https://www.researchgate.net/post/What_is_the_difference_between_work_function_ionization_potential_and_electron_affinity_in_a_semiconductor_What_do_they_physically_mean
Popular Answers (2)
Kanad Mallik added an answer
Hello Soumendu,
Good that you are asking after reading proper books. Unfortunately, many do the other way.
The
concept of work function is not limited to semiconductors. It is rather
more important for metals and was introduced in the context of metals.
It is an experimentally obtained parameter and is most simply determined
from the photoelectric effect experiment. Since in metals electrons are
filled up to the Fermi level, and there is no band gap, the minimum
energy required to extract an electron from a metal is assigned as its
work function. The question about bulk and surface is tricky. You
cannot extract electrons from the bulk of a material without extracting
it from its surface. So, strictly speaking, work function is a surface
property - it has been reported to vary with the surface conditions of
the same material. For all practical purposes, work function can be
taken as a bulk property if you know what you are doing.
If
you extend the concept of work function to semiconductors, there are
complications as they have energy band gaps, and when you are extracting
electrons by the same photoelectric experiment, electrons are not
coming out of the Fermi level. At any finite temperature, there are some
electrons available at the bottom of the conduction band, so the
photoelectric effect experiment gives a different quantity assigned as
the electron affinity of the semiconductor. Now if you still like to
calculate the work function, you have to add the energy difference
between the bottom of the conduction band and the Fermi level to the
electron affinity. That is why the work functions of p- and n-type of
the same semiconductor (say, Si) are different. This is also the reason
that the work function is not that much useful as a parameter for
semiconductors as the electron affinity.
The
dilemma of matching the definition of electron affinity in chemistry
and semiconductor physics is genuine. In the context of what I said
above, you may notice that physically they mean the same thing with the
energy measured in the opposite ways.
Hope this clarifies your doubts.
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