(1) You say that "energetic photon can induce electron-hole generation". Actually the first video on transistor says that at room temperature, in other words, heat/thermal energy can also do that. (2) The second video on p-n junction / diode does say that photons, ie light energy can also do that (induce electron-hole pairs. In other words, light/photon is not the only way, The other way is heat/thermal energy. Please let me know if you agree with me, or comment on my statement, before I suggest where to move on from here to answer your question.. Cheers.

You might also need to specify the condition of electron/hole pair generation, and currents, eg. at equilibrium (zero bias) state, or biased state. I would suggest to use the definitions and terms in the following Wikipedia column's Section on equilibrium state and Figure A. (3) p-n Junction - Wikipedia en.wikipedia.org/wiki/P%E2%80%93n_junction. Cheers.

The gap between valence and conduction bands in pure silicon is about 1.1eV. Between donor and conduction bands and acceptor and valence bands in P and N doped silicon is about 50meV, a factor of about 22. There IS a small amount of thermal generation (ionization) at room temp producing electron and hole carriers, but it's small (minority carriers). The addition of dopants vastly increase the concentration of charge carriers in both bands (majority carriers) and reduce the minority carriers. Thermal generation is not the primary source of charge carriers in either band in the PN junction.

Just a quick reply. I very much agree with you that the thermal generated electrons and holes are too little in quantity for us to to consider in our discussion. So let us focus on the electrons and holes (in much bigger quantity) created by the dopants. / to continue, ...

The addition of an N-type dopant increases the number of conduction band electrons without a corresponding increase in hole concentration in the valence band (and even decreases it with more electrons available to thermally neutralize those holes through recombination). Similarly, a P-type dopant increases the number of valence band holes without a corresponding increase in electron concentration in the conduction band (and even decreases it with more holes available to thermally neutralize those electrons through recombination).

But I was wrong in saying that a photon is the ONLY bridge between valence and conduction bands. I've removed that part from my question. So, thanks for your contribution. I'm learning, myself. I'm hoping an expert will come along who knows the physics well. An electron in the conduction band of the N-type could cross the junction and form a net negative region in the P-type's conduction band or it could fall down to the P-type's valence band and annihilate a hole and still create a net negative region. And vice-versa. Hence the confusion. But the vids say 'fill a hole', so...

Just another quick reply. No worries. We can learn together. I just downloaded a free eBook to refresh my memory. You might might to check it out to see if we can use it for our reference in discussion.

This 2nd ed is almost 20 years old. But I think it is still very useful if we just use the chapters in physics and forget the chapters on technology. I think the physics part don't change that much in 20 years.

Ah, lunch time. See you later. Cheers.

I am skimming the first couple of chapters, and copying some critical pages for future reference.

You might like to read my comments and answer to the following question. electronics.stackexchange.com/questions/512032/…. Cheers.