ABSTRACT
Abstract. A large tunneling magnetoresistance was observed in epitaxial hybrid magnetic tunnel junctions composed of MnAs/AlAs/GaMnAs. The low temperature current-voltage characteristics were in accord with those of a tunneling process through an asymmetric barrier. These experiments confirm that efficient spin injection from metals into semiconductors is possible when a suitable tunnel barrier is used. 12
1. Introduction The injection of a spin-polarized current into semiconductors is a key requirement for the success of semiconductor spintronics. Efficient spin injection has been anticipated and demonstrated using ferromagnetic semiconductors [1] and highly spin-polarized paramagnetic semiconductors [2]. However, for future devices operating at room temperature, it is desirable to use metallic ferromagnets as a source of spin-polarized current. A critical problem is the large conductivity mismatch, which prohibits efficient spin injection from metallic ferromagnets into semiconductors. Recently, spin injection through a tunnel barrier was proposed as a way to circumvent this problem [3]. To test this idea, we have fabricated metal-semiconductor hybrid magnetic tunnel junctions (MTJ) with different tunnel barrier strengths (MnAs/AlAs/GaMnAs) and measured tunneling magnetoresistances (TMR). Indeed more than 30 % TMR is observed when the barrier strength is optimized. This suggests that MnAs/AlAs heterostructures offer well characterized tunnel junctions for high efficiency spin injection into semiconductors.
