Ferromagnetic (Ga,Mn)As Layers and ... - OPUS Würzburg

68 5. Local Anisotropy Control by Strain Engineering
6.00
(a)
GaAs
(b)
5.98
(Ga,Mn)As
[00L]
5.96
(In,Ga)As
5.94
1.98 2.00 2.02
[0H0]
1.98 2.00 2.02
[H00]
Figure 5.4: HRXRD measurement of sample B, showing a reciprocal space map of the
(026) and (206) Bragg reflection with incident x-rays (a) perpendicular and (b) parallel to
the stripe axis. The red line indicates the triangle of relaxation for (In,Ga)As for uniaxial
relaxation.
we attribute the bulge marked with orange ovals below the substrate peak in Fig. 5.4
(a) and (b) to the (Ga,Mn)As layer. By estimating its peak position in the RSM in
Fig. 5.4 (a) at (1.992, 5.988), we conclude, that tensile strain in the range of e [010] =
(2.2 ± 1.0) × 10 −3 has been induced in the (Ga,Mn)As layer by the underlying stressor.
This value is in good agreement with the finite element simulations which predict a
value e [010] = 1.47 × 10 −3 for this sample.
HRXRD RSM, [1¯10] Stripes
For [1¯10]-aligned stripes, the situation is slightly different than in the previous measurement.
Lattice planes of asymmetric reflexes with h = k are now oriented along the
direction parallel and perpendicular to the stripe axis. For this reason we chose the
(113) Bragg reflection for the measurement of sample C shown in Fig. 5.5. Both maps
are qualitatively very similar to the maps measured for [100] stripes. For incident
x-rays perpendicular to the stripes (Fig. 5.5 (a)), we observe a shift of the stressor
layer peak along the relaxation line, caused by lattice expansion in [110] direction. For
x-rays parallel to the stripes, no change in q ‖ is visible, which proves that the lattice
of both top layers remains pseudomorphic to the substrate in this direction, as it did
in the corresponding case for the [100] stripes.
As predicted by the finite element simulations, the overall strain relaxation is