Optical properties of silicon germanide strained layer superlattices

Advances in SiGe molecular beam epitaxy (MBE) have allowed the growth of high quality Si{dollar}sb{lcub}rm m{rcub}{dollar}Ge{dollar}sb{lcub}rm n{rcub}{dollar} strained layer superlattices (SLS) despite the 4.2% lattice mismatch between Si and Ge. Si{dollar}sb{lcub}rm m{rcub}{dollar}Ge{dollar}sb{lcub}rm n{rcub}{dollar} SLSs are obtained by growing an alternate sequence of m layers of Si followed by n layers of Ge. In this manner, an "artificial" periodicity is introduced and Brillouin zone folding is expected to occur.; In this thesis, photoluminescence (PL) is used to study the optical properties of Si{dollar}sb{lcub}rm m{rcub}{dollar}Ge{dollar}sb{lcub}rm n{rcub}{dollar} SLSs. Raman scattering (RS), x-ray diffraction (XRD) and cross sectional TEM (XTEM) are employed for the structural characterization of the grown samples. The SLS structures are designed to be strain symmetrized through the use of Si{dollar}sb{lcub}rm 1-x{rcub}{dollar}Ge{dollar}sb{lcub}rm x{rcub}{dollar} buffer layers. This scheme offers more flexibility in the choice of the Si/Ge ratio and the superlattice thickness and periodicity. The buffer layers, designed to be fully relaxed, are not however free of misfit dislocations, which may quench band gap PL. For this reason, a buffer layer is grown thick so that the propagation of misfit dislocations to the superlattice is greatly reduced. Band gap PL may also be quenched by the presence of direct complexes that are inherent to low temperature MBE growth.; PL spectra for different samples are obtained and features below the Si energy band gap are observed.; Rapid thermal annealing (RTA) is used to study the effect of interdiffusion on the SLS luminescence. Raman scattering and x-ray diffraction are employed to monitor interdiffusion. Low temperature annealing is shown (1) not to affect the interface sharpness of the superlattice, (2) to enhance the luminescence of the observed transitions and (3) to shift them slightly to higher energy. Higher temperature annealing, on the other hand, causes (1) considerable interdiffusion and a loss of interface sharpness, (2) a decrease in the luminescence intensity of the transitions and (3) a considerable shift of these transitions to higher energy. The shift to higher energy is due to RTA-induced interdiffusion that makes the quantum wells effectively more parabolic. (Abstract shortened with permission of author.)...