Prac: Modelling Semiconductors (1 Viewer)

[Constip8edSkunk]

I just realised this point today.. how would you model the behaviur of a semiconductor with reference to conduction via holes and electrons?

I'm not sure what they mean by "model"...

would just drawing the atomic lattice structure with -/+ 1 electron be good enough?

and what do u do for the conduction bit?

line up a few peanuts, leaving a gap in the middle, move 1 peanut at a time and watch the gap move in the opposite direction? lol.

 

[ND]

I was looking at this dotpoint right now too, and am looking for info on it (i'm looking through various summaries for a good demonstratrion). CSU has something using egg cartons and ball bearings, but i don't understand it...

 

[Takuya]

Oh shit... not this practical. It's some crappy egg carton thing or with checker boards.

It's so stupid I don't think I did it. Did anyone here do this practical? How did you do it?

 

[Skywalker]

Originally posted by Constip8edSkunk
line up a few peanuts, leaving a gap in the middle, move 1 peanut at a time and watch the gap move in the opposite direction? lol.

lol that's basically what we did in class. Cut out a big rectangle, drew squares on it and put a cross into each square. Then we cut up small individual squares, put a minus on it and ta-da...your peanut experiment (albeit a little bit more professional looking).

 

[Constip8edSkunk]

lol this is a stupid dot point ...but yeah

from CSU
A procedure to model the behaviour of semiconductors
Place two separated halves of an egg carton side-by-side and 5 cm apart.

Place a ball bearing into each of the egg holders in one side of the egg carton. The ball bearing represents an electron. This side will be the VALENCE BAND.

Now remove ONE ball bearing from an egg holder in each row. This represents doping a semiconductor to create a hole.

Raise ONE end of the half of the egg carton containing the ball bearings until a ball bearing falls into the space left by removing the first ball. Raising the carton represents the applied potential difference. The movement of the ball bearing represents the electron movement and the apparent movement of the empty egg holder represents hole movement.

Repeat the first two steps EXCEPT place extra ball bearings (electrons) between the egg holders. This represents doping a semiconductor to create an n-type.

Slowly tilt the half of the egg carton containing ball bearings TOWARDS the empty half.

Stop tilting when ANY of the extra ball bearings make it across.

hmmm...so we are supposed to model the band structure of semi conductors and how ptype and ntype conducts

i see what the procedure is trying to do.... but why bother tilting, lol why not just do it manually.

 

[ND]

"Place two separated halves of an egg carton side-by-side and 5 cm apart."

Does that mean you take an egg carton, and cut it longitudinally so that you've got two separate pieces of one row, or do you have 2 two-row containers?

 

[Takuya]

This is hilarious...

 

[Constip8edSkunk]

i dont think it matters that much.... but 2 single rows would be better.. i think. i hope they dont ask a question on this point, because its kind of ridiculous lol

 

[ND]

Ok, but what is the purpose of having two of them? And why do they place extra ball bearings *between* the two egg holders?

 

[Constip8edSkunk]

the band theory of the n-type semi conductors say that the extra electrons occupy a donor layer just below the conduction band and can readily jump up to conduct electricity, i think thats what its trying to show, albeit dodgily hehe

 

[ND]

Hmm i must have it pictured completely wrong:

________
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OOOOOO
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Ok that's how i have them pictured, two egg carton things (single rows), how is placing ball bearings in between them gonna demonstrate anything? (I wish they included a diagram)

 

[Constip8edSkunk]

hmmm i read over it again i see what you mean cuz they said 2 separated cartons in the beginning... i orignally imagined them being connected anf you have the extra ball bearings in the middle on top, so when u tilt it they drop into the empty carton.... as they said wait until any of the "extra" ball bearings makes it across...hmmm

yeah i'll end up bullshitting whatever comes to my mind first

 

[Inhuman]

we did this experiment
we used ping pong balls instead of ball bearings. To get the n-type you fill all six holes of your egg carton and then balance another few on top. Then you manually put some into the holes in the other egg carton and that's your potential difference across the p-n junction
Then you go and play handball with the ping pong balls