Ferromagnetic semiconductors have recently received much interest, since they hold out prospects for using electron spins in electronic devices. Particulary GaMnAs has become the focus of current investigation because of its high Curie temperature.

The aim of present paper is to determine an influence of annealing under enhanced stress on the defect structure of GaMnAs. Ga_1-xMn_xAs (0.05<x<0.1) layers of 0.3-0.8 mm thickness were grown on GaAs (001) substrates by molecular beam epitaxy (MBE). Next the samples were treated at 700 K (HT) under enhanced Ar hydrostatic pressure (HP, equal to 1.1 GPa) for 1 h. Structural investigations were carried out using X-Ray MRD-PHILIPS diffractometer in the double (DAD) and triple (TAD) axis configurations as well as by Secondary Ions Mass Spectroscopy (SIMS). The rocking curves and reciprocal space maps were recorded. Lattice parameters of the layers were determined from the symmetrical and asymmetrical X-Ray reflection. The Mn concentration, the lattice parameters of the layer as well as the strain state before and after processing were calculated.

The total concentration of Mn measured by SIMS method remained unchanged after the treatment. However, drastic decrease of the out-of-plane lattice parameter was detected. These treatment - induced changes depend strongly on the Mn concentration. For Mn concentration about 10 %, the diffraction peak coming from the layers disappears, while the detectable interference fringes as well as the SIMS results show that the thickness of the thin layer as well as Mn concentration remain unchanged. It has been found that post - growth annealing of GaMnAs under high pressure leads to the lattice constant contraction, more pronounced than that caused by annealing under 10⁵ Pa. The rocking curve width (FWHM), layer thickness and lattice constant of the GaAs substrate remained unchanged after the treatment. Contraction of the lattice parameter can be related to the decreased concentration of interstitial Mn atoms and/or of arsenic antisites. The contribution of arsenic antisites and of Mn atoms, both substitutional and interstitial, to the a_GaMnAs value is given by the formula (compare [1]).

a_GaMnAs (x,y,z) = a₀ + 0.02x + 0.69y + 1.05z

where: a₀ - lattice constant of defects - free GaAs, y - concentration of As antisites, z - concentration of Mn in the interstitial positions. Possible structure change of GaMnAs from the cubic to hexagonal one [2] was also accounted for. The reason for stress - induced effects in GaMnAs layers has been discussed.

References

1. J. Masek, J. Kurdnowsky, F. Maca, Phys. Rev. B 67, 153203 (2003).
2. V. M. Kaganer, B. Jenichen, F. Schipan, W. Braun, L. Daweritz, K. H. Ploog, Phys. Rev. B 66, 045305 (2002).

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