Tunneling spectroscopy and tunneling magnetoresistance in (GaMn)As ultrathin heterostructures

We have studied tunneling spectroscopy of two types of ultrathin magnetic semiconductor heterostructures; Au/Al2O3/(GaMn)As, and (GaMn)As/AlAs/(GaMn)As. The latter is all MBE grown heterostructures with abrupt and smooth interfaces and atomically controlled barrier thickness. It was found that (GaMn)As has a small energy gap, which is similar to the soft Coulomb gap, near the Fermi energy, like heavily doped semiconductors. Temperature dependence of the tunneling conductance, which is proportional to the transverse density-of-state of the electrode, follows the power law T-0.5. Furthermore, large tunneling magnetoresistance (TMR) was observed in a (GaMn)As/AlAs/(GaMn)As tunnel junction. (C) 1999 Elsevier Science B.V. All rights reserved.