Dear Balkrishna Choubey,

We call graphene as semimetal instead of semiconductor. It has a 'metallic behavior' only at K point.

May this answer helps.

@Shibghatullah Muhammady, can we use this semimetal as semiconductor?

I agree to the Shibghatullah Muhammady point. Due to its mechanical properties, electronic properties, structural stability and zero band gap, graphene is known as a zero band gap semiconductor or semimetal. In order to make it as a semiconductor, you can change the structure by doping any transition metal atoms or by creating vacancies in the graphene structure so that the band gap of the graphene gets increased. Thus, it can possess the semiconductor electronic properties.

Assuming that the question has bearing on the property of graphene at charge neutrality, that is when the Fermi energy εF coincides with the energy of the Dirac points, the excitations are gapless and therefore spectroscopically the system is metallic. An interesting issue arises here: because of the linear dispersion of the energy bands at the Dirac points of graphene, the density of the electronic states D(ε) is vanishing at ε = εF, suggesting that the longitudinal electric conductivity σxx(ε) were similarly vanishing at ε = εF, signifying a non-metallic behaviour at ε = εF. This is however not the case, as a careful examination of the transport equations shows that in graphene transport relation time τtr diverges like 1/|ε - εF| for ε → εF, resulting in a finite non-vanishing σxx(ε) at ε = εF. For the relevant details, consult the contribution by Koshino and Ando to [1] (Sec. 6.4, p. 184). For a short overview of the physical properties of graphene, consult [2].

[1] H Aoki, and MS Dresselhaus, editors, Physics of Graphene (Springer, Heidelberg, 2014).

[2] MI Katsnelson, Graphene: carbon in two dimensions, Materials Today 10, 20 (2007).

Article Graphene: Carbon in Two Dimensions

Dear Behnam,

If density of states is zero as you are suggesting at Dirac point, then who carry current and contribute some finite conductivity?

Gokaran Shukla : I gave the relevant reference - referring also explicitly to transport equations, so you can obtain the answer to your question in there.

Hi Balkrishna

By opening gap (substrate effects, Coulomb interaction at two sublattices, ...), the graphene can be used as semiconductor.

Article Band gap opening in graphene: a short theoretical study

Balkrishna Choubey , semiconductor is characterized by its bandgap. I think that pure monolayer graphene cannot be assumed as semiconductor after all.