# I Work function and Fermi level

1. Mar 18, 2016

### M.A.M.Abed

why does work function measured from fermi level
while work function is defined by lowest energy required to remove an electron from surface of materials
and fermi level the level have 50% chance to occupation that's mean there is level above it have electron inside so why we don't measure from those levels

2. Mar 19, 2016

### drvrm

Since in metals electrons are filled up to the Fermi level, the minimum energy required to extract
an electron from a metal is assigned as its work function.

One 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 usually varies with the surface conditions of the same material.
For all practical purposes, work function can be taken as a bulk property
.
However if one looks up the same Work Function
for semiconductors, there are energy band gaps, and so electrons may not be coming out of the Fermi level.
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 one calculates the work function, the energy difference between the bottom of the conduction band and the Fermi level must be added .
That is why the work functions of p- and n-type of the same semiconductor (say, Si) are different.

3. Mar 19, 2016

### M.A.M.Abed

2nd in semi conductor dose you mean the work function will equal to electron affinity + between the bottom of the conduction band and the Fermi level ???
3rd the definition of Fermi level is only at 0 temperature other temperatures is 50% probability level for occupation does this mean work function definition WF=-e*vacuum potential-E(fermi) is theoretical definition at 0 Kelvin ??

4. Mar 19, 2016

### drvrm

basically i am a theory person in nuclear theory but i have seen some papers dealing with measurement of work function esp. in semiconductors as there is a large variation with theoretical models -i can give you some references shortly as i get some time ....

5. Mar 19, 2016

### drvrm

6. Mar 19, 2016