SI1-XGEX SI(001) LAYERS UNDER EXTERNAL UNIAXIAL-STRESS - PHOTOLUMINESCENCE STUDIES/

MBE grown pseudomorphic Si1-xGex/Si(001) quantum wells (QW's) with ger manium contents from 10% to 36% and various thicknesses were studied b y photoluminescence (PL) under external stress applied parallel or per pendicular to the growth direction, Stress perpendicular to the growth direction reduces the symmetry and leads to additional splittings in both barrier and layer material, Bending the whole wafer, we create co mpressive or tensile in-plane strains in the sample. In both cases we could not observe the splittings in the SiGe layers, but the SiGe PL s hifts like the SiGe band edge, as expected from deformation potential theory, Parallel stress conserves the tetragonal symmetry and reduces the strain in the SiGe-layer, and at the same time leads to a splittin g of valence and conduction band states in the Si barrier. For stress values up to 600 MPa we find an upshift of the SiGe FL, whereas the lo west branch of the bound exciton emission of the Si barriers shifts do wn, The observed shift rates depend on both Ge concentration and layer thickness. For thick layers, the shift rates are as expected from def ormation potential theory for the SiGe bandedge. For thin layers signi ficant deviations occur. To interpret these deviations, calculations h ave been carried out which take into account quantization energies in the QW's, stress dependent exciton binding energies, band bending effe cts, and stress dependence of band offsets.