Expert in: Kinetics of defect formation and annealing
- Materials science
- Defects and impurities in thin films: doping, implantation
- Atom, molecule, and ion scattering
- Deposition by sputtering
- Kinetics of defect formation and annealing
- Atomic, molecular, and ion beam impact and interactions with surfaces
- Heat capacity of amophous solids and glasses
- Nanoscale materials and structures: fabrication and characterization
Ion implantation is a technique for modifying the surface of materials by injecting precise quantities of atoms at the desired depth. It is widely used in doping semiconductors when manufacturing very large-scale integrated circuits (VLSI). Since it is a highly out-of-balance phenomenon (the incident atoms typically have energies millions of times higher than the atoms in the material), this implantation often generates new structures at the atomic level that can be exploited to improve the performance of high-tech materials, or may create problems to be overcome.
For instance, during the doping process, implantation creates defects in semiconductors by displacing crystal atoms, and this is damaging to integrated circuits. If there are not too many defects, the damage can be corrected by annealing and the dopant activated. If the density of the defects exceeds a certain threshold, however, permanent damage will appear in the materials and may make the devices unusable.
Inversely, ion implantation generates defects that can be used to modify materials. Implantation makes it possible to create defects near the surface that can later diffuse throughout the material and modify the composition of the lower layers by interdiffusion. In this way it is possible to change the emission wavelengths of quantum dots or wells and the properties of the magnetic layers.
Ion beams can also be used for highly sensitive quantitative measurement of the deep distribution of atoms in a material. In our laboratories we use various ion beam analysis techniques, in particular elastic recoil detection (ERD), a technique developed in our laboratories in the 1970s, and Rutherford backscattering spectrometry (RBS), RBS channelling and nuclear resonant reaction analysis (NRRA).