- #1
mendes
- 40
- 0
how can we understand it please ? Thanks.
how can we understand it please ? Thanks.
Can you please provide some context and background for your question? What do you know so far?
http://www.google.com/search?source...02&q=metastable+deep+defect+in+semiconductors
.
When the deep level is excited, it changes the local electronic structure of the defect; bonds break and there is a shift in the local lattice structure (relaxation). That gives rise to a new shallow defect (for example). There is an energy barrier that prevents the return to the original deep level configuration. If the temperature is too low, the energy barrier is not overcome, so the new shallow defect is "stable". This is why photoconductivity persists even after the light is turned off. When the sample is warmed up, the barrier is overcome and the defect returns to its original deep level configuration, trapping the electron and persistent photoconductivity stops.
In my earlier post, I had linked to a paper that had a good explanation of the mechanism, but after consulting with mentors, I decided to remove it because it was a copyrighted paper. If you have access to the journal, this is the reference: D. J. Chadi, K. J. Chang, Phys. Rev. B, 39(14), 10063 (1989).
Do a search on DX centers or EL2 defects on Google. You can find lots of info on the mechanism.
The barrier is related to the structural shift that needs to occur to go from metastable to original configuration. If an electron drops into the metastable shallow state, it will not be trapped into the deep level unless the structural shift happens. Otherwise, it will just be re-excited thermally into the conduction band eventually.
The attached picture should explain a lot (including the second question).