Low Temperature Annealing Studies of Ga1−xMnxAs

High and low field magnetotransport measurements, as well as SQUID measurements of magnetization, were carried out on Ga1−xMnxAs epilayers grown by low temperature molecular beam epitaxy, and subsequently annealed under various conditions. We observe a large enhancement of ferromagnetism when the samples are annealed at an optimal temperature, typically about 280°C. Such optimal annealing leads to an increase of Curie temperature, accompanied by an increase of both the conductivity and the saturation magnetization. A decrease of the coercive field and of magnetoresistivity is also observed for Ga1−xMnxAs annealed at optimal conditions. We suggest that the experimental results reported in this paper are related to changes in the domain structure of Ga1−xMnxAs.