Regensburg 2010 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 61: Poster II: Materials, Interfaces and Heterostructures

HL 61.19: Poster

Thursday, March 25, 2010, 18:00–20:00, Poster D1

Ab initio study of strain effects on the quasiparticle bands and effective masses in silicon — •Mohammed Bouhassoune and Arno Schindlmayr — Department Physik, Universität Paderborn, 33095 Paderborn, Germany

Strain engineering has emerged as a promising technology to improve the performance of silicon-based MOSFETs. In general, strain influences the carrier mobility and hence the switching times by two mechanisms: a partial lifting of band-edge degeneracies, which reduces the scattering rate, and modified effective masses due to band warping. For monoclinic deformations along the [110] direction, which have attracted particular interest, experimental evidence suggests that both factors contribute to the observed high electron mobility in n-doped samples. In order to assess their relative importance, we study the electronic properties of silicon under uniaxial and biaxial [110] strain quantitatively with ab initio computational methods. For this purpose we combine density-functional theory in the local-density approximation with the GW approximation for the electronic self-energy, which gives a highly accurate description of the quasiparticle band structure. The elastic constants, Poisson ratios and related structural parameters are determined with full volume and internal relaxation from the variation of the total energy. Then we calculate the energy splitting of the six originally degenerate conduction-band minima and the electron effective masses as a function of the applied strain. The results confirm a significant reduction of the effective mass associated with the lowest, twofold degenerate subband for tensile uniaxial strain.