about the avalanche breakdown

[arsenal]

can anyone give me some detailed description of the avalanche breakdown?
and before the breakdown, how does the reverse bias volgate affect the leakage current? why?

thanks a lot

 

[Loq]

It is a question of avalanche multiplication process which provides an internal gain. An incoming photon produces an electron-hole pair that are accelerated in opposite direction by the electric field. These carriers may collide and ionize atoms, producing other electron-hbole pair. Below the breakdown voltage, the avalanche dies after a few nanoseconds. A space charge charge appears and reduces the effective electric field leading to avalanche extinction. Puse heigth depends on mean optical power received on diode. above the braekdown voltage, the electric field is sufficiently high to overcome the sapce charge effect. Triggered, the avalanche grows exponentially until being limited by the diode resistance (low valu si high current!).If not quenched the current flows through the diode until its detruction by heating.
Below breakdown, I think that the leakage current increases with the reverse voltage. See datasheets for more precise information on incraesing rate and absolute value.
I hope i'll lep you.

 

[arsenal]

It is a question of avalanche multiplication process which provides an internal gain. An incoming photon produces an electron-hole pair that are accelerated in opposite direction by the electric field. These carriers may collide and ionize atoms, producing other electron-hbole pair. Below the breakdown voltage, the avalanche dies after a few nanoseconds. A space charge charge appears and reduces the effective electric field leading to avalanche extinction. Puse heigth depends on mean optical power received on diode. above the braekdown voltage, the electric field is sufficiently high to overcome the sapce charge effect. Triggered, the avalanche grows exponentially until being limited by the diode resistance (low valu si high current!).If not quenched the current flows through the diode until its detruction by heating.
Below breakdown, I think that the leakage current increases with the reverse voltage. See datasheets for more precise information on incraesing rate and absolute value.
I hope i'll lep you.

thank you very much.
For examle, a pmos transistor, and the gate is 4v, the source is -6v, and the nwell is 0v, then there is a depletion region at the nwell-p+ junction, and because of the voltage applied at the gate, the depletion region will fold to the souce side at the interface of the overlap of the gate oxide and the p+, there will be a vertical electric filed Ev of vg-vs and a horizontal electric field Eh, and when the Vg goes higher, the Ev will go higher and the total electric field Et will go high and impact ionozation will occur. Then the leakage current will go up linearly as to the Vg.
Suppose Vg1>Vg2, then leakage current of Vg1 will be higher then that of Vg2 before the avalance breakdown, then why will the two still break down at the same voltage? that is , since Vg1 let the junction get Ecritical more earlier then why will it still breakdown at the same voltage as when vg2 is applied ?
and i am clear about the space charge effect you mentioned, can you give me more explanations?

thank you very much

 

[Loq]

Hi Arsenal,
Excuse me but i don't see where is the problem. The electric field depends on the voltage Vgs. The leakage current before breakdown too. The breakdown corresponds to a critical electric field that is fixed (included in the process variations) so braekdown will occur for the same voltage. Please let me know...

 

[arsenal]

hi Loq,

since impact ionization happens at Ecrit, it is the mechanism of the avalanche but the breakdown still doesnt happen yet, and from this point till the breakdown, the leakage current is not exponential to the bias voltage and in fact the relationship is linear!
then what i wanna know is why the current is still not exponential to the bias voltage while the ionization has already happened?

thank you very much, really regret not have put much attention when learning semiconductor physics