Room Temperature Spin Injection

Spintronics is the fledgling technology in which an electron's spin orientation, and not just its electrical charge, is used as a way of controlling or storing information. As part of this process, droves of polarized electrons (a majority of electrons having the same spin direction) must be created and moved across various metal and semiconductor frontiers.

Scientists at the Paul-Drude Institute in Berlin have now, for the first time, sent polarized electrons from a metal (Fe) into a semiconductor (GaAs) at room temperature. The spin injection efficiency is only 2%, not good enough for doing spintronics, but impressive nevertheless considering that some researchers have found a "dead zone" between the iron and GaAs layers, seemingly precluding any orderly transmission of electron spin. Injection efficiencies as high as 30% have been achieved from a metal but only for scanning tunneling microscopy experiments, where practical applications are not likely to develop.

The Berlin researchers (Manfred Ramsteiner, 49-30-20377-338, mer@pdi-berlin.de) know that some of the net polarization survived intact since these spin-injected electrons, moving further into a sandwich of semiconductor layers constituting a quantum well, combine with holes to create polarized light. (Zhu et al., upcoming article in Physical Review Letters; text at Physics News Select.

Another spintronics development comes in the form of a continuous supply of polarized electrons. David Awschalom at UCSB has succeeded in injecting a steady current of spins (at a temperature of 5 K) from one semiconductor layer (GaAs) into another (ZSe) with the help of an applied voltage. (Malajovich et al., Nature, 14 June 2001.)