- #1

paulzhen

- 33

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**Why n*p always equal to ni square?? (semiconductor)**

Hi,

For you guys who studied semiconductor physics must be familiar with the equation:

np=n

_{i}

^{2}

I can understand why this is true for the intrinsic case (the broken bonds would always provide electron and hole in pairs )

But why is this still true for dopped semiconductors? Take Si for example, n=p=n

_{i}=10

^{10}in intrinsic case (that's we all know). However, if dope 10

^{15}N

_{d}into the material, then n~10

^{15}and p~10

^{5}. The highlighted part is my confusion! Why p become smaller? Where do the holes go?

Thanks for helping!