of North Carolina - Chapel Hill
control both electronic and magnetic properties of semiconductors by doping them with magnetic dopants. The challenge is how to stabilize relatively high doping levels required for achieving high temperature ferromagnetism without destroying the semiconductor. Doping with a single element beyond several percent not only induces epitaxial strain, but also promotes phase separation and metallic behavior, thus making epitaxial growth unstable. In this talk we describe the MBE synthesis and characterization of promising new Ge-based magnetic semiconductors and heterostructures. We highlight key findings in the epitaxial phase diagram, and the novel magnetic and transport phenomena. We show that the use of two dopants with appropriate relative concentrations a range of desirable 'compensation' effects can be achieved, including compensation of strain and carrier effects caused by the individual dopants, thus stabilizing epitaxial growth and semiconductivity at higher doping levels. Applying this approach to other multi-dopant systems opens new avenues for tailoring highly doped electronic materials.