Dear Cyril,

I'm not working in special with these materials, but I think you have just see the emission of the alumina in the range of 400-500 nm. For amorphous alumina you have bandgap of ~ 2.6-2.9 eV, which fits very well your spectrum range.

Hope this will help a bit.

Dear Cyril,

The left peak is due to the ZnO. It became greater most probable because of the aluminum oxide passivation effect which reduces the recombination centers at the surface of ZnO. The broad band emission is due to fine grained or amorphous material with no sharp band edges. the sharp peak is due to band band emission.

This insight may help interpreting the results. But detailed interpretation requires to obtain the energy band structure. I think the layer which absorbs the incident radiation is ZnO and aluminum oxide is a wide gap material so the excess charges will be produced in ZnO which will be the active layer and the Z0 is just a passivator for it.

After searching for the bandgap of ZnO i found it = 3.6 eV while that for Al2O3 is about 7 eV . So, what i said is okay.

The window layer is the Al2O3

The active layer is ZnO,

So the ZnO is radiating layer.

This behavior because ZnO is very fine grained.

Best wishes

What is your excitation source and wavelength??

excitation lambda = 325 nm and this is the instrument we used PL spectrometer Fluorolog-3 / Horibo Jobin Yvon (Japan)..

Do you have a spectrum of Si substrate on its own?

yes. First we calculate the excitation wavelength from the UV-Vis spectroscopy for ZnO.

Welcome Cyril,

Your structure is Al2O3/ ZnO /Si . The aluminum oxide works as a window and will not absorb such exciting radiation, it will be absorbed in ZnO and then silicon. If the thickness of the ZnO is sufficient to absorb the incident radiation, then all he incident radiation will be absorbed in ZnO. If a fraction is transmitted then it will be absorbed directly in the surface layer of silicon. Silicon is indirect band gap and emits weak radiation in near infrared of about 1.1 um. Consequently the observed radiation is because of the ZnO photogenearted carrier. If ZnO was single crystal you would observe radiation mainly at the left peak according to band band radiative recombination. Because the material is very fine grained structure there will be high density allowed electronic sates near the condcution band and the valence band with minimum sate density at the mid band. So, there will be also radiation at photon energy less than the energy gap.

Best wishes.

Best wishes

Thank you sir for your answer. I am learning the spectroscopy part. I am understanding it slowly.

@Prof Zekry: Yes in the structure Al2O3/ZnO/Si, Al2O3 is coated just in the middle. And the other four sides of ZnO/Si are covered using a Cu mask while depositing Al2O3. And Al2O3 acts as dielectric gate oxide for my device.

Did you measure the Si on its own? I'm pretty sure this is the peak at ~380nm - so you should ignore this and concentrate on differences in the spectrum >410nm

I did not measure for Si alone.

It would be good if you could

Ok i will do it