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Semiconductors all have a reasonably sized band gap which enables them to conduct or not conduct current depending on applied voltages. A p-type semiconductor (as opposed to an n-type semiconductor) is one in which doping or the natural flaws in the crystalline structure promote hole generation. (Holes are effectively a missing electron in the sea of electrons, treated as a positively charged particle with negative mass).

Because these holes exist, they are the major contributers to current. This becomes important when creating advanced devices such as p-n junctions, where one p-type semiconductor is joined with an n-type semiconductor.

The holes are generated because some flaw or dopant creates a single allowed energy state in the normally forbidden band gap (a perfect semiconductor lattice could be neither n nor p type).

|    Conduction Band   
| -----------------------
|       Band Gap    energy state
|                    /  caused by dopant
|    - O - - - - - - -    (full of holes)   
| -----------------------
| O   O O O O O O O O O O 
|   | Valence Band \
|    \              \
|   hole           electron
+------------------> x direction
This graph shows holes as a blank space and electrons as a O. Note how the holes in the energy state caused by the dopant can travel down into the valence band where they contribute to current.

I'm not sure if my graph is too confusing. /msg me and let me know. Also if there is any additional information you would like to see, I am more than happy to add it.

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