Ion Beam Tool Research Articles

Rare-Earth Doping by Ion Implantation and Related Techniques

ABSTRACTSome metal plasma techniques have been developed that provide a convenient means for the doping of semiconductor hosts with rare-earths. These plasma and ion beam tools are based on the application of vacuum arc discharges for the formation of dense rare-earth plasmas which then can be used in a number of ways for doping and otherwise introducing the rare-earths into substrate materials. At the low energy end of the spectrum, the streaming metal plasma can be used for the deposition of thin films, and if more than one plasma source is used then of multilayer structures also. Or by building the vacuum-arc rare-earth plasma generator into an ion source configuration, high current ion beams can be produced for doing high energy ion implantation; alternatively the substrate can be immersed in the streaming rare-earth plasma and by using appropriately phased high voltage substrate pulsing and pulsed plasma generation, plasma immersion ion implantation can be done. Between these two limiting techniques – low energy plasma deposition and high energy ion implantation – a spectrum of hybrid methods can be utilized for rare earth doping. We've made a number of plasma and ion sources of this kind, and we've doped a wide range of substrates with a wide range of rare-earths. For example we've implanted species including Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er and Yb into host materials including Si, GaAs, InP and more. The implantation dose can range from a low of about 1013 cm−2 up to as high as about 1017 cm−2, and the ion energy can be varied from a few tens of eV up to about 200 keV. Here we review these vacuum-arc-based plasma methods for rare-earth doping, describing both the tools and techniques that are available and the applications to which we've put the methods in our laboratory.