Spin injection into semiconductors: the role of the Fe/Al/sub x/Ga/sub 1-x/As interface

The influence of the growth and post-growth annealing temperatures of Fe/Al/sub x/Ga/sub 1-x/As-based spin light-emitting diodes (LEDs) on the spin injection efficiency is discussed. The extent of interfacial reactions during molecular beam epitaxial growth of Fe on GaAs was determined from in-situ X-ray photoelectron spectroscopy studies. The Fe/GaAs interface results in /spl les/ 3 monolayers of reaction for Fe grown at -15 /spl deg/C. Intermediate growth temperatures (95 /spl deg/C) lead to /spl sim/5 monolayers of interfacial reactions, and high growth temperatures of 175 /spl deg/C lead to a /spl sim/9 monolayer thick reacted layer. Polarized neutron reflectivity was used to determine the interfacial magnetic properties of epitaxial Fe/sub 0.5/Co/sub 0.5//GaAs heterostructures grown under identical conditions. No interfacial magnetic dead layer is detected at the interface for Fe/sub 0.5/Co/sub 0.5/ films grown at -15 /spl deg/C, a /spl sim/6 /spl Aring/ thick nonmagnetic layer formed at the interface for 95 /spl deg/C growth and a /spl sim/5 /spl Aring/ thick magnetic interfacial reacted layer formed for growth at 175 /spl deg/C. Spin injection from Fe contacts into spin LEDs decreases sharply when reactions result in a nonmagnetic interfacial layer. Significant spin injection signals are obtained from Fe contacts grown between -5 /spl deg/C and 175 /spl deg/C, although the higher Fe growth temperatures resulted in a change in the sign of the spin polarization. Post-growth annealing of the spin LEDs is found to increase spin injection efficiency for low Fe growth temperatures and to a sign reversal of the spin polarization for high growth temperature (175 /spl deg/C). An effective Schottky barrier height increase indicates that post growth annealing modifies the Fe/Al/sub x/Ga/sub 1-x/As interface.