Unitary representations of $SL(2,Z_n)$ and $SL(3,Z_n)$

Question

I would like to ask "is there a classification of unitary irreducible representations of $SL(2,Z_n)$ and or $SL(2,Z)$?"

Also, is there a classification of unitary irreducible representations of $SL(3,Z_n)$?

Here $Z_n=Z/nZ$.