N-type semiconductor generation

[sam_s.pitt]

I have got two questions about extrinsic semiconductors, say n-type Silicon.
1. Why just elements of the group 5 are used to generate this kind of semiconductors? Why do not use elements of group 6 to have two free electrons per doped atom?
2. Why doped atoms generate a valid energy level (donor level) very close to conduction band of Si? Why donor level is not next to valence band of Si?

 

[jeffrey samuel]

Hit some books before trying to post here both your qurstions are very well answered off in books

1st the 5th group atoms

they are the only group of elements in the periodic table to form four single bonds with Si and also have one electron in the valence level

next the 6th group elements eg Oxygen the don't have the capacity to form a single bond with Si and they tend to form more stable double bond structures with them

Donor electrons are free and they don't have any limiting covalent bond involving them second the molecular size becomes larger pulling the donor electrons away from the nucleus and thus they have lesser energy and this energy is much nearer to the conduction band energy of the Si molecule

Not all donors provide energy levels closer to the conduction levels only the 5th group donor atoms provide that all the 3rd group acceptors provide energy levels closer to the Valence band of the Si molecule

hope this helps

 

[dick_freebird]

The ionization potential of the second electron of a Group VI
donor is likely to be well outside the region between silicon
conduction and valence band. You want the dopants to be
active between, not outside, the bands.