where can i read obut this formula..

[nhrock3]

i know that ni is the negative charge density in the intrinsic material
http://i44.tinypic.com/34ynqjl.jpg

but i dont know how to develop it?

[jasonRF]

Many books on semiconductor devices will likely have some sort of discussion leading up to this equation. One nice example is is the little paperback book
"Semiconductor Fundamentals", by Pierret. This is Volume I of a series on solid state devices and it is quite readable. The equation is a combination of equations 2.21, 2.13a and 2.13b from that book.

Deeper treatments can be found in books on solid state / semiconductor physics. For example, chapter 8 of Kittel's "Solid State Physics" covers this.

jason