Fachgruppe Nanostrukturierte Materialien    

The incorporation of carbon in low-temperature (LT) GaAs and GaMnAs layers deposited by molecular-beam epitaxy under various growth conditions has been investigated. The lattice parameter depends on Mn content, C content, and the growth conditions which strongly affect Mn, C, and point defect incorporation. We found optimum growth conditions (, the beam equivalent pressure ratio is 5, growth rate is ) at which high-quality GaMnAs layers with moderate Mn content as well as LT-GaAs layers were deposited, which were efficiently p-doped by carbon. LT GaAs:C revealed the same electrical activation of carbon of about 50% at a high doping level as observed in high-temperature GaAs:C. The Curie temperature as well as the saturation magnetization of GaMnAs decreases with Cdoping. This suggests a reduced amount of Mn contributing to the ferromagnetic phase in GaMnAs:C.