Gallium Arsenide

3D Model

Gallium arsenide is used in LEDs. It is a semiconductor. Like silicon it has the lattice of diamond. Every atom is evenly surrounded by 4 neighbours. It is connected to each of them by a pair of electrons. In GaAs arsen gives 5 electrons and gallium 3 to the 4 bonds. Bonding orbitals are not symetrical as Ga atoms are slightly bigger then arsenic atoms. It is so because the bigger charge of the nucleus the more compressed orbitals become. Stronger nuclei have more electrons yet it does not usually compensate for the compression.

The orbitals in the model are not a result of a calculation but only of reasonable thinking. Probably nobody knows the real shapes.

Looking at the models it is easy to say why diamond is an insulator. The 8 bonding electrons, quite close to the center of charge of the core, are strongly attracted by the core, thus difficult to free. Needed energy is 5.5 eV. In silicon the core has the same charge +4e, but they are much farther. You need only 1,1eV, and in GaAs 1,4eV.