1. Home
  2. Hobby Electronics Basics
  3. n-type sample of silicon

n-type sample of silicon

One question,

"An n-type sample of silicon has a uniform density Nd= 10(power 16) atomes cm(-3) of arsenic. Find out the temperature at which half the impurity atoms are ionized. Assume that all mobile electrons and holes come from dopant impurities".

don't understand the question at all. If assume all electrons come from dopant, that means I should I consider the intrinsic carrier? So, as temp goes up, some dopant get ionized, half which is 0.5 X 10(power 16) is the current. if intrinsic is not allowed to consider, can I still use p = Ni(power 2) / n to find p?

thanks, I guess I don't get the meaning of this question. Any comments is appreicated.

Reply to
PZ
Loading thread data ...

For materials in equilibrium, I think it holds.

My general understanding is that at room temperature nearly all of the extrinsic dopant electrons are thermally ionized into the intrinsic's conduction band and that almost none of the intrinsic's electrons are ionized. This is seen on a plot of electron density versus inverse- Kelvins.

But that isn't the question, really. The question is about at what temperature it would be the case that there would .5e16 be ionized.

Perhaps this will help:

formatting link

I'm thinking of figure 2.6.8 and the material both above and below it.

Jon

Reply to
Jonathan Kirwan

Me neither. The way semiconductors were explained to me, a millennium or so ago, all of the dopant atoms are "ionized" all of the time, no matter what - that's what makes it an N-type semiconductor. They have no choice but to "ionize", because the valence electron won't fit into the crystal lattice.

When a copper wire is carrying current, do the copper atoms get "ionized?"

But, I'm confident that someone who knows their elbow from a hole in the ground will help clear this up for both of us. :-)

Thanks! Rich

Reply to
Rich Grise

They can 'freeze out' if the temperature is low enough.

You might think about this in terms of positive and negative attraction forces versus thermal energy. The extrinsic materials, if the temperature were at absolute zero or close to it, would keep their electrons very near their nucleus by + and - attractions. The probability of such an electron being buffeted away would be extremely low and near 0K temperatures. But since that net attraction isn't very strong in the case of extrinsic materials embedded in a silicon lattice, it doesn't take a lot of thermal jostling to bump them "up" into the conduction band of the silicon. At room temperature, none of them are able to settle for any length of time with an extrinsic nucleus. They keep getting kicked back up. So it appears that "all" of them are in the conduction band. But if you lower the temperature, there is less and less thermal energy and the probabilities shift. But we are talking "very cold" to reach 50%, even -- approximately the boiling point of liquid nitrogen at 1 atmosphere pressure, I think.

Jon

Reply to
Jonathan Kirwan

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.