Article

Achieving High Curie Temperature in (Ga,Mn)As

Applied Physics Letters (Impact Factor: 3.79). 08/2008; DOI: 10.1063/1.2992200
Source: arXiv

ABSTRACT We study the effects of growth temperature, Ga:As ratio and post-growth annealing procedure on the Curie temperature, Tc, of (Ga,Mn)As layers grown by molecular beam epitaxy. We achieve the highest Tc values for growth temperatures very close to the 2D-3D phase boundary. The increase in Tc, due to the removal of interstitial Mn by post growth annealing, is counteracted by a second process which reduces Tc and which is more effective at higher annealing temperatures. Our results show that it is necessary to optimize the growth parameters and post growth annealing procedure to obtain the highest Tc.

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    ABSTRACT: The dilute (Ga,Mn)As became a model ferromagnetic semiconductor, however there is still a disagreement on the source of its magnetism. In this paper, we verify the ellipsometric results and compare them with more precise photoreflectance method, which gives an important insight into the interaction of the Mn-related states with the ones of GaAs valence band. No spectral shifts observed for the E1 and E1þD1 interband transitions in highly doped and annealed (Ga,Mn)As epitaxial layers indicate that the coupling between a detached Mn impurity band and the valence band does not occur. Our findings are supported by the characterizations of the (Ga,Mn)As epitaxial layers with the high resolution transmission electron microscopy and magnetization measurements.
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    ABSTRACT: The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results revealing a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy in the annealed (Ga,Mn)As layers is interpreted as a result of the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the enhanced free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.
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    ABSTRACT: The diluted (Ga,Mn)As became a model ferromagnetic semiconductor, however there is still a disagreement on the source of its magnetism. The divergences arise from the results indicating that the holes mediated ferromagnetism reside in the valence band or the impurity band. Full understanding of character of the Mn states in GaAs can bring the increase of (Ga,Mn)As Curie temperature. In this paper we verify the ellipsometric results and compare with more precise photoreflectance method which gives a new insight into the interactions of Mn impurity states with GaAs valence band. Indeed, E1 and E1+Δ1 inter-band transition energies for highly doped and annealed (Ga,Mn)As epitaxial layers have not confirmed the interaction between detached Mn impurity band and the valence band. Thus, the description with merged Mn states and GaAs valence band is in agreement with our results. Our findings are supported by the high resolution transmission microscopy and magnetization measurements.

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May 20, 2014