# Conceptual understanding of semiconductors - definition of holes

I am studying semiconductors and I have a very basic question on the definition of a hole. Why do we add up the contributions of holes and electrons when calculating the current density ( J = (n.q.un + p.q.up).E )? Aren't they equivalent? I mean, if the hole is the absence of an electron, what is the reason this equation holds? Wouldn't we be calculating a value of J that is above its real value?

Thank you

• because that's the amount the charges we can move? I don't see how the equation would add up if we didn't count the holes? – Marcus Müller May 16 '18 at 18:51

$$J = J_p + J_n = e(nu_n + pu_p)$$
$u_p$ and $u_n$ are respective mobilities.