Epitaxie und Charakterisierung semimagnetischer Heterostrukturen auf Basis von GaMnAs

Abstract

This work describes the epitaxy and characterisation of the ferromagnetic semiconductor GaMnAs, single layers as well as superlattices.

The effect of the V/III flux ratio and substrate temperature on the magnetotransport properties and lattice parameters of Ga0.96Mn0.04As grown by molecular beam epitaxy have been studied. The Curie temperature as high as 95 K was achieved for the Ga0.96Mn0.04As samples grown at 240°C and a V/III ratio of about 1.5. The lattice parameter of Ga0.96Mn0.04As increased with decreasing V/III ratio and/or increasing growth temperature. Possible reasons for the effect of V/III ratio on the magnetotransport properties and lattice parameter of GaMnAs are discussed.

Detailed investigations of the electronic and magnetic properties of ferromagnetic GaMnAs layers have been performed. Superconducting quantum interference device measurement reveal a decrease of the Curie temperature from the surface to the GaMnAs/GaAs interface.While high resolution x-ray diffraction clearly hows a homogeneous Mn distribution,a pronounced decrease of the carrier concentration from the surface towards the GaMnAs/GaAs interface has been found by Raman spectroscopy as well as by electrochemical capacitance-voltage processing.

The enhancement of the Curie temperature in GaMnAs/InGaMnAs heterostructures, which is due to thin InGaMnAs or InGaAs embedded into the GaMnAs layers have been discussed. The pronounced increase of the Curie temperature is strongly correlated to the Inconcentration in the embedded layers. Curie temperatures up to 110K are observed in such structures compared to 60K in GaMnAs single layers grown under the same conditions.A further increase in T C up to 130 K can be achieved using post-growth annealing at temperatures near the growth temperature.