Some papers have reported that band gap of ZnS increases with addition of doping element Ni. But in my experiment Band gap is decreasing. I am confused about the findings. Any inputs please.
Dear R. k
First of all in order to understand what is going we have to know something simple about the band structures of general materials. Each one has valance band, band gab (in the middle) and Conduction band. The insulator material has wide band gab (dose not allow to electron to jump from valance to the conduction band, The conductors have very small band gab where the valence and conduction bands may overlap, but a semiconductor is a material with a small but non-zero band gap that behaves as an insulator at absolute zero but allows thermal excitation of electrons into its conduction band at temperatures that are below its melting point
When the materials doped with an impurity for P-type the energy level of acceptor lies with a small interval Ea above the top of the valence band.
N-type the energy level of donor Ed lies with a small interval underneath of the conduction band. So Free holes (from acceptor atoms) and free electron (from donor atoms) can conduct electricity.
Therefore interaction with the band structure of the general materials between the lattice phonons and the free electrons and holes will also affect the band gap to a smaller extent. The relationship between band gap energy and temperature can be understood if we have a look to Varshni empirical expression,
The band-gap energy of semiconductors tends to decrease with increasing temperature we can understand the relationship between band gap energy and temperature can be described by Varshni's empirical expression (1).
where Eg(0), α and β are material constants.
So please note that: In a regular semiconductor crystal, the band gap is fixed owing to continuous energy states. In aquantum dot crystal, the band gap is size dependent and can be altered to produce a range of energies between the valence band and conduction band.[3] It is also known as quantum confinement effect.
Band gaps also depend on pressure. Band gaps can be either direct or indirect, depending on the electronic band structure.
Therefore Band-gap engineering is the process of controlling or changing the band gap of a material by controlling the composition of certain semiconductor alloys, such as GaAlAs, InGaAs, and InAlAs. It is also possible to construct layered materials with alternating compositions by techniques likemolecular-beam epitaxy.
1. H. Unlu (1992). "A Thermodynamic Model for Determining Pressure and Temperature Effects on the Bandgap Energies and other Properties of some Semiconductors". Solid State Electronics 35 (9): 1343–1352. Bibcode:1992SSEle..35.1343U. doi:10.1016/0038-1101(92)90170-H.
2. Jump up^ Temperature dependence of the energy bandgap. Ece-www.colorado.edu. Retrieved on 2013-04-03.
3. Jump up^ “Evident Technologies”. Evidenttech.com. Retrieved on 2013-04-03.
hope this help
Good luck
The band gap should decrease if compound semiconductor is doped with metal.
Dear Rehman,
Thanks for information. Can you please discuss the reason. I hope you will spare some time for it.
How are you measuring the bandgap?
You must be doping heavily your materials for this to happen.
In the low doping regime, the bandgap of a semiconductor should not change. What you change is the electron concentration, the position of the Fermi level. If this is what you are trying to achieve, you should lower your dopant concentration.
I am using two probe method and UV absorption to find band gap
The doping conc. is 1% 3% and 5%.
In fact band gap in this case is decreasing.
I came across three papers who have reported increase in band gap. That is why I got confused. thanks for your valuable reply
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