Basic semiconductors

[Jinnie]

In an n-type semiconductor, the n-type impurity( say P) makes bond with the neighboring Si atoms and gives off 1 electron. Though it loses 1 electron but still its octet is complete, so why P atom considered to be a +ve ion?

 

[albert22]

The n impurity has 5 electrons in the outermost shell. four are used to bond with the neighbor Si atoms. This results in one free electron for conduction. The n impurity is then called donor.
A p inpurity has 3 electrons in the outermost shell. This leaves one of the 4 bounds of the neighbor Si atom unoccupied. This unoccupied bound is free to move and it is called a hole. Electrons and holes free to move make possible the conduction of a current. The p impurity is called acceptor because it grabs an electron from a Si atom.
In both cases the impurities became ionized. The acceptor being a negative ion and the donor a positive ion.

 

[ashubrads]

In an n-type semiconductor, the n-type impurity( say P) makes bond with the neighboring Si atoms and gives off 1 electron. Though it loses 1 electron but still its octet is complete, so why P atom considered to be a +ve ion?

Basically what happens is that an n type impurity(say P) loses one electron and so it become deficient to neutral state by "1" and thus it becomes a positive +ve ion.. I hope it makes sense.. !!

And, Please let me know if I'm wrong.. !!

 

[Jinnie]

Thanks Albert & Ashubrads but I want to ask is why P atom becomes positive when its octet is complete( even after losing the electron). It should be neutral ,right?

 

[albert22]

The donnor has 5 electrons but only 4 are bonded to the Si atoms. With little energy (i.e from temperature) it becomes free leaving 4 out of 5 electrons for the impurity it is then a positive ion.
The acceptor only fills 3 bonds with the Si atoms. So there is a unoccupied bond on one of the Si atoms, which grabs an electron from somewhere else. Adding an extra electron to the 3 of the acceptor. The impurity becomes a negative ion with the 4 bounds occupied.
Hope that this helps.

 

[ashubrads]

A P atom is pentavalent in nature but it can have only 4 electrons bonded with silicon which is quadrivalent. So under the external influence like temperature,photon excitation etc (even if energy is very low) it loses it's single unbonded electron( 1 electron is left unbonded after forming bonds with silicon) and thus it becomes a positive ion.

i hope it must have given you complete answers and if you need further more info,then please post.

 

[adi0803199]

Even though P has its octec complete.in a covalent bond the two atoms are said to share 1 electron to form a single covalent bond.Now following this analogy ,if P atom bonds with 4 different C atom to complete its octec which makes it non reactive or inert gas configuration.The atomic number (P= 15 number of protons) is charge in the nucleus but the number of electrons that P effectively holds is (2,8,4) charge of outer shells is 14.So the net charge of the atom is (+15+(- 14) =+1).I hope this helps.