Ballistic spin injection spectroscopy of a (Ga,Mn)As spin Esaki diode

A p-type ferromagnetic semiconductor (Ga,Mn)As is one of the promising materials for spin injector by interband tunneling [1]. In this work, we investigated injection of spin-polarized electrons in a (Ga,Mn)As/n$^+$-GaAs Esaki diode (ED) by using a three-terminal device integrating a (Ga,Mn)As ED and a light emitting diode (LED), which allows us to apply bias voltages to the ED and LED independently. Electroluminescence polarization ($P_{\rm EL}$) from the LED was measured under the Faraday configuration as a function of bias voltages. The maximum $P_{\rm EL}$ of 32.4\% was observed when the valence electrons near the Fermi energy of (Ga,Mn)As are ballistically injected into the LED. The experimental results proved high spin polarization of valence electrons ($>85$\%) for 100 meV below the Fermi energy of (Ga,Mn)As. [1] M.~Kohda et al., Jpn. J. Appl. Phys. Part2 {\bf 40}, L1274 (2001); E.~Johnston-Halperin et al., Phys. Rev. B {\bf 64}, 041306(R) (2002); P.~Van Dorpe et al., Appl. Phys. Lett. {\bf 84}, 3495 (2004).