References: 1. https://doi.org/10.1016/S0022-0248(97)00108-5 (1997)
2. Journal of Solid State Chemistry 165, 35-41, doi:https://doi.org/10.1006/jssc.2001.9486 (2002)
These are important reference papers on this topic, but I fail to grasp exactly how the p-type doping occurs.
Will be grateful to receive help.
Dear Abhirami,
if Bi occupies a Se-site, you have an anti-site-defect. Bi is a member of the 5th main group, Se a member of the 6th maingroup. That means, Bi has in the outer shell one electron less than Se. Therefore one electron is missed if Bi changes to a Se site. This missing electron is a hole - so it could be that a p-type solid forms.
With Regard
R. Mitdank
From the point of view of solid state chemistry, the answer is obvious. In simple variant it is given by Dr. Rüdiger Mitdank. But in fact, the main questions is: What is the relative charge of BiSe (I doubt against reasoning about the number of valence electrons)? Why do such defects form in this "stoichiometric" compound? Do antisite defects really exist in this "stoichiometric" composition? Because then there should be Bi vacancies on "native" positions (also charged; by the way, what are your thoughts on where selenium goes?). Maybe there are deviations in the ratio of elements associated with the synthesis? What type of conductivity will be in substances with Bi/Se ratio less than 1.5 ? Is there a ratio with a minimum conductivity? What are the concentration limits of this phase? And so on...
Dear Vadim,
Yes, correct. In stoichiometric Bi2Se3 Bise formation energy is very high. As Se concentration decreases in the system, Bise formation energy decreases, In fact, according to Xue et al. (DOI: 10.1063/1.4804439), this particular defect is amphoteric. It acts as a donor in stoichiometric Bi2Se3 and acts as an acceptor below a particular value of Se deficiency/Bi richness. And about Bi vacancy also forming during formation of Bise, I had the same doubt. Bi vacancy introduces 3 positive charges in the system and Bise introduces 1 positive charge. So if a Bi atom leaves its lattice site to go and occupy a vacant Se site, then is this process introducing 4 positive charges?
Also, is the net formation energy for this process the sum of formation energies of Bi vacancy and Bise?
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