what is the simplification of the following expression (in terms of gamma and\or other functions) ?

$\displaystyle \Gamma(xy)$

i tried the following :

$\displaystyle \Gamma(xy)=\int^{\infty}_{0} t^{xy-1} e^{-t} dt$

now let $\displaystyle t^x = s$

=> ( after some manipulation )

$\displaystyle \Gamma(xy)=\frac{1}{x}\int^{\infty}_{0} s^{y-1} exp{-s^\frac{1}{x}} ds$

but here is where i'm stuck .. so any help would be appreciated ..