Question

The width of forbidden gap in silicon crystal is $1.1eV$. When the crystal is converted into an n-type semiconductor, the distance of fermi level from conduction band is

• A. greater than $0.55eV$
• B. equal to $0.55eV$
• C. lesser than $0.55eV$
• D. equal to $1.1eV$

Answer 1

The correct option is C lesser than $0.55eV$

Let,
$E_f$ = Fermi energy level for silicon,
$E_i$= Fermi energy level for intrinsic semiconductor,
$E_g$ = energy band gap for silicon,
$E_c$ = energy of conduction band.
Now, for n-type semiconductors, $E_f>E_i$
Hence,
$E_c-E_f=\frac{E_g}{2}-(E_f-E_i)$

$E_c-E_f=\frac{1.1}{2}-(E_f-E_i)$

$E_c-E_f=0.55-(E_f-E_i)$

Therefore, the distance of Fermi level from conduction band is lesser than $0.55eV$.