Reflection high energy electron diffraction (RHEED) is a powerful technique for studying the structures of crystalline materials. It is a tool that allows the monitoring of the growth process with accuracy, providing information about the epilayers thickness, growth rate, surface roughness, and even the configuration of the surface (reconstruction processes).
RHEED uses an electron gun to send high-energy electrons at a grazing incidence to the substrate. After undergoing diffraction, the electrons interfere constructively at specific angles according to the crystal structure and spacing of the atoms at the sample surface and the wavelength of the incident electrons. A fraction of these electrons collide with a phosphorescent detector, creating specific diffraction patterns according to the surface features of the sample. The surface configuration and kinetics can be inferred by analysis of the diffraction patterns.
RHEED associated with MBE has allowed incredible progress in surface science over the past decades. Nowadays, it is routinely used to calibrate the fluxes of the MBE cells. It allows the growth of increasingly complex heterostructures where the layer thickness must be of atomic precision.
Our system is equipped with a 15kV STAIB RHEED gun and kSA-400 detection system. In collaboration with kSA we implemented their Rotational Monitoring And Triggering (RMAT) system which give us the unique capability to simultaneously monitor surface reconstruction of up to 4 azimuths during real-time growth on rotating substrates.