Subject: Physical Chemistry · Chapter: Solid State Chemistry · Topic: Band Theory · Exam: CSIR-NET 2011 · Marks: 2 · Difficulty: Medium
Consider a n-type semiconductor whose $\mathrm{E}_{v}=0, \mathrm{E}_{C}=2.0\mathrm{eV}$ and $\mathrm{E}_{D}-1.98\mathrm{eV}$. The correct statement among the following is
(a)$E_{F}=1\mathrm{eV}$ and is independent of T
(b)$E_{F}=1.99\mathrm{eV}$ and remains independent of T
(c)$E_{F}=1.99 \mathrm{eV}$ and increases towards 2.0 eV with increase of T
(d)$E_{F}=1.99\,\mathrm{eV}$ and decreases with increase of T
Answer
Answer (as printed): D
Explanation
At T = 0 K, the Fermi level lies exactly halfway between the bottom of the conduction band and the donor level. But as temperature is increased, the Fermi level drops (i.e., $E_{F}$ decreases).