@ DFT means density functional theory based on quantum mechanics.

Generally fermi level considered as zero energy in case of most materials. But always fermi level do not exit at zero energy.

Dear Md. Amran

The illustration clearly shows that following doping, the material turns metallic with a split-off band. The bands appear to be crossing.

Existence of states at Fermi level in DOS(or bands) alone does not mean that it is a metallic compound. Rather, absence of a forbidden region in the vicinity of the Fermi level means that it is a metallic compound.

In your case Fermi level has been shifted within the conduction band due to doping which makes this material a n-type degenerated semiconductor. (If the Fermi level had shifted within the valence band then it would make a p-type degenerated semiconductor).

https://en.wikipedia.org/wiki/Degenerate_semiconductor

Rushikesh Pokar

Thanks You for given your answer. The information is very important for me. I try to understand the information in more details.

Sohail Hamid Dar

But some published paper define it as semiconductor materials.

their band structure is similar to my calculated band structure.

But i confuse how is it semiconductor.

Md. Amran Sarker there are two types of semiconductors (1) intrinsic and (2) extrinsic. In intrinsic semiconductors usually Fermi level lies within the forbidden region exactly in the middle. In extrinsic (slightly doped) semiconductors this Fermi level shifts towards the valence band or the conduction band depending on the type of the doping (p-type or n-type respectively), still Fermi level is within the forbidden region. however upon higher doping concentrations the Fermi level shifts and lies within any one of the bands (which is observed in your case). this kind of material is called degenerated semiconductor.

It is still a semiconductor (since it has a forbidden region) but due to the position of the Fermi level it belongs to a different class of semiconductor.

I guess you have dopped the materials with electron-rich moiety, which behaves like an extrinsic semiconductor, as Rushikesh Pokar has already pointed out. Doping has shifted the CBM (Conduction Band Minima) to cross the fermi to act as a donor energy level. Probably this is a typical n-type semiconductor with the degenerate band in the fermi. It solely depends on the extent of doping whether it will behave as an n-type semiconductor or a metal.

Rushikesh Pokar Gaurav Jhaa

Thank you for kind your given information