Recall that a function $f: \mathbb{R}^d \longrightarrow \mathbb{C}$ is positive definite, iff for all numbers $N$ and $x_1, \dots, x_N \in \mathbb{R}^d$, the matrix $(a_{ij})$ with entries $$a_{ij} = f(x_j - x_i)$$ is positive semi-definite.

My question is: Let $g \in L^2(\mathbb{R}^n)$. Is the function $$f(z, y) =\int_{\mathbb{R}^n} g(x - y) \overline{g(x-z)} d x$$ positive definite on $\mathbb{R}^{2n}$?