Direct observation of the barrier asymmetry in magnetic tunnel junctions

Abstract

A photoconductance method has been used to study directly the barrier asymmetry in TaOx magnetic tunnel junctions. Due to optical electron-hole pair generation in the barrier itself and subsequent transport in the elec. field, the sign and magnitude of the barrier asymmetry can be detd. quite accurately. The reliability of the technique is demonstrated by the independence on the direction of illumination. The oxidn. time where the asymmetry becomes zero is found to coincide with a max. in the magnetoresistance ratio. This is argued to be due to the complete oxidn. of the barrier material, resulting in a sym. tunnel barrier. [on SciFinder (R)