Question

What are two most well-known "Bands" in traditional or classic (inorganic) semiconductors? For most organic materials, scientists typically do not use those " Bands" and instead using different but similar names, what are those name, and explain the differences and similarities between organics verus inorganic semiconductors inters of thoses names

Answer 1

Answer:

The two most well known Bands in Inorganic semiconductors are: 1) Valence band 2) Conduction band

The term "bandgap" refers to the energy difference between the top of the valenceband and the bottom of the conduction band. Electrons are able to jump from one band to another.

The two bands in Organic Semiconductors are reffered as 1) HOMO (like valence band) 2) LUMO (like conduction band)

HOMO : Higest Occupied Molecular Orbital

LUMO: Lowest Occupied Molecular Orbital

Differences between Organic and Inorganic Semiconductors:

1) The fundamental difference between inorganic and organic semiconductors is in the charge transport mechanism.

In inorganic semiconductors charge transport can easily take place as a result of the strong covalent bonding between atoms in the lattice, which leads to a delocalization of the electronic states. Conversely, in organic semiconductors the bonding between molecules is due to the relatively weak van der Waals or London forces leading to a small overlap of the molecular orbitals which is not favorable for charge transport.

2) Organic semiconductors are made from carbon based materials, whereas inorganic semiconductors are made of noncarbon based materials such as silicon.

3) Another consequence is doping effect. In inorganic SC, atomic doping normally just increases carrier density and does not interfere the band structure. On the other hand, molecular doping in (weak Van der Waals interaction) organic SC affects the molecular packing and assembly, hence the morphology and electronic properties of the film such as mobility.

4) Organic semiconductors generally have much lower mobility (performance essentially) than inorganic Semiconductors.

Similarities between Organic and Inorganic Semiconductors:

It should be noted that there is not a 1-to-1 similarities

1) The HOMO energy level in Organic SC is like the valence band in the Inorganic SC

2) The LUMO energy level in Organic SC is like the conduction band in the Inorganic SC

3) The band gap energy difference between the HOMO and LUMO energy levels is similar to the band gap energy for intrinsic inorganic semiconductor literature