Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As

The effect of annealing at 250 C on the carrier depth profile, Mn distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As layers with thicknesses > 200 nm, grown by molecular-beam epitaxy at low temperatures, is studied by a variety of analytical methods. The vertical gradient in hole concentration, revealed by electrochemical capacitance-voltage profiling, is shown to play a key role in the understanding of conductivity and magnetization data. The gradient, basically already present in as-grown samples, is strongly influenced by post-growth annealing. From secondary ion mass spectroscopy it can be concluded that, at least in thick layers, the change in carrier depth profile and thus in conductivity is not primarily due to out-diffusion of Mn interstitials during annealing. Two alternative possible models are discussed.Comment: 8 pages, 8 figures, to appear in Phys. Rev.

Anomalous behavior of spin wave resonances in Ga_{1-x}Mn_{x}As thin films

We report ferromagnetic and spin wave resonance absorption measurements on high quality epitaxially grown Ga_{1-x}Mn_{x}As thin films. We find that these films exhibit robust ferromagnetic long-range order, based on the fact that up to seven resonances are detected at low temperatures, and the resonance structure survives to temperatures close to the ferromagnetic transition. On the other hand, we observe a spin wave dispersion which is linear in mode number, in qualitative contrast with the quadratic dispersion expected for homogeneous samples. We perform a detailed numerical analysis of the experimental data and provide analytical calculations to demonstrate that such a linear dispersion is incompatible with uniform magnetic parameters. Our theoretical analysis of the ferromagnetic resonance data, combined with the knowledge that strain-induced anisotropy is definitely present in these films, suggests that a spatially dependent magnetic anisotropy is the most likely reason behind the anomalous behavior observed.Comment: 9 pages, including 6 figure