We have observed very large tunneling magnetoresistance (TMR) in epitaxially grown ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}/\mathrm{AlAs}/{\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ ferromagnetic semiconductor tunnel junctions. Large TMR ratios more than $70\%$ (maximum $75\%$) were obtained in junctions with a very thin ( $\le 1.6\mathrm{nm}$) AlAs tunnel barrier when the magnetic field was applied along the $\left[100\right]$ axis in the film plane. The TMR was found to rapidly decrease with increasing barrier thickness, which is explained by calculations assuming that the parallel wave vector of carriers is conserved in tunneling.

• Received 5 January 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.026602