2) Rare earth nitrides

In the field of spintronics, several types of architectures have been proposed: ferromagnetic metal / semiconductor, dilute magnetic semiconductors, or magnetic semiconductors. The activity developed at CRHEA aims to manufacture and characterize heterostructures based on rare earth nitrides (NTRs). NTRs have the particularity, at low temperature, of being both a semiconductor and magnetic compound. In the laboratory, the elaboration of the NTRs is obtained using a molecular beam epitaxy (MBE) frame, Riber 32p. NTRs crystallize in the cubic structure of sodium chloride (NaCl) and are therefore binary compounds between a member of the lanthanide column and a nitrogen atom. The materials developed at CRHEA are samarium nitride (SmN) and gadolinium nitride (GdN), which have remarkable electrical and magnetic properties. The evaporation of the rare earths Gd and Sm is carried out using an effusion cell. The atomic nitrogen can come either from a precursor gas, ammonia (NH3), but can also be obtained by catalytic effect between molecular nitrogen and lanthanides (in this case Gd and Sm). The scanning electron microscope image (Fig. 2 (a)) shows an example of an epitaxial layer developed by EJM on an AlN trench layer on silicon (111). The NTR thicknesses are of the order of 100-200 nm, whereas the GaN encapsulation layer makes it possible to passivate the NTRs, since they have the disadvantage of being very reactive in contact with the air. . As illustrated by the diffractograms of Figure 2 (b), the materials thus obtained are monocrystalline, which illustrates the interest of the EJM for the development of this sector.