Calculation of the electron mobility and spin lifetime enhancement by strain in thin silicon films

Spintronics attracts much attention because of the potential to build novel spin-based devices which are superior to nowadays charge-based microelectronic devices. Silicon, the main element of microelectronics, is promising for spin-driven applications. Understanding the details of the spin propagation in silicon structures is a key for building novel spin-based nanoelectronic devices. We investigate the surface roughness-limited electron mobility and spin relaxation in a silicon spin field-effect transistor. Shear strain dramatically influences the spin relaxation, which opens a new opportunity to boost spin lifetime in a silicon spin field-effect transistor. Introduction Spintronics is the rapidly developing and promising technology exploiting spin properties of electrons. A number of potential spintronic devices has been proposed [1–3]. Since silicon is the basic material used for manufacturing modern MOSFETs, developing silicon-based nanoelectronic devices utilizing spin properties is promising. Silicon is an ideal material for spintronic applications, because it is composed of nuclei with predominantly zero spin and is characterized by small spin-orbit coupling. Both factors favour a small spin relaxation. However, large spin relaxation rates in gated silicon structures have been experimentally observed. Understanding the details of the spin propagation in modern ultra-scaled silicon MOSFETs is urgently needed [4]. 1. Model We study electron scattering and spin relaxation processes dominated by surface roughness. The subband energies and wave functions were obtained from a k×p Hamiltonian [5,6] generalized to include the spin degree of freedom [4,7]. The Hamiltonian is written in the vicinity of the X-point along the kz-axis in the Brillouin zone and includes the two relevant valleys of the conduction band [8]. After a unitary basis transformation it is written as H = [ H1 H3 H3 H2 ] , (1) with H1,2 = ⎡⎣ h̄2k2 z 2ml + h̄2 ( k2 x+k y ) 2mt +U(z)+(−1)j δ ⎤⎦ I, (2) H3 = [ h̄k0kz ml 0 0 h̄ k0kz ml ]