A question about the working of BJT

[Magnethicc]

Hi everyone, I was wondering if you could answer a question I have:
In the case of a NPN Transistor in the active/saturation region - what is the primary reason for the collector to emitter current?
is it diffusion or is it drift?

 

[tepalia02]

diffusion

As far as I understand, it's diffusion current. Because this current occurs due to the diffusion of holes and electrons.

 

[danadakk]

https://www.ittc.ku.edu/~jstiles/312/handouts/section%205_1%20BJT%20Device%20Structure%20and%20Physical%20Operation%20package.pdf

View attachment 178358

Regards, Dana.

 

[timof]

In active operation of NPN bipolar transistor, electrons move form the emitter to collector, and the transport mechanism changes, depending on where they are:

- in the quasi neutral region of emitter (n-type), electrons are majority carriers, and move by drift (in a very weak electric field)

- from emitter to the base, the transport process is thermionic injection

- in the p-base, electrons are minority carriers, and move by diffusion, or, in the case of a built-in electric field (from dopant gradient, or from SiGe Ge dose grading) - by drift. If base is very thin, electrons can move ballistically or quasi ballistically.

- in the depletion region of base-collector junction, electric field is large, so electrons move by drift, with saturation velocity

- in quasi neutral collector, the transport is again a drift of majority carriers in a weak electric field.