When Fermi energy crosses the conduction band, then what will be the material? n-type semiconductor or metallic?
Hi,
The short answer is yes. For a detailed explanation, I would like to redirect you to an old thread with a nice explanation. Hope it helps!
https://www.researchgate.net/post/Why_does_Fermi_level_shift_toward_conduction_or_valence_band_with_doping
Best,
Faizan.
Fahmida Parvin Are you talking about conduction band edge or conduction band. If your question is "Can Fermi energy cross the conduction band edge Ec" then the answer is yes and when the fermi energy level lies with in the conduction band then it is called Degenerate semiconductor.
One cannot define Fermi energy level above the conduction band because the definition of Fermi energy itself says "It is that energy level above which all the available energy states are empty and below which all the available energy states are filled at thermal equillibrium". Above the conduction band there is a vacuum level and no available energy states so fermi level does not exist. Hope it helps.
For further information, I have attached a book you can check it out.
To answer your specific question, "can the Fermi level be higher than the band", the answer is a big yes. Extreme doping is used in many semiconductor devices, and this can also happen by injecting current into the devices such as laser diode.
See also:
www.physics.stackexchange.com/questions/161102/can-the-fermi-level-go-above-the-conduction-band-energy-if-doped-heavily-enough
Sritrakool, W., H. R. Glyde, and V. Sa-Yakanit. "The Fermi energy and screening length in n-type GaAs." Canadian Journal of Physics 60, no. 3 (1982): 373-378.
Dear Fahmida Parvin,
1 part: Yes, the new fermi level(after doping) can move inside the conduction band when the doping of the n-type semiconductor is very very high.
2 part: It will still behave as a semiconductor( because we can still control the flow of charge carriers through biasing) but only upto some doping level. If we still increase the doping higher than that, then it will start showing metallic behaviour. Generally this doping level is 1:103 (after that semiconductor starts showing metallic behaviour).
3 part: It is applicable for any material but the doping level may vary for different semiconductor after which it shows metallic behaviour. So it will be still classified as n-type semiconductor upto that doping level.
A semiconductor material can be metallic in nature when Fermi energy crosses either conduction band or valence band.
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