Abstract
We investigate the electronic and magnetic properties of ferromagnetic GaMnAs single layers as well as multilayer structures fabricated by low-temperature molecular beam epitaxy. The electrochemical capacitance–voltage profiling as well as Raman spectroscopy measurements in GaMnAs single layers reveal a vertical gradient in the carrier concentration and therefore a gradient in Curie temperature measured by superconducting quantum interference device. Detailed studies of carrier density and ferromagnetic transition before and after annealing of the layers are presented. We also report on an enhancement of the Curie temperature in GaMnAs / InGaMnAs superlattices, which is due to thin InGaMnAs or InGaAs films embedded into the GaMnAs layers. The pronounced increase of the Curie temperature is strongly correlated to the In concentration in the embedded layers. Curie temperatures up to 110 K are observed in such structures compared to 60 K in GaMnAs single layers grown under the same conditions. A further increase in TC up to 130 K can be achieved using post-growth annealing at temperatures near the growth temperature.
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