# What this unit is about?

## Main Question or Discussion Point

"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"

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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.

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

cubic is power +3

MATLABdude