What this unit is about?

[nhrock3]

"a silicon cristal is doped with 1000000000000000000 $$cm^{-3}$$ atoms of antimon"

how does $$cm^{-3}$$ represents a number of atom

why not just say
"a silicon cristal is doped with 1000000000000000000 atoms of antimon"

 

[MATLABdude]

That's a concentration. There are 1 x 10^18 atoms of antimony per cubic cm. You need doping level (concentration) in order to calculate semiconductor operation.

 

[nhrock3]

why cubic cm is cm with power of -3
and not power +3
?

cubic is power +3

 

[MATLABdude]

It is! If you know exponents, cm^-3 is the same thing as 1/cm^3. Something per cubic cm, as we say.

 

[nhrock3]

aaaaahhhhhhhhhhhhhhhh thanks