Geometric PGF

Instead of the Moment Generating Function (MGF), for non-negative integer-valued discrete random variables $X$, we can define the $\textit{Probability Generating Function}$ (PGF), which is given by $p(z) = \mathbb{E}[z^X]$ for $|z| \leq 1$. Find the PGF of $X \sim \text{Geom}(p)$. Evaluate this function for $z = \frac{1}{3}$ and $p = \frac{2}{3}$.