Dresden 2006 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 50: Poster II

HL 50.9: Poster

Donnerstag, 30. März 2006, 16:30–19:00, P3

Type-I alignment and direct fundamental gap in SiGe based heterostructures — •Michele Virgilio and Giuseppe Grosso — NEST-INFM and Dipartimento di Fisica, Universita’ di Pisa, Largo Pontecorvo 3, I-56127 Pisa, Italy

We study the electronic structure of strained Si1-xGex alloys grown on (001) Si1-yGey cubic substrates. Valence and conduction band offsets at the heterointerfaces and the fundamental gap of the strained alloys are derived for all the (x,y) concentrations, adopting a first neighbors tight binding Hamiltonian description. The localized base includes sp3d5s* orbitals and spin-orbit interaction. Appropriate scaling laws for the hopping parameters are used to describe the geometrical lattice distortion induced by strain. In this way we are able to distinguish in the (x,y) plane a region characterized by robust type I alignment. Information on valence and conduction band alignment as function of alloying and strain together with suitable control of the folding mechanism along the growth direction and of the dependence of the confinement energies from the geometry, are exploited to propose a type-I SiGe quantum well. For this device electronic structure and density of states projected on each orbital and on each layer are studied by means of an iterative manipulation of the Green’s function, overcoming in this way the computational difficulties related to direct diagonalization of the large period structures studied. We can therefore demonstrate that suitable choice of Ge concentrations in the substrate, spacer and active materials allows to obtain structures which are direct gap both in k- and in r space.