Why transistor is so difficult to understand?
intuition of the operation of a bjt is more difficult than the intuition of a mosfet but the equations of the model of a bjt are much simpler than those of the model of a mosfet. nature gives and takes away.
it is not difficult to understand at all. I can not speak for the PhD in some universities, but anyone with an undergraduate degree in ee, and probably a bachelor’s degree in physics, should know how the transistors work indoors and outdoors. Of course, if you are applying for a PhD in literature, your answer may not be clear.
If you are obsessed with power, you may be confused by pnp and npn transistors. for both types, the base transmitter junction must be forward biased to get transistor action. when the junction is forward biased, the transmitter sends its carriers into the base. the base also sends its bearers into the transmitter. if the number of base-to-emitter carriers equals the number of carriers from base-to-base, the action of the transistor will not occur much.
The transistors are constructed such that the number of base-based emitters is much larger than the base-to-emitter number. sometimes up to 100 against 1. the base is very thin, so that the movement of carriers injected into the base by the transmitter continues and ends up in the collector. In short, if the ratio is 100: 1, for each load placed in the base, you will have 100 loads in the collector.
it is difficult to understand exactly what happens when we do not understand the physics of semiconductor devices.
In general, we take for granted that the current flows from the transmitter to the collector. while moving, some of the carriers recombine in the base and others move to the collector region. If more carriers recombine in the base, there will be less carrier flow in the collector region (less current in the collector).
In order to thwart the recombine carriers in the base (after a while, all the carriers in the base escapement and other carriers will no longer be available for recombination), we provide additional carriers in the base. This is what we call the basic stream. where we apply our required signal and operate the transistor in a linear (active) region to obtain amplification.
again, it is necessary to understand the transistor’s doping profile, the inverse / direct polarized working profile (how the energy bands move), the interaction between the p-type and n-type semiconductors. they are assembled, etc. to master the transistor. transistor and I think it’s worth studying about it as an engineer in analog .