Metalorganic vapour-phase epitaxy

Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. It is a process for growing crystalline layers to create complex semiconductor multilayer structures. In contrast to molecular-beam epitaxy (MBE), the growth of crystals is by chemical reaction and not physical deposition. This takes place not in vacuum, but from the gas phase at moderate pressures (10 to 760 Torr). As such, this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys, and it has become a major process in the manufacture of optoelectronics, such as Light-emitting diodes. It was invented in 1968 at North American Aviation (later Rockwell International) Science Center by Harold M. Manasevit. In MOCVD ultrapure precursor gases are injected into a reactor, usually with a non-reactive carrier gas. For a III-V semiconductor, a metalorganic could be used as the group III precursor and a hydride for the group V precursor. For example, indium phosphide can be grown with trimethylindium ((CH3)3In) and phosphine (PH3) precursors. As the precursors approach the semiconductor wafer, they undergo pyrolysis and the subspecies absorb onto the semiconductor wafer surface. Surface reaction of the precursor subspecies results in the incorporation of elements into a new epitaxial layer of the semiconductor crystal lattice. In the mass-transport-limited growth regime in which MOCVD reactors typically operate, growth is driven by supersaturation of chemical species in the vapor phase. MOCVD can grow films containing combinations of group III and group V, group II and group VI, group IV. Required pyrolysis temperature increases with increasing chemical bond strength of the precursor. The more carbon atoms are attached to the central metal atom, the weaker the bond. The diffusion of atoms on the substrate surface is affected by atomic steps on the surface.