Abstract
Manganese doped IIโIVโV~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~3~As~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 ยฐC 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 ยฑ10%, Hall measurements at room temperature showed nโtype conduction (n = 4 ร 10^17^ โผ 3 ร 10^18^ cm^โ3^) in germanium rich samples and pโtype conduction (p = 8 ร 10^18^ โผ 2 ร 10^19^ cm^โ3^) in magnesium rich samples.
Two ways of manganese incorporation were tried on (111)B grown MgGeAs~2~: (1) inโsitu solid state reaction by annealing a manganese layer deposited on top of MgGeAs~2~ and (2) coโevaporation 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. (ยฉ 2007 WILEYโVCH Verlag GmbH & Co. KGaA, Weinheim)