Saved Bookmarks
| 1. |
What is an intrinsic semiconductor ? Deduce an expression for its electrical conductivity. |
|
Answer» Solution :INTRINSIC semiconductor is a pure semiconductor . Outer shell of such semiconductors are complete at `0K` and they behave as insulators. At room temperature, due to thermal agitation, a few ELECTRONS are freed creating small HOLES. Thus at room temperature a pure semiconductor will have equal number of free electrons and holes. Electrical conductivity `(sigma)` Consider a block of a semiconductor of length `l` in which the holes and electrons are moving due to ELECTRIC field.  If `n_(e)`, `n_(h)` represent electrons and holes density respectively and `v_(e)`, `v_(h)` their drift velocities, then `I_(e)=en_(e)Av_(e)` and `I_(h)=en_(h)Av_(h)` or total CURRENT, `I=I_(e)+I_(h)=e(n_(e)v_(e)+n_(h)v_(h))A`............`(i)` We know `R=(V)/(I)` and `R=rho(l)/(A)` or `rho(l)/(A)=(V)/(I)` or `rho=(VA)/(Il)=(EA)/(I)` Since `V//l=` Electric intensity `E` Conductivity of semiconductor , `sigma=(1)/(("Resistivity" rho))` or `sigma=(I)/(EA)=(e(n_(e)v_(e)+n_(h)v_(h))A)/(EA)` or `sigma=(e(n_(e)v_(e)+n_(h)v_(h)))/(E)` `=e[n_(e)((v_(e))/(E))+n_(h)((v_(h))/(E))]` `sigma=e[n_(e)mu_(e)+n_(h)+mu_(h)]` where `mu_(e)(=v_(e)//E)` and `mu_(h)(=v_(h)//E)` are called electron and hole mobility respectively. |
|