Dear all:
Have anyone deposited Al contacts on substrates of CdS and/or PbS, using an e-beam physical evaporation system ?
The following is happening with my CdS and PbS films ,
I'm trying to deposit a good quality Aluminum electric contacts with an e-beam evaporator, on the top of chemical bath deposited CdS and PbS thin films...
In both cases I'm trying to grow a deposit of 200 nm or 300 nm of Al. But when I run the deposits on the CdS films, the Al deposited above de CdS looks with a 'regular' quality, however sometimes I get a silvery uniform finish of the contacts.
But when I try to do the same on the PbS thin films, I always finish with a deposits with a somewhat white aspect, meaning that Al2O3 is growing on there, but this doesn't happen with the CdS films ...
Anyone has experimented something like it ?
Do you think the roughness of the films may be having an impact on whether pure-Al or a mix of Al and Al2O3 is growing on the e-beam deposited films ?
I am doing both deposits (Al on CdS and Al on PbS) with exactly the same conditions (i.e. current, grow rate, temperature and vacuum pressure).
Do you think it could be a matter of the surface of the susbtrate ? .. this would be unexpected, since I am growing 300 nm of Al... is not 10 nm, so the substrate should n't have an impact on the morphology of the above deposited thin film, and not to say an impact on the chemical composition of the surface of the films (Al films).
I hope someone can give me any help
Kind Regards !
Dear Thomas Breuer
:Thank you for replying, Yes, I did compre the electric resistance of my several electric contacts. And indeed, those films with the whitish appearance have greater electric resistance, in opposition with those which the deposits looks metal silvery, (on my CdS' subtrates). Also this is consistent with the hypothesis that I'am getting mostly Al2O3 at the surface in my PbS/Al samples, in comparison with those CdS/Al samples. Also we performed a chemical analysis of the surface, and certaintly we see a lot of Al2O3 and very little of metallic Al, spekaing about the PbS samples.
About the electric resistivity of the samples, the Al2O3 introduced by the e-beam deposition makes the samples to be much more resistive than those with the more metallic-aspect contacts.
I get your point Thomas: "Without any oxygen in the chamber you cannot grow oxide layer of several hundred micrometers", but I think, even if we are doing the deposits starting with working pressures of 10-7, and ending with 10-6. I believe there still Oxygen always inside the chamber, I think this happens in every vacuum-system deposition technique. The sources of Oxygen can be; Oxygen which is present in the Al pellets (added there from the fabrication process), Oxygen which may be chemically attached on the surface of our samples, and may get gassified with the temperature of the process, or the tiny amount attached to the walls, which the pumps are not able to push out after ending the evacuation process.
But, yeah we are sure we are ending with an oxidized surface.
I haven't put attention to the base pressure of the chamber, also haven't perform a qualitative analysis on my CdS and PbS films ... Do you think in something specifically than can help me out doing this analysis to my samples ?
Thank you for your reply, I really need help,
btw, these experiments are n't for purposes of publication yet, at this point we are trying to test the concept.
Thank you, Best Regards !
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