In general, heteroatom doping in semiconductor systems generate intermediary energetic levels localized into band-gap of the pure semiconductor. This localization can be near valence or conduction band, such behavior is dependent of the heteroatom doping. To modify the valence band, a good choice is a doping from atom with more electrons than the atom replaced.
Thanks for S. R. de Lazaro's help. But what decides the position of valence band maximum of semiconductor? Could you give me some explanation?
In case of doping at ppm level, no change in the energy of valence band maxima and conduction band minima shouldshould take place. However, when hetroatom concentration is large, a new compound or alloy will be formed which may change the position of valence band maxima which will depend on atomic potential in the lattice. Without knowing the impurity atom and host material, nothing can be predicted.
If you have worked in experimental level, electrochemical results, such as, voltammetric experiments are indicate to estimate valence and conduction bands energies. Any amount of impurity as well as low or high, modify the valence or/and conduction bands, sometimes at very low amounts is very difficult measuring the effect caused. This fact occurs because the electronic structure is always affected when a new atom or molecule is introduces into molecular system.
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