linear and nonlinear properties!.
The band gap energy is a property of the atoms in material. It depends on the atomic arrangement of the in the materials that is the grain size. It depends also on the temperature of the material. It is required to define what is meant by linear and nonlinear properties. For example, the conductivity of the material varies linearly with the carrier concentration and mobility While it changes non linearly with temperature.
The absorption coefficient varies non linearly with the incident light wavelength.However, it may vary linearly with the film thickness.
Wish you success
Thank You for all your answers.
Dear Abdelhalim Zekry thank you for your suggestions. To be more specific, I have observed a small redshift in band gap of ZnO film upon doping different dopnats. Also, other optical parameters like absorption spectrum have also shown smaller variations. However, the nonlinear properties (using open aperture Z-scan experiment) showed huge variations such as switching from reverse saturable absorption to saturable absorption. My question is how to interpret this observed phenomenon.
Do you mean that undoped ZnO has an absorption coefficient which goes down with intensity? And doping the ZnO heavily with donors (n-type) resulted in an absorption coefficient which goes up with intensity?
Maybe look into "free carrier absorption". Perhaps free electrons in the ZnO conduction band have a high two photon absorption coefficient.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science