A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way and is periodically repeated in three dimensions on a lattice. The unit cell is given by its lattice parameters, the length of the cell edges and the angles between them. In 1848, Auguste Bravais demonstrated that there are in fact only fourteen possible point lattices and no more. In a cubic system, the lattice parameter is the side length of a cube and angles between the edges are 90. The cubic lattices are an important subset of these fourteen Bravais lattices since a large number of semiconductors are cubic. The three cubic lattices are the simple cubic lattice, the body-centered cubic lattice and the face-centered cubic lattice as shown in Fig.3.3. The positions of the atoms inside the unit cell are described by the set of atomic positions (x, y, z) measured from a lattice point.