Dopant stability and strain states in Co and Mn-doped Ge (001) epitaxial films

Systematic investigation of structural, chemical, and magnetic properties of Co and Mn-doped Ge (001) as a function of doping concentration reveals that codoping with Co can dramatically reduce phase separation and diffusion of Mn within the Ge lattice while it magnetically complements Mn. The measured strain states indicate the critical role played by substitutional Co with its strong tendency to dimerize with interstitial Mn. Selecting appropriate codopants that form energetically stable dimers in a semiconductor host is shown to be a viable approach, thus demonstrating the feasibility for engineering stable doped magnetic semiconductors.