I have designed a nanostructure having group 13 atom but when I doped with group 12 and group 14 atom energy gap changes dramatically. The energy gap values (Eg) are the order of group 13 pure nanostructure > group 14 atom doped nanostructure > group 12 atom doped nanostructure. How can I explain this?
dear Amarjyoti Das
Just to make me understand your problem... you say you have prepared base nanostructures with a group 13 element, for example Al or In nanoparticles or nano-something. If so, no gap would arise, because of the metallic character of your nanostructures. Therefore I suppose you have made a 13th group Metal Oxide nanostructure, which may be a semiconductor as in the InOx case (of course this is just a possible example, the same holding for other semiconducting metal compounds).
Then you have doped your base nanostructure. Doping refers to the addition of a very low atom % of a foreign species, at most of few % unit but mostly well below 1%. In this case you are creating defects in some locations of the base matrix. Such defects locally introduce energy levels or bands for charge carriers within the original base Gap, so that it appears (after a conduction measurement) as the Gap is narrowed. The different behaviour of group 12 and 14 dopants possibly relies to the different atomic volume offered by the two cases, but a chemical contribution could not be excluded. There is no unique recipe that explain the exact behaviour you observe. The real systems under study should be known.
All above is an indicative answer that holds in case of "doping". All the stuff may deeply change if the amount of 12th or 14th group components is much larger than what is universally know as "doping".
You can start off by looking at the changes in strain moduli, which affect the acoustic and optical vibrations due to the doping. A dopant modifies the crystal structure in such a way that energy coupling profile changes. Bandgap is the result of forbidden energies as oscillations cross over from acoustic into the optical.
dear Amarjyoti Das
Just to make me understand your problem... you say you have prepared base nanostructures with a group 13 element, for example Al or In nanoparticles or nano-something. If so, no gap would arise, because of the metallic character of your nanostructures. Therefore I suppose you have made a 13th group Metal Oxide nanostructure, which may be a semiconductor as in the InOx case (of course this is just a possible example, the same holding for other semiconducting metal compounds).
Then you have doped your base nanostructure. Doping refers to the addition of a very low atom % of a foreign species, at most of few % unit but mostly well below 1%. In this case you are creating defects in some locations of the base matrix. Such defects locally introduce energy levels or bands for charge carriers within the original base Gap, so that it appears (after a conduction measurement) as the Gap is narrowed. The different behaviour of group 12 and 14 dopants possibly relies to the different atomic volume offered by the two cases, but a chemical contribution could not be excluded. There is no unique recipe that explain the exact behaviour you observe. The real systems under study should be known.
All above is an indicative answer that holds in case of "doping". All the stuff may deeply change if the amount of 12th or 14th group components is much larger than what is universally know as "doping".
Dear Amarjyoti Das
There are two ways to look to ''doping'':
- If you introduce foreign atoms at ''high concentrations'' say >1% then it is not ''doping'' but a kind of ''alloying'' the foreign atoms are to behave as intrinsic atoms of the material host. In this case, it is natural that the energy bandgap may change drastically since the nature of the initial material has changed through alloying. This holds for bulk materials as well as for nanomaterials.
- If you introduce foreign atoms at ''very low concentraions'' say less than 0.000001 then it is really doping i.e. foreign atoms are to behave as ''donors'' or ''acceptors'' in the original matrix material which becomes n-type or p-type but with otherwise ''unchanged properties''. This is valid for bulk materials.
However, here, in the case of nanostructured materials (e.g. with nanograins or nanocrystallites at the nanosize) even ''doping'' can induce huge changes in the morphology of the layer (overall form and size of the nanograins) as well as in its structural properties (crystal properties and growth axis orientation). In this case, these may induce huge effects on energy bandgap (size, structural and broadening effects).
See (e.g.) the following paper :
Article Translucent Thin Film Fe 2 O 3 Photoanodes for Efficient Wat...
Best regards,
Prof. A. Kadri
Dear Amarjyoti Das
The following book can provide you with a fundamental mechanism of alteration of the bandgap with the doping process.
Regards
It is quite obvious that Energy gap will be decreased if it is doped due to the appearance of donor (14 atom) and accpetor (12 atom) energy level below the conduction band and above the valance band of the semiconductor respectively which in turns reduces the energy gap as compared to the intrinsic semiconductor.
Thanks @ Gourab Das . But my question is - The energy gap values (Eg) are the order of group 13 pure nanostructure > group 14 atom doped nanostructure > group 12 atom doped nanostructure. How can I explain this?
dear Amarjyoti Das ,
all the collegues are trying to give you an answer or at least some ideas for a deeper analysis. However, if you wish to have some more specific answers, you should disclose more information about your real system:
- what is the base structure (material, nanostructure type),
' what are the dopants you have used, and their atomic percentage
- what doping process you have used (e.g. chemical post-processing, doping during main synthesis, or others)
' what are the Eg values you have measured and with which technique
With the above information, some could possibly provide you with a more complete and precise answer.
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