I have obtained Al doped ZnO films by spray pyrolysis. Crystalline quality of the samples became worse with increasing Al doping rate(especially after 6%).
I will test this effect by reproducing the samples. Can anyone comment on the possible mechanisms those can cause a dissociation like this?
Al doping especially for the case of ZnO thin films has been studied vastly owing to interesting behaviors. It has been proved that Al would deteriorate the crystallinity for several reasons. There is always a tendency for the aluminum dopants to segregate at the grain/inter particle boundaries even for a low doping concentration. To get more data I'd refer you to this paper:
B. Nasr, S. Dasgupta, D. Wang, N. Mechau, R. Kruk, H. Hahn, J. Appl. Phys. 108
(2010) 103721.
In spray pyrolysis one would increase the spray rate that should be optimized with the carrier gas and other parameters.The dopants are usually mixed in the precursor solution and sprayed. If you mean that the Al incorporation is greater than 6% in the precursor solution, then the actual % of Al incorporation may be different in the film due to various effects. However, excellent TCO's prepared using spray pyrolysis have been reported by many groups. The decrease in crystallinity may be associated with insufficient temperature, excessive volume of liquid sprayed at a given time, pH etc. It has been proved that Al would deteriorate the crystallinity for several reasons. segregation at the grain/inter particle boundaries is ine of the reasons.
https://www.researchgate.net/publication/235987629_Optical_properties_of_zinc_oxide_thin_films_doped_with_aluminum_and_lithium?ev=prf_pub
https://www.researchgate.net/publication/235987620_Tailoring_the_optical_properties_of_Mg_(x)_Zn1-x_O_thin_films_by_nitrogen_doping?ev=prf_pub
Dear Serhat,
depends what you understand by crystalline quality. Anyway, after a certain concentration of Aluminium, as Ali wrote, the seggregation of Al2O3 ocurrs. Take care also of Gahnite Phase. Up there are links for 2 papers which moght be of your help.
Article Optical properties of zinc oxide thin films doped with alumi...
Article Tailoring the optical properties of Mg (x) Zn1-x O thin film...
thank you for your answers. I will try to deposit the samples by changing the experimental parameters.
There is a certain solubility of impurity atoms in semiconductor materials. In the case of A2B6 semiconductors, which also include zinc oxide solubility of Al is not more than 0.1%. You use 6%, and it is very much. In this case, as stated above, there will be a segregation of impurity atoms and the formation of other phases. Usually it will significantly degrade the crystalline quality of the films.
Even in an epitaxial film there will still be a deterioration of the quality due to formation of compensating defects under high doping concentrations. This may be a cause for deteroration crystalline quality as well. For ZnO:Ga, a high concentration of zinc vacancies (acceptors) may form. See: http://prb.aps.org/abstract/PRB/v84/i11/e115202
We worked on Al-doped ZnO films synthesized by sol gel method, doping level being 0-2 at%. We found decrease of grain size with increase of Al-doping upto a certain extent, but no degradation of crystalline quality was observed. Here is the reference: Mat. Chem. Phys. 74 (2002) 83-91
Suchitra Sen @ : Unfortunately I do not have access to the full text article. So I was able to read only the abstract. I have questions: (i) how controlled the actual concentration of aluminum atoms in ZnO films since you mentioned about possible Al segregation along the grain boundary (ii) how the aging effects and annealing of films affect on crystalline quality of ZnO films.
Yuriy Gnatenko, you can send me your email id. I can send you the full paper. You will get your answers in the paper.
Dear Suchitra Sen,
Here is my e-mail : [email protected]
Thank you.
Best regards,
Yuriy Gnatenko
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