First-Principles Approach to Mn-Doped Group IV Semiconductors: Comparison with Experiments and Outlook

We present an extensive theoretical and experimental study of the Mn-Ge dilute magnetic semiconductor, a material which - due to its high integrability with mainstream Si technology - may hold good promises for spintronic applications. Ab-initio calculations on several different systems containing isolated Mn impurities as well as small clusters (up to three Mn impurities) show that Mn has a tendency to segregate into the Ge matrix and to stabilize occupation of interstitial sites if these are coordinated with other Mn occupying substitutional sites nearby. Several different experimental characterizations (HRTEM, XRD, UPS, MOKE) performed on Mn ion-implanted systems are analyzed and discussed: a close comparison betweeen experimental evidences and density functional calculations allows a full understanding of the sample properties and to disentagle the contributions coming from the diluted and segregated phases. The complexity of this system shows that much has to be done still to understand the physics of these materials and to undisclose all their possible applications.