Short-period (Ga,Mn)As/(Al,Ga)As multilayer structures studied by cross-sectional scanning tunneling microscopy

(Ga_1-x,Mn_x)As/GaAs and (Ga_1-x,Mn _x)As/(Al_0.2,Ga_0.8)As multilayer structures grown by molecular beam epitaxy have been studied by cross-sectional scanning tunneling microscopy. These dilute magnetic semiconductor multilayer structures have been predicted to have a strong giant magnetoresistance effect and enhanced Curie temperature. However, a sharp and short-period digital doping profile of the Mn acceptors is essential to achieve this, and therefore the studied samples were grown at a low growth temperature (250 C). Cross-sectional scanning tunneling microscopy measurements show that the overall quality of the structure is good but many As antisites are present due to the low growth temperature. The observed Mn profile showed that, despite the low growth temperature, about 20% of the Mn acceptors from the doped layers (eight monolayers thick) end up in the nominally undoped spacer layers (four monolayers thick). This segregation puts serious constraints on the creation and application of short-period dilute magnetic superlattices because of the magnetic shortcut caused by the Mn acceptors in the spacer layer.