Hi all, :
We are looking to grow Cadmium Sulfide with the humid technique of Chemical Bath Deposition (QBD),
It has n't been difficult to achieve thicknesses of about 200 nm with good adherence and uniform deposition, i.e. good expected results
But now, we need thin films of a few micrometers. From what I have read, is not straightforward to achieve more than 500 nm - 800 nm with this technique.
Does anyone have achieved these levels of thicknesses using this technique ?
Of course, if is possible to do it, the alternatives could be, either to conduct several baths in series on the same sample,
or to experiment with longer deposition times, i.e. 10-12 hrs
(or a combination of both ideas)
But I think the long deposition times idea isn't the most recommendable one.
btw, the precursors I am using are: CdCl2, Na3C6H5O7, KOH and CH4N2S
I'll appreciate any help !
Regards !
Hello Hernandez,
Chemical bath deposition method is sometimes deceiving. Different deposition parameters play crucial role in determining the thickness as well as the physical properties of the deposited film.
Yes, it possible to deposit a film having thickness in the range of 2-3 micrometers. In that case you need to use higher molar concentration of the precursors of both the positive (Cd) and negative (S) ions.
In my case, while depositing ZnSe thin film on glass substrate by CBD technique, I used 0.5 M Zinc acetate dihydrate slution and proportionate Se precursors (refluxing Se powder and Na2SO3), and obtained a film with 2.059 micrometer thickness, measured by FESEM, by a 2 hour deposition.
I am not sure whether longer deposition time (10-12 hours) would help to increase the thickness, since bulk amount of the product of the reactants in the chemical bath precipitate and does not take part in film synthesis.
In summary, you can try to increase the molar concentration of the ions precursors to achieve thicker CdS films. You can also increase the thickness by redepositing the films by using multiple deposition. Again, since the film deposition in CBD happens in alkali medium (generally, pH>10), you got to check the pH of the solution frequently as ammonium hydroxide, commonly used as pH leveler, evaporates fast due to the temperature of the bath.
These is a huge body of research related to CBD deposited CdS film. You may search it in the google scholar by putting "CdS + Chemical bath deposition".
You can also read the book written by Gary Hodes to know the intricate details about CBD technique.
Hope this helps!
Dear Bazlul Karim :
The information in your reply is very useful,
Thank You, I have n't had though about the points you mentioned, however all you say make sense.
Just to be be clear; when you say "since bulk amount of the product of the reactants in the chemical bath precipitate and does take part in film synthesis" you mean that the already deposited film of the material might precipitate back to the solution during the course of the Bath... Am I right?
I'm thinking I'm gonna try first the methodology of conducting more than one Bath on the same substrate to see if with 3 or 4 consecutives Baths I can increase the thickness of my final film without seeing an appreciable detachment of the film, so I don't need to change the formulation(recipe) for the Bath.
Thank you !
Hi Hernandez,
In CBD, film deposition happens by dual procedures, ion-by-ion deposition or cluster by cluster deposition or both of them together. Again, deposition of film depends on the solubility product of the film, CdS in your case. If the solubility product for particular specimen (which you want to synthesize) is low, then even low concentration of precursors end up depositing the film. However, the downside of this low solubility product is that higher concentration of the precursors produce the final product very fast and they precipitate, failing to take part in film formation.
I meant this particular phenomena where a significant portion of the precursors or ions may deplete from the solution via the aforementioned procedure which can not contribute to the film growth. To avoid this situation complexing agent(s) are added to the solution to slowdown the release of the positive/negative ions in the solution.
On the other hand, I am entirely not sure about the desorption of the film, where deposited film is pulled back to the solution. It's a reverse process indeed. But keeping the substrate long in the bath could have negative effect on the film thickness or property. But there is quite a large literature where people studied the effect of duration of film deposition on different properties of the materials.
I think you can get in depth understanding of these things if you go through the book on chemical bath deposition written by Gary Hodes. Try to search it in google and if are lucky enough you may get the PDF version.
Best of Luck!
I would like to thank Mr. Karim for his informative and useful answer.
I would like to point out that the reversibility of the reaction plays a great role in the ultimate thickness achieved by the CBD. As the starting concentrations increases the etch back rate will balance the deposition rate at a deposited film thickness.
I agree with Franklin that when one refresh the bath one can can achieve higher thickness.
Best wishes
Thank You A. Zerky, Thank you B. Karim,
I will try to follow these approaches
Regads ! :)
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