MBE growth of MgGeAs ₂:Mn on GaAs substrate

Manganese doped II-IV-V ₂ chalcopyrites are promising candidates for room temperature ferromagnetic semiconductors. In this category, we report a new material MgGeAs ₂ :Mn for MBE growth on GaAs substrates. Firstly, we investigated the growth of MgGeAs ₂ 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 Mg ₃As ₂ and columnar grains with composition modulation. On GaAs(111)B, we obtained single crystalline films of 35 nm with a smooth surface at an optimized growth temperature of 560°C and a beam equivalent pressure ratio Mg:Ge:As = 1:3.1:800. The lattice constant of the chalcopyrite phase is nearly matched to GaAs for both (001) and (111)B growth, in contrast to the theoretical prediction of a 6.1% mismatch. With flux variations of ±10%, Hall measurements at room temperature showed n-type conduction (n = 4 × 10 ¹⁷ - 3 × 10 ^-8 cm ^-3) in germanium rich samples and p-type conduction (p = 8 × 10 ¹⁸ × 2 × 10 ¹⁹ cm ^-3) in magnesium rich samples. Two ways of manganese incorporation were tried on (111)B grown MgGeAs ₂: (1) in-situ solid state reaction by annealing a manganese layer deposited on top of MgGeAs ₂ and (2) co-evaporation of manganese during the host material growth. Using method (2), manganese was incorporated by replacing 20% of magnesium without structural change. RHEED and XRD did not reveal the existence of additional phases. However, the preliminary magnetization and transport measurement didn't reveal a ferromagnetic signal in these samples.