Abstract
We investigate spin-dependent interband tunnelling in a ferromagnetic (Ga,Mn)As/ GaAs Zener diode. The ferromagnetic pn-junction is fabricated with a Mn-doped p-type GaAs layer on top of a nonmagnetic n-type GaAs substrate. When both sides of the junction are heavily doped, a large magnetic-field–dependent tunnelling effect can be seen at low temperatures in the measured current-voltage (I-V) characteristics. A model for the tunneling current in a ferromagnetic Zener diode is presented, and the observed effects are explained by the exchange interaction related splitting of the valence band states in (Ga,Mn)As. To our knowledge, this is the first time the effect of the band splitting and a large magnetoresistance related to the tunnelling processes have been observed experimentally in the I-V characteristics of a ferromagnetic Zener diode.