Electrical transport in Mn-doped GaAs pn-diodes

We have studied the effect of magnetic ordering on the electrical transport in magnetic GaAs diodes. The fabricated pn-junctions consist of Mn-doped ferromagnetic layers on top of non-magnetic semiconductor substrates. First the electrical and magnetic properties of the magnetic layers are investigated, which shows that the exchange interaction between the charge carriers and the localized magnetic moments of the Mn-atoms dominates the charge transport at temperatures close to the Curie temperature. In the GaxMn1-xAs/GaAs-p(++)n(++)-junctions having heavily doped p- and n-regions, the inter-band tunnelling current shows large dependence on the magnetic ordering. The spin-dependent tunnelling can be explained by a model, where the density of valence band states decreases due to the band splitting caused by the exchange interaction. From the measured decrease of the tunnelling current we estimated the value for the exchange parameter J(exch)(pd) = 2.9 eV. Various explanations for the absence of magnetoresistance in the magnetic diodes with lightly doped non-magnetic regions are discussed. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.