With the development of epitaxial growth technology such as molecular beam epitaxy (MBE), a variety of semiconductor heterostructures are now grown with atomically controlled layer thicknesses and abrupt doping profiles. Such growth technique has made it possible to design magnetic semiconductor heterostructures, in which the wavefunction of carriers can be controlled in artificially designed potentials [1,2]. We found that in appropriately designed p-type AlGaAs/GaAs heterostructures with Mn delta-doping, the increase of the Mn dopant concentration and maximizing the overlap of the Mn local spins with holes led to significant enhancement of TC up to 172-250 K [2,3]. In this paper, we review our study on the magnetotransport properties and Curie temperature of ferromagnetic III-V semiconductor heterostructures (Mn delta-doped GaAs/p-AlGaAs heterostructures).
It was recently revealed that (Ga,Mn)As epilayers have a cubic magnetic anisotropy with the easy axis of <100> at low temperature [4] and showed a change to the uniaxial anisotropy with the easy axis of [110] with increasing temperature [5]. We present our recent results on the giant planer Hall effect (PHE) and magnetic anisotropy of Mn δ-doped GaAs/p-AlGaAs heterostructures [6]. The sample structure is (from the surface to the substrate) GaAs(2nm) / Be-doped Al0.8Ga0.2As(15nm) / GaAs(2nm) / Mn delta-doped(0.75ML) /GaAs(20nm) / Al0.8Ga0.2As(15nm) / GaAs(200nm) / GaAs(001) substrate. We performed systematic investigations of PHE, including its temperature dependence and angular dependence. The heterostructures show distinct in-plane uniaxial anisotropy along [110].
[1] A. M. Nazmul et al., Appl. Phys. Lett. 80, 3120 (2002). [2] A. M. Nazmul et al., Phys. Rev. B 67, 241308 (2003). [3] A. M. Nazmul et al., Phys. Rev. Lett. 95, 017201 (2005). [4] H. X. Tang et al., Phys. Rev. Lett. 90, 107201 (2003). [5] U. Welp et al. Phys. Rev. Lett. 90, 167206 (2003). [6] H. T. Lin et al., submitted.

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