Wurtzite crystal structure is a hexagonal pattern found in some semiconductors. This differs from the cubic crystal structure of diamond and zinc-blende latttices.
While in the cubic semiconductor structures, the distance between points of the Bravais lattice are the same in three directions, which are separated each by 90 degrees. In the hexagonal structure, only the distance between two of the three points are the same. The two points that are the same distance from each other are separated by 90 degrees, while the third point is separated by 120 degrees.
Materials with a wurtzite crystal structure include GaN, AlN, InN, and ZnO.
Both Silicon and GaAs are cubic semiconductors. Silicon is a diamond crystal, while GaAs is a zinc-blende crystal. Diamond differs from zinc-blende lattice in the composition of the atoms in the lattice.
Since Si is a pure substance, only Si atoms are present in the crystal lattice. A diamond crystal has 8 atoms, which include the corner atoms, atoms on faces, and internal atoms.
In the GaAs semiconductor compound, the corner and face atoms will be of a different atom than the internal atoms. For instance, the corner and face atoms can be the metal Gallium while the internal atoms are Arsenic.