Influence of the valley degeneracy on spin relaxation in thin silicon films

Semiconductor spintronics is a rapidly developing field with a potentially large impact on microelectronics. Using electron spin may help to reduce power consumption and increase computational speed of modern electronic circuits. Silicon is perfectly suited for spin-based applications: it is characterized by a weak spin-orbit interaction which should result in a long spin lifetime. However, recent experiments indicate the lifetime may get significantly reduced in gated structures. Thus, understanding the peculiarities of the subband structure and details of the spin propagation in surface layers and thin silicon films in presence of the spin-orbit interaction is urgently needed. We investigate the contribution of the spin-orbit interaction to the equivalent valley splitting and calculate the spin relaxation matrix elements by using a perturbative k·p approach. We demonstrate that the valley degeneracy strongly influences the spin relaxation matrix elements. Shear strain is an efficient concept to lift the valley degeneracy, which can considerably suppress the electron spin relaxation in silicon surface layers and thin films.