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In diluted magnetic III-V compound semiconductors such as Mn-doped GaAs a metal-insulator (MI) transition is observed, when the Mn consentration is increased above 3%. We have succeeded in the fabrication of magnetic Schottky diodes, when using a p-type Mn-doped GaAs and choosing the Mn concentration on the semiconducting side of the MI-transition. The Mn-doped GaAs thin films were grown on p-type GaAs substrates by using Molecular Beam Epitaxy technique. The Schottky contacts on top of the (Ga,Mn)As layer were made of Pt metal by using an e-beam evaporation. The ohmic contacts on the back side were made of an Au/Ge/Ni alloy. For comparison, we also fabricated non-magnetic GaAs Schottky diodes, where, instead of the Mn doping, beryllium was used as a p-type dopant. In the characterization of the Schottky diodes first the magnetotransport properties of the Mn-doped layer without a Schottky contact were studied by performing resistivity, magnetoresistance (MR), and Hall measurements. The observed anomalous Hall effect indicates that even the semiconducting Mn-doped layers are ferromagnetic at low temperatures T<30 K. In the same layer a large negative MR was observed at low temperatures. The contributions to the MR from the shift of the mobility edge and a swelling of the orbits of the localized states below the mobility edge are estimated quantitatively. Next the I-V characteristics of both the magnetic and non-magnetic Schottky diodes were measured in a wide temperature range as a function of an external magnetic field. In contrast to the non-magnetic GaAs Schottky diodes, a large negative MR in the dc current was observed in the magnetic diodes at low temperatures. The contributions from the spin dependent tunnelling through the thin Schottky barrier and the negative MR of the semiconducting layer are discussed in detail. |