When bandgap increases or decreases on doping what physical phenomena occurs in system. What type of doping element it will increase and decrease. Any literature regarding the same.
I am simulating Eu doped WO3 using VASP. For pure WO3 using PBE functional bandgap is coming around 1.3 eV and with Eu doped it is coming 1.91 eV. So what is the reason behind increasing bandgap.
Shilendra
It all depends on where the fermi level of the dopant really is, which in turn gives rise to band tails. This leads to the effective decrease or increase in the band gap.
An over simplified example would be when the dopant material has a conduction band/valence band energy in between the cb and vb of the base material, it would create a band tail and effectively lower the band gap.
I hope it helps.
Thank You Aditya for your discussion and suggestions.
Shilendra
Dear colleague Dr. Shilendra Kumar Sharma
Have a nice time and good day.
Doping may affect the optical band gap to be high or low. what is the reason? firstly, the optical band gap increases or decreases according to the density of localized states; low or high respectively. XRD, SEM and TEM are useful techniques to produce the details of localized states. Ex. if the intensity if XRD increases and the FWHM decreases with the increasing doping ratio, this is a document that the increasing of doping gives more enhancement of order and the localized states or defects decreases by the increasing of doping which means the increasing of crystallite size otherwise vice versa. TEM can confirm the XRD data and SEM gives you what happen for the surface morphology. You can use SEM to check if the sample under consideration has a porous nature or not; porous nature is strongly affect the optical band gap. Please see the the attached file.
I wish that is useful and help you.
yours
A. El-Denglawey
Thank You Dear Dr. A. Eldenglawey for your help and discussion !
Shilendra
In Addition to above answers, you may consider the type of the semiconductor material under study whether it is p-type or n-type. If the material is p-type then after doping, band gap will decrease because of reduced number of majority carriers and vice versa. But.... cannot ignore the structure of the material.
Also, I would like thank Prof. A. Eldenglawey for such a nice information for readers. Great
Regards
Abdul Ghafar Wattoo
High doping densities cause the bandgap to shrink. This effect is explained by the fact that the wavefunctions of the electrons bound to the impurity atoms start to overlap as the density of the impurities increase. For instance at a doping density of 1018 cm-3, the average distance between two impurities is only 10 nm. This overlap forces the energies to form an energy band rather than a discreet level. This impurity band reduces the energy band of the host material by:
Eg = -22.5* (N/10^18)^1/2
The band-gap is a region in energy with no allowed states. The density of states versus energy depends on the chemical composition of the material; if the chemical composition is changed, at least, in principle, the state density distribution should change. Dopants are impurities, so, the chemical composition changes by doping. The change in the energy distribution of the allowed states cannot have a general rule such as: the band-gap will decrease after introduction of impurities. Generally, those impurities are called dopants, which create allowed shallow states in the band-gap. Shallow states have small ionisation energies; and, when the doping density is high, the dopant states generate a band. If this band is very close to the valence or conduction band edge, the band-gap will decrease.
Dr. Samares Kar (IIT K)
Dear Dr. Amir Zada,
As you gave example in above post O and N doping vice versa. I am not getting orbital energy. What do you mean here orbital energy ? Can you elaborate much more ?
Thank you for your help
Shilendra
Increasing or decreasing band gap I think it depend on application of your metal oxide semiconductor. For Example me, I am focusing on semiconductors with small/ narrow band gap .. I dope those with wide band gap to decrease their band gap
. Increase or decrease in band gap will depend which element in the semiconductor is replaced by which element ,and depend on size of dopant
The decreasing or increasing the bandgap energy with doping depends also on the lattice distortion. In case of pervoskite materials the doping somtimes leads to increase the octahederal distortion resulting in decreasing bandgap.
One possible reason can be the presence of the orbitals of the dopant atom in the VB or CB. This leads to hybridization with the existing orbitals and results in shifting of the energy levels. We found this phenomenon in Ag2O. When Zn was doped in Ag2O a widening of the band gap was observed. Studying the DOS plots from DFT calculations led us to the above conclusion. Hope this helps.
- Article Zn doping induced band gap widening of Ag2O nanoparticles
Sir, could you tell me the empirical relation between bandgap (Eg=Ec-Ev) and doping(ND,NA).
Dear@ Shilendra,
The substitutional doping with very low doping concentrations decrease the bandgap. Please for this well known phenomena follow the paper: Article A New and Simple Model for Plasma and Doping induced Band Ga...
However, if the concentration increases such that it forms a mixed material the band gap may increase. The concept of the resultant band gap by mixing two semiconductors with Eg1 and Eg2 is that the resultant band gap will have an intermediate value.
Best wishes
Please see the following link:
https://www.youtube.com/watch?v=bferh8TyA-Y
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