I want to know the type of the semiconductor from its band structure. Is it true if I claim the semiconductor is p-type when the fermi level energy goes to near HOMO, or n-type when the fermi level energy goes to near LUMO? Or we need other way in order to claim the type of the semicondutor.
Pls. find the explanation:
[A]The Fermi level E(F) is chemical potential for electrons. It is the energy level at which the probability of electron occupancy is 50%.{ Pls.look at the MIDDLE Figure of attached file to see position of Fermi Level{Ef}
[B] We know that adding Group 15th group elements ( Say Phosphorus dopant) to the group 14th group semiconductors[SC]( Silicon) produce n-type SC . With 5 electrons , now each silicon atom of SC has one extra electon on. They first reach the Fermi Level lying in middle; raise its energy so that it goes close to conduction band of n-type SC energetically( Electron donor levels).[ Pls llok at the RHS of the Figure
[C] Now adding Group 13th group elements ( Say Boron dopant) to the group 14th semiconductors[SC]( Silicon) produce p-type SC . With 3 electrons on B, now each silicon atom of SC has one electon deficient .i.e. positive hole. They first reach the Fermi Level lying in middle; lower its energy so that it goes closer to valence band ( Electron acceptor levels) of p-type SC [Pls. look at the LHS of the Figure].
[D] Now the frontier electronic structure of solids characterized by valence and conduction bands, which are analogous to the HOMO and LUMO of molecules built from MO theory.
[E] Combining[ B, C, D]. in n-type SC, the Fermi level is near in energy to CONDUCTION BAND band which ia analogous to LUMO while in p-type SC th Fermi level is near in energy to VALENCE BAND which ia analogous to HOMO.
I think we mainly use HUMO and LUMO in organic material system, for it is a collective result of calculation molecular orbital, while in inorganic material, band structure theory might be more commonly used where you have conduction band and valence band. In organic material it is not so easy to judge, because when some materials appear to be p-type due to the trapping of electrons.
[A]Though I don’t deny your right to have a different opinion, but will, humbly, request your good self to kindly relook into the word ANALOGOUS qualified twice before HUMO as well as LUMO in the my above given answer as:
“the Fermi level is near in energy to CONDUCTION BAND band which ia analogous to LUMO while in p-type SC th Fermi level is near in energy to VALENCE BAND which ia analogous to HOMO.
{B} Yet an other point - I, very humbly, bring to kind perusal is that terms HOMO and LUMO are also commonly used in complexes. Yes ;they have their origin in organic compounds for obvious reasons.
usully the band gap does not give the type of doping, it is possible to test the hot spot but the best is to study the Hall effect
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Semiconductor