Growth and Characterization of Ultrathin SimGen Strained Layer Superlattices

Abstract

Growth of Ultrrathin SimGen (m monolayers (ML) Si, n ML Ge) strained layer superlattices (SLS) by molecular beam epitaxy (MBE) is reported. Diode structures (doping sequence p+ −n−n+ on n+ −substrate and n+ −n−p+ on p+ −substrate) were grown for optical device applications with strain symmetrization of the SLS by a thin homogeneous buffer layer serving as a virtual substrate. The concept of zone folding is described and the transition matrix elements of the folded bandstructure as a function of period length are calculated. The concept of a virtual substrate consisting of the actual Si-substrate and a thin buffer layer is explained. The strain adjustment of the SLS by choice of the buffer layer composition and the strain symmmetrization is outlined. Different structural (TEM-and X-ray analysis, Rutherford Back Scattering) and optical (Raman, Photoluminescence, modulation spectroscopy) characterization methods of the SLS are discussed. A Raman spectrum of a Si6Ge4 SLS is shown together with an Si0.6Ge0.4 alloy sample, the occuring peaks are discussed.