We have investigated Fe/InAs interfaces for two different growth temperatures of Fe and the effect on the spin injection properties through an Fe/InAs junction. Secondary ion mass spectroscopy and transmission electron microscopy studies of the Fe/InAs interfaces revealed that Fe films grown at 175 degreesC clearly suffer from increased reaction and out-diffusion of semiconductor constituents compared to those grown at 23 degreesC. The lower temperature samples showed an increased degree of spin polarization of 18%-20% which translates to 36%-40% of spin injection efficiency assuming selection rules between heavy and light holes in the p-type InAs substrate. It is close to the spin polarization of 40%-45% in an Fe spin injector itself. (C) 2004 American Vacuum Society.