2009 27 c (1 Viewer)

[hjed]

Hi

Would anyone be able to explain that question for me (2009 27 c)? Success one and BOS sample answers say the electrons flows from n to p through the external circuit, but my text book and my understanding says electrons should flow from n to p through the junction (and hence p to n externally?)

Don't the electrons want to fill the holes?

Thanks

 

[HowToNoob101]

Yes the answers are correct. This is because: when the n-type and p-type are brought close together, the extra electrons in the n-type diffuses into the holes of the p-type, making the n-type slightly positive and p-type slightly negative. This allows an electric field to be created in between the two, known as the depletion zone. When light with frequency above the thresh hold frequence strikes this material, electrons are ejected (photoelectric effect), but because there exists the electric field the electrons are only allowed to flow in one direction. Hence, when light strikes the n-type, electrons are forced to travel through the external field, as the p-type is slightly negative (repels electron).

 

[hjed]

Thanks, that really helps!