It is observed that resistivity decreases drastically on crystallization. Is it due to change in band gap or mobility or both?
Dear Dr. Maria,
You have mentioned that in amorphous semiconductors, Fermi level is within the band gap and at 0K there are no conduction electrons. This is same in case of crystalline semiconductors also as the Fermi level is almost in the middle of the band gap in intrinsic semiconductors. This does not explain the difference between crystalline and amorphous state of the same material. I think mobility of charge carriers decreases drastically in amorphous state due to absence of long range order. This is why conductivity is more in crystalline as compared to amorphous state of the same material. Am I right?
Dear Anjani
Electrical resistivity quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge.
Crystalline materials consist of a lattice of atoms, each with an outer shell of electrons which freely dissociate from their parent atoms and travel through the lattice. This 'sea' of dissociable electrons allows the metal to conduct electric current and the resistivity is low.Also, in crystalline materials, the Fermi level lies inside or just below the conduction band giving rise to free conduction electrons. However, in amorphous semiconductors the position of the Fermi level is within the band gap. This means that at 0 kelvin, there are no free conduction electrons and the resistance is infinite. However, the resistance will decrease if the charge carrier density in the conduction band increases via doping or crystalization of the material.
Dear Dr. Maria,
You have mentioned that in amorphous semiconductors, Fermi level is within the band gap and at 0K there are no conduction electrons. This is same in case of crystalline semiconductors also as the Fermi level is almost in the middle of the band gap in intrinsic semiconductors. This does not explain the difference between crystalline and amorphous state of the same material. I think mobility of charge carriers decreases drastically in amorphous state due to absence of long range order. This is why conductivity is more in crystalline as compared to amorphous state of the same material. Am I right?
Thanks Dr. Maria, In crystallization, mobility of amorphous semiconductors increases so resistance decreases as mentioned by Mr. Suresh but why ?
Dear Mr. Anjani low mobility is due to absence of long range order... as I have already mentioned above......
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