Dear Fiheon,

Please mention the exact material. Even the same material, say Cu2O shows carrier density from 1013 to 1017 cm-3 with respect to deposition method and parameters used. 

Unless there is doping or defects, the intrinsic carrier concentration is always less whether organic, inorganic or hybrid semiconductor.

I found the below paper (link provided) on an organic semiconductor "p-type doped organic semiconductor 2,7-bis(9-carbazolyl)-9,9-spirobifluorene", which possesses 1018 cm-3 carrier density.

This indicates that sufficiently higher carrier density can be obtained for organic semiconductors.

Best,

Chandan

http://aip.scitation.org/doi/abs/10.1063/1.3427416?journalCode=apl

Dear Chandan,

I was asking about undoped polymeric semiconductors like P3HT, PBTTT etc or small molecules typically acenes. Usually if someone working in the conventional silicon or GaN techonology would be eager to know that what is the typical intrinsic thermally generated carrier concentration at room temperature in these amorphous materials compared to silicon i.e, ni=10^11 /cm^3. So can we comment on the typical order at room temp in undoped organic semiconductors ?

Dear Fiheon,

welcome!

I treated such question before and this was my answer:

Now we continue the discussion; this time about the mobile carrier concentrations and their sources in the materials.

Generally in any semiconductor their are two types of mobile charges, the electrons in the conduction band and the holes in the valence band,

If the material is pure and intrinsic the source of the electrons and holes will be the thermal generation of electron hole pairs. The concentration of the electrons will be equal to that of the holes n0=p0=ni. According to the mass action law, n0 p0= ni^2,

The intrinsic concentration ni^2= Nc Nv exp - Eg/kT, where Nv, Nc are the effective density of states , Eg is energy gap and T is the absolute temperature. This law is a general law and applicable for all semiconductors.

Organic semiconductor materials have relatively high energy gaps compared to the most common semiconductor metallic material, the silicon Si. The effective density of states according to the data in the litterateur are not much different from those of silicon, therefore the intrinsic concentration of the organic materials is very very small. Accordingly, organic materials approach the insulators rather than the semiconductors. In the sense, practically in their intrinsic state they behave as insulator.

As a matter of purity of the material metallic semiconductor are produced with high purity but the organic semiconductors are produced with less purity such they contain impurities leading to make them either p-type or n-type conducting.

Once doped either intentionally or unintentional one one can define for them a Fermi level as the in the metallic material. Otherwise one describes them as insulators in the sense their energy levels are aligned to the vacuum level. If the material is doped the energy level through a system of materials is aligned to Fermi level at thermal equilibrium. This is a very important point and i investigated it intensively in the literature and discussed it in a separate post in the researchgate:https://www.researchgate.net/post/How_is_the_current_limited_in_metal_organic_semiconductor_metal_MOSM_diode

The doping of the metallic semiconductors is by atomic substitution while in the organic material it is by adding doping molecules. There is donor molecules and acceptor ones.

Both materials react to the incident light with the proper wavelength  by generating excitons in the materials. The excitons dissociate directly after their generation because of the larger screening between the their electrons and holes as the dielectric constant of the metallic semiconductors are much larger than those of organic materials. So, can speaks of photogeneration of electron hole pairs.

In contrary, the excitons are strongly bound in organic materials and need assistance to be dissociated before they recombine again. This assistance by an electric field or by donor acceptor interfacing.

Electrons and holes can be injected by forming junctions with different materials, This is valid for both type of materials.

This concerns the mobile charge carriers and their main sources in the both classes of materials.

It is required to compare organic and inorganic semiconductors?. Available from: https://www.researchgate.net/post/It_is_required_to_compare_organic_and_inorganic_semiconductors [accessed Aug 6, 2017].

Best wishes

104-105 cm-3 in polymer semiconductors