Molecular Beam Epitaxy

Molecular beam epitaxy (MBE) is a technique developed in the 1960s in the Bell laboratories and is widely used in semi-conductor research to grow very high quality, single crystal multilayers of III-V semiconductors. Our MBE system is dedicated to the growth of metal and more recently, oxide thin films and heterostructures.

The basic principle of MBE growth is the direct sublimation of solid source materials into a gas phase at very low pressures (typically we use 10-10 mbar) – because the gas pressure is so low, the individual molecules and atoms are able to travel many centimetres before they collide with another molecule. This means that everything inside the MBE chamber gets coated with a very even and very thin layer of the material being deposited. Because the deposition rate is very low, the atoms that land on the substrate have plenty of time to move around and settle into a single crystal structure before they get buried under the next layer.

Our MBE system can grow 6 different materials in one deposition cycle – three relatively low melting point metals can be grown from the Knudsen effusion cells, and for higher melting point materials there are three electron beam hearths. During growth, the film structure can be monitored by in-situ RHEED. A feature of our MBE system is that the substrate manipulator – which can heat substrates to over 1200°C – is equipped with a series of masks that can slide in front of the substrate to pattern the growing films.