Investigation into the physical properties of the diluted magnetic semiconductor galliuma manganese arsenide

Over the past decade, a new field termed "spintronics" has emerged in which the spin of a particle rather then just its charge is used to process and store information. Diluted magnetic semiconductors may play a prominent role in this field, because they can be used to align spins and can be grown epitaxially within hetrostructures; however, current Curie temperatures are too low to make room temperature devices. This dissertation examines the possibility of improving the magnetic and transport properties of the diluted magnetic semiconductor Ga1-xMnxAs.; In our first study, low temperature annealing was found to significantly increase Tc. A variety of studies were performed in attempts to discern the mechanism by which this enhancement occurred. It was found that annealing leads to a complex interplay between the defects associated with the low temperature growth conditions of the epilayers and possibly a free surface in the material.; To test the several different theories of magnetism in diluted magnetic semiconductors, a series of Ga1-xMnxAs samples was grown spanning the possible range of Mn concentrations. The magnetic properties of annealed samples were consistent with mean-field models, but a decreasing magnetization contribution per Mn atom was found with increasing Mn concentration. The resulting magnetization deficit persisted to fields up to 3 T, which supports reports of antiferromagnetic Mn pairs in the material. Thin domain wall widths, modeled as Neel walls, were found to be constant over the range of Mn concentrations, which should facilitate device fabrication.; Finally, the prospects for further increases in the Tc of Ga1-xMnxAs have been considered. Tc is observed to increase with carrier concentration roughly as predicted by mean-field models. The high carrier concentrations that would be required for room temperature ferromagnetism in Ga1-xMnxAs suggest other diluted magnetic semiconductors may be needed to obtain Tc of 300 K. Because Ga 1-xMnxAs has been very well characterized; however, it remains a good system in which to explore novel devices and ideas.