ABSTRACT

Spintronics is an emerging approach toward novel computing devices, which takes advantage of the spin degree of freedom in addition to the electric charge of electrons [1]. The variety of spin logic devices described in Chapter 17 illustrates the intriguing possibility of building scalable energy-efficient devices using the spin of electrons. However, efficient spin injection and long spin diffusion length in the channel of a spin-field-effect-transistor (FET) are the two major challenges inherent in all spin-FETs. When injected into a semiconductor channel, the spins of conduction electrons are subject to different relaxation mechanisms (e.g., Elliott [2]; D’yakonov and Perel’ [3]; Bir et al. [4]), which reduce the spin polarization (see Chapter 1, Volume 2, of this book for a detailed discussion of these relaxation mechanisms). All scattering mechanisms tend to equalize the number of spin up and spin down electrons in a non-magnetic semiconductor channel. In turn, the variation of the spin polarization among the ensemble of conducting electrons reduces the on/off ratio. In the best case scenario, materials with high mobility and low scattering (e.g., graphene) show electron spin diffusion length on the order of several micrometers at room temperature [5].