recombination concept - recombination life time, carriers

[nandinichakrab]

recombination concept

plz explain the concept of recombination. what is recombination life time? r minority and majority carriers separetely considered in recombination? plz explain fully.

 

[akshay_d_2006]

Re: recombination concept

I presume that you are talking in terms of the recombination taking place in the transistor.

A more broader viewing of the further answer will get more generic in terms of recombination.

Ions in a metal cant move due to covalent bonds.
electrons in valance band are of prime importance in understanding because they are the ones who are least attracted to the nucleus (and far away from them). Now when they get even a small energy ( in any form) then they disociate themselfs from the nucleus and ( High energy, rather highest and ∞ distance from nucleus) thus they are termed as free electrons. Now thay are formed by breaking the covalent bond with the help if that energy.(It is nothing but band gap energy)

Whenever a free electron is formed there forms, but obviously, a deficiency of electron where it was previously bonded. This is called as Hole. Thus hole is nothin but a deficiency of electron and it has the ability to attract electrons because there is relatively +ve charge(Hypothetical) as compared to the real -ve charge present on electrons. doping is a different therory
So when electron (free) forms an hole is bound to form.

This energy is given normally in terms of thermal energy. Thus the breaking of covalent bonds to form a electron-hole pair is called as thermal agitation.

Now when another free electron comes near the hole and in case it doesnt has enough energy to surpass it,meaning it has less energy and hence gets attracted to the nucleus, forming a covalent bond. This IS RECOMBINATION.

Mean Life time:
The no of electrons and protons generated due to thermal agitation are same. Thus it is must that the generated electron do recombine with a hole (i.e Broken covalent bond is again made). It means if a free electron gets its life(i.e BORN) then it is true that its life will end(RECOMBINATION).

This birth and death of electron is the case with many such electrons.
In their lifetime they suffer collision, b4 recombination.
The average of all times (t1, t2, t3.. -Times betn 2 sucessive collisions) for which diff electrons remain free is known as mean life time[/b]