Silicon wafer as substrate in Zinc oxide thin films

  • #1
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Good day, many articles used sillicon wafer as substrate over others (like:platinum, glass, sapphire and etc) to grow Zinc oxide thin films, but i'm don't know the real reason they choose silicon wafer as substrate compare to others. so i'm asking what are the advantages of using Silicon wafers as substrates? thanks in advance.
 

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  • #2
f95toli
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My guess is that it is because silicon is by far the most common substrate for all types of processing. Basically, unless there is a good reason not to use it (e.g. because you are trying to grow an epitaxial film and there is a large lattice mismatch between Si and your material) it would be the first choice for most people. Good Si is cheap and readily available (with different resistivity etc) and usually OK to use in most research cleanrooms (many cleanrooms have strict rules against using some materials because of the risk of contamination) . There is a huge amount of knowledge when it comes to how to process it.
Another reason is that is -for obvious reasons- commercially important. A process/device that is compatible with silicon is much more likely to be of commercial interest since it means it can be integrated (and fabricated) with semiconductor components.
 
  • #3
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Thank
My guess is that it is because silicon is by far the most common substrate for all types of processing. Basically, unless there is a good reason not to use it (e.g. because you are trying to grow an epitaxial film and there is a large lattice mismatch between Si and your material) it would be the first choice for most people. Good Si is cheap and readily available (with different resistivity etc) and usually OK to use in most research cleanrooms (many cleanrooms have strict rules against using some materials because of the risk of contamination) . There is a huge amount of knowledge when it comes to how to process it.
Another reason is that is -for obvious reasons- commercially important. A process/device that is compatible with silicon is much more likely to be of commercial interest since it means it can be integrated (and fabricated) with semiconductor components.

thanks you!, but, i'm expecting an answer about its physical and chemical properties, but aside from that, what are the mechanism or how ZnO nucleates in Silicon substrate? or what other properties silicon possessed to be become compatible in growing Zinc oxide thin films?
 
  • #4
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My guess is that it is because silicon is by far the most common substrate for all types of processing. Basically, unless there is a good reason not to use it (e.g. because you are trying to grow an epitaxial film and there is a large lattice mismatch between Si and your material) it would be the first choice for most people. Good Si is cheap and readily available (with different resistivity etc) and usually OK to use in most research cleanrooms (many cleanrooms have strict rules against using some materials because of the risk of contamination) . There is a huge amount of knowledge when it comes to how to process it.
Another reason is that is -for obvious reasons- commercially important. A process/device that is compatible with silicon is much more likely to be of commercial interest since it means it can be integrated (and fabricated) with semiconductor components.

I think the answer may be found by answering the question, does Zinc Oxide diffused into Silicon under certain fabrication method (like spray pyrolysis)?,does silicon breaks down during nucleation of Zinc oxide?
 
  • #5
f95toli
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I am not at all an expert on ZnO (I am familiar with a bunch of other oxides), but a quick google Scholar search suggest that most people who try to grow epitaxial ZnO do so on R-cut sapphire and/or use a buffer to allow them to grow it on Si. Hence, any articles you've found where they grow ZnO directly on Si probably describes work where they don't need the ZnO to be epitaxial, in which case you can use (nearly) whatever substrate you want; in which case the reasons I outlined above come into play.
Also, note that there isn't in practice that many substrates to choose from. There is of course a bewildering number of material that could potentially be used a a substrate, but only a handful or so are available as high-quality reasonably large wafers (say larger than 5x5mm2). This is another reason why most people -regardless of what they are studying- end up using Si or sapphire.

To answer your second question: I would be very surprised of ZnO diffused into Si. AFAIK this only happens with certain metals (most notably gold). I would also be surprised if SI would break down, this would only happen at temperatures way higher than what would be used in any fabrication method I've ever encountered.
 
  • #6
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I am not at all an expert on ZnO (I am familiar with a bunch of other oxides), but a quick google Scholar search suggest that most people who try to grow epitaxial ZnO do so on R-cut sapphire and/or use a buffer to allow them to grow it on Si. Hence, any articles you've found where they grow ZnO directly on Si probably describes work where they don't need the ZnO to be epitaxial, in which case you can use (nearly) whatever substrate you want; in which case the reasons I outlined above come into play.
Also, note that there isn't in practice that many substrates to choose from. There is of course a bewildering number of material that could potentially be used a a substrate, but only a handful or so are available as high-quality reasonably large wafers (say larger than 5x5mm2). This is another reason why most people -regardless of what they are studying- end up using Si or sapphire.

To answer your second question: I would be very surprised of ZnO diffused into Si. AFAIK this only happens with certain metals (most notably gold). I would also be surprised if SI would break down, this would only happen at temperatures way higher than what would be used in any fabrication method I've ever encountered.

How about the adsorption properties of silicon, and how bout the surface free energy needed to nucleates an oxide layer?
 
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  • #7
f95toli
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How about the adsorption properties of silicon, and how bout the surface free energy needed to nucleates an oxide layer?

I have no idea.
However, I suspect those properties are more or less irrelevant since the lattice mismatch between Si and ZnO is so large that you can't have epitaxial growth anyway. This would be a much bigger problem for high quality film growth than the those properties, especially since adsorbtion rate etc. be changed by altering the growth conditions (substrate temperature etc) which in turn affects the growth mode of the film.
 
  • #8
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I have no idea.
However, I suspect those properties are more or less irrelevant since the lattice mismatch between Si and ZnO is so large that you can't have epitaxial growth anyway. This would be a much bigger problem for high quality film growth than the those properties, especially since adsorbtion rate etc. be changed by altering the growth conditions (substrate temperature etc) which in turn affects the growth mode of the film.

But what is the difference of using glass substrate over silicon substrate? i think the mismatch of crystal parameters would help not to diffuse zinc oxide on Si under a fabrication method but remain on the surface of the silicon.
 
  • #9
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lattice mismatch forces the deposit into a particular structure. the most energetically favorable structure will typically be that which matches the substrate, for example, if the 111 direction of film is a better match to the 100 of the substrate (assuming growth is taking place on the surface of 100) it will want to grow 111 instead of 100. unless you are trying to chemically change the substrate, you dont want much diffussion. diffussion rules are typically atomic, whereas lattice matching speaks to lattice systems and paramteters to get a particular structure (unless you just want to grow bulk, in which case the substrate is somewhat irrelevant depending on the sensitivity of yield).

zinc oxide from what i can tell wants to be wurtzite (a = 3.25 Å, c = 5.2 Å) , while silicon is diamond (5.431 A) and saphire is hexagonal R-3c (trigonal, (a=4.785, c=12.991). so i could see zinc oxide wanting to line up its long axis with that of silicon (depending on wykhoff positions) (5.2 is around 5.4), or sapphire (4.785 is around 5.2), but since wurtize is a bit closer in structure to trigonal than diamond, i would suggest using sapphire over silicon if you want 001 growth of zinc oxide on a 100 sapphire.

this article is old but gives a good idea of the obstacles of heterostructures. https://www.fkf.mpg.de/49636/kk140.pdf

apologies if this is all old news, and you were more interested in some other aspect of their differences in relation to the topic at hand
 

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