Mn doped II-IV-V₂ chalcopyrites are promising candidates for room temperature ferromagnetic semiconductors. Although several materials such as CdGeP₂:Mn, ZnGeP₂:Mn have already been reported as room temperature ferromagnetic semiconductors, most of them are bulk materials synthesized at high temperature.

Among this category, we chose MgGeAs₂:Mn as a new candidate for MBE growth on GaAs substrates. Before the study of Mn doping, we investigated the growth of MgGeAs₂ on GaAs (001) and (111)B. Stoichiometric growth conditions were established with assistance of XPS measurements. On GaAs (001), RHEED, XRD and TEM revealed phase separation with the formation of Mg₃As₂ and surface roughening. On GaAs (111)B, we obtained single crystalline films of 35nm with a smooth surface and a lattice constant of 5.66Å at an optimized growth temperature of 600^oC and a BEP flux ratio Mg:Ge:As = 1:3.1:800. With flux variations of ±10%, Hall measurements at room temperature showed n-type conduction (n = 2e18~3e18) in Ge rich samples and p-type conduction (p = 4e17~2e19) in Mg rich samples.

Two ways of Mn incorporation were tried on (111)B grown MgGeAs₂: (1) in-situ solid state reaction by annealing a Mn layer deposited on top of MgGeAs₂ film at 600^oC and (2) co-evaporation of Mn during the host material growth. Using both methods, Mn was incorporated by replacing 20% of Mg without structural change. RHEED and XRD did not reveal the existence of additional phases. A more detailed investigation by TEM is in progress. Magnetic properties are studied by VSM, SQUID, and magnetotransport measurements.

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