Molecular Beam Epitaxy is a deposition technique that allows for crystals to be grown with extremely high purity. The process allows for subnanometre control over the structure of the crystal as it’s grown and positioning of dopants within the material, as well as film thickness. A series of molecular beams are directed onto a heated crystalline substrate. Upon collision with the substrate, the molecules in the beam bind, forming a new crystal layer. The entire growth occurs in an ultra high vacuum and there is no chemical mixing before the beams reach the substrate surface.