Nano and Giga Challenges in Microelectronics, Cracow, 2004 Spin Injection in Semiconductor Nanostructures Alexey Toropov Ioffe Institute, St.Petersburg, Russia Nano and Giga Challenges in Microelectronics, Cracow, 2004OUTLINE * Brief historical introduction, motivation * Different approaches proposed to create spin-polarized carriers in semiconductors * Spin-dependent resonant tunneling in diluted magnetic semiconductor heterostructures (DMS) for spin injection and spin manipulation - In-depth optical studies of spin functionality in II-VI DMS - Hybrid III-V / II-VI DMS heterostructures spin- dependent resonant tunneling through a III-V / II-VI heterovalent interface Nano and Giga Challenges in Microelectronics, Cracow, 2004 SPIN INJECTION IN SEMICONDUCTORS A. G. Aronov, G. E. Pikus Spin injection appears when the current flows through a ferromagnetic-semiconductor contact. Depending on the type of the contact, either majority or minority carriers can be polarized. The magnetic field effect on the spin injection and possible experimental conditions are discussed. Nano and Giga Challenges in Microelectronics, Cracow, 2004 First realization of the spin transistor? K. Yoh et al., PASPS III (2004), ICPS27 (2004) Hokkaido Uni./JST/Stanford Uni./Uni. of Michigan From spin transistor to spin quantum computer.. Nano and Giga Challenges in Microelectronics, Cracow, 2004 Spin-polarized carriers in semiconductors - Spin injection from metals - Spin injection and manipulation in diluted magnetic semiconductors (DMS) III-V compounds II-VI compounds Wide-band-gap semiconductors (ZnO:Mn,Co..; GaN:Mn) - Spin polarization in non-magnetic semiconductors, Rashba effect Nano and Giga Challenges in Microelectronics, Cracow, 2004 Ferromagnetic metal versus diluted magnetic semiconductor : numerous fruitless attempts to inject spins from ferromagnetic metals (Fe, Co,) to semiconductors. Schmidt, et al., Phys. Rev. B (2000): metal-semiconductor spin injection is impossible due to the large conductivity mismatch. Fiederling, et al., Nature (1999): Successful spin injection (~80%) from a DMS semiconductor into a GaAs/AlGaAs light-emitting diode (LED) Nano and Giga Challenges in Microelectronics, Cracow, 2004 Ferromagnetic metals Rashba, Phys. Rev. B (2000): the metal-semiconductor conductivity mismatch problem can be overcome by injecting spins through a tunnel Schottky barrier Zhu et al, Phys. Rev. Lett (2001): Fe/GaAs interface, 2% injection efficiency Hanbicki et al, Appl. Phys.Lett (2002): Fe/AlGaAs interface, 30% injection efficiency (240K) Vant Erve et al, Appl. Phys.Lett (2004): Fe/Al 2 O 3 /GaAs interface, 40% injection efficiency Problems : - limit current through a tunnel barrier - difficult formation of the high quality metal-semiconductor interface K. Yoh et al, (2004): up to 12% efficiency of the spin injection from Fe to InAs without any tunnel barrier! Nano and Giga Challenges in Microelectronics, Cracow, 2004 Ferromagnetic metals seem currently most promising for room temperature spin injection applications Advantages of DMS are: - Better technological compatibility with semiconductor electronics and optoelectronics; - Efficient electrical, optical and strain control over magnetization (sign reversal, easy axis rotation,..); - New spin functionalities (spin-dependent resonant tunneling [Waag et al., 2001 ], spin-relaxation engineering [Hall et al., 2003],..).Summarizing.. Nano and Giga Challenges in Microelectronics, Cracow, 2004 Diluted magnetic semiconductors II-VI DMS (ZnMnSe, CdMnTe, ): - Unlimited solubility of Mn giant spin splittings are available - Perfect optical quality advantages of optical spectroscopy - Both n- and p-type doping is available BUT - Very small Curie Temperature Tc0, g h