Let's start straight away. In this book on page 4 Gallium arsenide's bond structure is shown like this:
$As$ is shown making $5$ covalent bonds.
Recently I came across this book. The bond structure of $GaAs$ is shown like this:
. Here $As$ is shown to make $4$ covalent bonds. For sure one of the above quoted images is wrong. But which?
Please explain in your answer the actual bond configuration of solid state $GaAs$, with established reference(s). Also give experimental proof in your answer that supports your answer.