Full Energy band Diagram

 In the earlier blogs we have seen how fermi energy level shifts in case of intrinsic, extrinsic semiconductor as well as how it acts when we add doping impurity to it.

Now we will see how actually band bending takes place in case of metals, oxides and semiconductors.

• EI = Vacuum energy level

• Ec= Conduction band energy

• Efp = Fermi energy level of mos

• Ev = Valence band energy

•  Φm = Work function of metal

• Xs = Electron affinity

• Eg = band gap energy

In the full energy band diagram of MOS ,  the most important point to be noticed are:

1. Continuity

2. Stability

The vacuum energy level or EI should be continuous for the complete device.

The reason behind this can be explained in the figure below

If the band is not continuous and some electron is present just above the vacuum level of metal , it might travel into the oxides conduction band which will disrupt the charge present in oxide.

For stability it is must that the fermi energy level is constant throughout the device i.e. same the fermi band level is at same energy in metal , oxide and semiconductor.

Bands in metal

The conduction band energy and valence band energy of metal lie very close to each other. We can say both energy levels are same for metals.The fermi energy also coincides with the conduction band energy. 

Band gap of Oxide 

Oxide being an insulator , there is a large difference between the conduction band and the valence band. Metal oxides can have a band gap of 9 ev.

  In the oxides the band bend linearly because there is no depletion region . There exists a voltage drop because of energy levels of same bands in metal and semiconductor. Metal oxide bands link these differences so as to maintain continuity of band diagrams. 

Authors: Ruturaj Deshmukh,Dhanesh Manwani,Sukhanshu Dukare