Eigenvalues of $\Delta u +u^p$

Question

Can you give me a book reference about eigenvalues of the operator $L(u):=\Delta u +u^p$ defined in the Sobolev Space $W^{1,2}(\Omega)$ with $\Omega\subseteq \mathbb{R} ^n$ a bounded domain and $p \in \mathbb{N}$?

Thanks in advance.