  Spin injection efficiency based on conventional and/or half-metallic
ferromagnet/semiconductor is greatly limited by the Schmidt obstacle due to
conductivity mismatch, here we proposed that by replacing the metallic
injectors with spin gapless semiconductors can significantly reduce the
conductive mismatch to enhance spin injection efficiency. By performing first
principles calculations based on superlattice structure, we have studied the
representative system of Mn2CoAl/semiconductor spin injector scheme. The
results showed that a high spin polarization was maintained at the interface in
systems of Mn2CoAl/Fe2VAl constructed with (100) interface and Mn2CoAl/GaAs
with (110) interface, and the latter is expected to possess long spin diffusion
length. Inherited from the spin gapless feature of Mn2CoAl, a pronounced dip
was observed around the Fermi level in the majority-spin density-of-states in
both systems, suggesting fast transport of the low-density carriers.
