Embedded Clusters In TM-doped AIAs: A First-principles Study

The transition-metal(TM) doped III-V type dilute magnetic semiconductors (DMSs) have recently been a major focus of magnetic semiconductor research because of their potential as spintronic devices. To perform density functional theory (DFT) calculations, the linear combination of atomic orbitals (LCAO) with SIESTA code has been employed. Our focus of the current work is the spatial distribution of Cr atoms in zinc-blende Cr:AlAs.Our calculations include single-doping, double-doping and multi-doping configurations with ferromagnetic and antiferromagnetic phases. Investigations into formation energy as a function of the distance between two Cr atoms are also implemented.Our systematic studies clearly show that the Cr ions prefer to occupy the substitutional Al sites in single-doping configurations. The most energetically favorable double-doping configuration is AFM CrAl-Cri-T1. For double-doping configurations, the Cr atoms have a strong tendency to form clusters with different magnetic ground state, such as AFM CrAl-Cri-T1, AFM CrAl-Cri-T2, FM CrAl-CrAl, etc. These results are different from substitutional CrGa(Al) clusters in wurtzite DMSs. Compared with homogeneous model, the coexistence of various AFM Cr-Cr clusters leads to reduction of the magnetic moments of Cr:AlAs. Also, due to the relatively small differences in the formation energies of different Cr clusters, the measured magnetic moments may be dependent sensitively on the growth temperature and the Cr concentrations. The above conclusions have been proved by the result of the multi-doping configurations.