High-resolution X-ray diffraction results: 2θ/ω scans for (004) Bragg reflections for LT-GaAs and (Ga,Mn)As epitaxial layers grown on (001) semi-insulating GaAs substrate. The curves have been vertically offset for clarity. The narrow line corresponds to reflection from the GaAs substrate and the broader peaks at lower angles are reflections from the layers. With increasing Mn content the (Ga,Mn)As diffraction peaks shift to smaller angles with respect to that of the LT-GaAs reference layer.
Raman spectra recorded at room temperature in backscattering configuration from the (001) surfaces of the LT-GaAs reference layer and four (Ga,Mn)As layers, where full symbols represent experimental data. The spectra have been normalized to the same intensity. The three lower spectra have been decomposed into two components of the TO- and LO-phonons, shown with solid lines. The two upper spectra have been decomposed into three components of the TO- and LO-phonons (solid lines) and the CPLP mode (cross-hatched area).
Modulation photoreflectance spectra for the LT-GaAs reference layer and four (Ga,Mn)As layers with various Mn contents epitaxially grown on GaAs substrate (dots), where the FKOs extrema are marked with numbers. The spectra have been normalized to the same intensity and vertically offset for clarity. Solid lines represent fits to the experimental data by full-line-shape analysis of the spectra.
Analysis of the period of Franz-Keldysh oscillations revealed in the PR spectra for the LT-GaAs reference layer and four (Ga,Mn)As layers with various Mn contents.
Schematic energy band diagram for LT-GaAs (a) and its evolution for (Ga,Mn)As with increasing Mn content of 0.005% (b) and 1.2% (c). Splitting of the bands in the ferromagnetic state is omitted for simplicity. Arrows indicate electronic transitions from the valence band to the conduction band. MnGa-related impurity band is assumed to be merged with the GaAs valence band in (b) and (c). In p-type (Ga,Mn)As the Fermi level position, determined by the free-hole concentration, lies within the valence band and the absorption edge shifts from the center of the Brillouin zone to the Fermi-wave vector, as shown in (c).
Layer thicknesses and their lattice parameters, c and a rel, lattice mismatch (defined as (a rel − a sub)/a sub, where a sub = 5.65349 Å is the lattice constant of GaAs substrate), and vertical strain (defined as (c − a rel)/a rel) for the investigated layers calculated from the results of high-resolution XRD measurements performed at 27 °C.
The values of transition energies E0 and electro-optic energies for light and heavy holes, ℏθlh and ℏθhh , respectively, obtained from the full-line-shape analysis of the PR spectra shown in Fig. 3 , and the values of energies EG and electro-optic energies ℏθ, obtained from the analysis of the FKOs period shown in Fig. 4 .
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