Electronic Devices Question 225
Question: The typical ionisation energy of a donor in silicon is
[IIT-JEE 1992]
Options:
A)
B)
C)
D)
Show Answer
Answer:
Correct Answer: C
Solution:
When donor impurity (+5 valence) added to a pure silicon (+4 valence), the +5 valence donor atom sits in the place of + 4 valence silicon atom.
So it has a net additional + 1 electronic charge.
The four valence electron form covalent bond and get fixed in the lattice.
The fifth electron (with net - 1 electronic charge) can be approximated to revolve around + 1 additional charge.
The situation is like the hydrogen atom for which energy is given by
For the case of hydrogen, the permittivity was taken as e0.
However, if the medium has a permittivity er, relative to e0, then
