Spin injection from a ferromagnet into a semiconductor in the case of a rough interface

The effect of the interface roughness on the spin injection from a ferromagnet into a semiconductor is studied theoretically. Even a small interface irregularity can lead to a significant enhancement of the injection efficiency. When a typical size of the irregularity, a, is within a domain lambda_F << a << lambda_N, where lambda_F and lambda_N are the spin-diffusion lengths in the ferromagnet and semiconductor, respectively, the geometrical enhancement factor is ~lambda_N. The origin of the enhancement is the modification of the local electric field on small scales ~a near the interface. We demonstrate the effect of enhancement by considering a number of analytically solvable examples of injection through curved ferromagnet-semiconductor interfaces. For a generic curved interface the enhancement factor is ~lambda_N / R, where R is the local radius of curvature.