Improvement of Depth Resolution of VEPAS by Sputtering Techniques

Variable energy positron annihilation spectroscopy (VEPAS) allows to measure depthdependent defect profiles. While the depth resolution is still in the nm range for low positron energies, it broadens strongly at higher penetration energies. The reason is the broad positron implantation profile often described as Makhov profile [1].
To avoid this problem and to determine real defect profiles in a depth of several µm, one can remove the surface step-by-step or continuously by sputtering the surface away, e.g. by low energy Ar ions. Of course, the advantage of VEPAS to have a non-destructing testing tool is lost. However, one gains from relatively sharp depth profile down to several µm and improved defect sensitivity in larger depth.
In the talk details of the sputtering process will be discussed and several examples of photovoltaic CIGS layers and defects after ion implantation in Si will demonstrate the power of this type of defect profiling.