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?
To how many $Ga$ atoms one $As$ atom is connected? Actually. Please explain your answer with established reference(s) and also give experimental proof in your answer that supports your answer.