question about PN junctions - Page 1
Forum section: electronics / beginners

author: vivi-d
author_rank: Regular Contributor
timestamp: April 23, 2022, 03:53:28 pm
content: Just wondering... if you had piece of N doped silicon (or P doped) would it be a conductor by itself?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 23, 2022, 05:39:36 pm
content: Silicon is a semi-conductor, which means that it conducts significantly less then "the average metal", but much more then insulators.https://en.wikipedia.org/wiki/SiliconDoping silicon is typically in the single digit ppm range or less, and this changes very little to it's overall conductivity.It is only the interaction between the N and P boundary layer that strange things happen.There is also a similar boundary layer between a metal and doped silicon, that is called a skottky diode.But the bulk material itself is just slightly resistive regardless of the small amount of doping.** Edit **Oops, I: )(*&^%$#@!As written below...A "clean" semi conductor, conducts a bit, and adding doping adds charge carriers, and thus indeed increases conductivity and decreases resistance.So I agree with the kind peaple below and I wrote down a bit of a brain fart here earlier.I'm sorry for that.

author: vivi-d
author_rank: Regular Contributor
timestamp: April 23, 2022, 05:57:31 pm
content: Thanks! That clears things up

author: magic
author_rank: Super Contributor
timestamp: April 23, 2022, 07:27:28 pm
content: Doping increases the amount of available charge carriers (free electrons or holes) and thus increases conductivity and decreases resistance.If you don't know whom to believe, see the chapter on resistorshere, for example.

author: MathWizard
author_rank: Super Contributor
timestamp: April 24, 2022, 07:29:43 am
content: Not long after they classified semi-conductors, they noticed they can be light sensitive too, so the material can conduct more or less, depending on the light level. The incoming photons can knock more electrons up in energy, into the conduction band, as they call it.https://www.youtube.com/watch?v=a3PXVakobDU&ab_channel=MrSmith%27sPhysicsonline

author: Kleinstein
author_rank: Super Contributor
timestamp: April 24, 2022, 08:13:30 am
content: The doping has quite some effect on the conductivity. The doping level is often given by the conductivity, not the actual concentrations.A somewhat tricky part is making the contracts. Because of surface oxide and contaminations at the surface one can not just put the DMM probles to the surface and expect a good contact. One may end up with a diode like contract.

author: vivi-d
author_rank: Regular Contributor
timestamp: April 25, 2022, 08:57:29 pm
content: I work on a bed of nails test systems, it seems contact is half of my job lol

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2022, 10:27:28 pm
content: A detail about charge carriers:If you look up the Hall Effect, it is interesting that the polarity of the voltage measured in the direction perpendicular to both the applied field and the current flow depends on the polarity of the charge carriers: positive holes or negative electrons.

author: hamster_nz
author_rank: Super Contributor
timestamp: April 25, 2022, 10:43:59 pm
content: Quote from: TimFox on April 25, 2022, 10:27:28 pmAre you coming here looking for trouble Tim, with all this talking of 'holes' carrying charge?

author: TimFox
author_rank: Super Contributor
timestamp: April 25, 2022, 11:36:00 pm
content: Back at university, I measured such things in an instructional lab.It's very revealing to see net mobility of these charge carriers as a function of temperature.