Photoluminescence and Raman scattering in three-dimensional Si/Si1−xGex nanostructures

Abstract

We report detailed Raman and photoluminescence (PL) measurements in Si/Si1−xGex nanostructures grown by molecular-beam epitaxy under conditions of near Stranski–Krastanov (S-K) growth mode. In a series of samples with x controllably increased from 0.098 to 0.53, we observe that an increase in Raman signal related to Ge–Ge vibrations clearly correlates with (i) a redshift in the PL peak position, (ii) an increase in the activation energy of PL thermal quenching, and (iii) an increase in the PL quantum efficiency. The results indicate that in S-K Si/Si1−xGex nanostructures with x>0.5 Ge atoms form nanometer-sized clusters with a nearly pure Ge core and a SiGe shell.

Self‐assembled silicon‐germanium nanostructures for CMOS compatible light emitters

“…Both PL bands are quite broad, most likely due to compositional disorder, which is in agreement with the Raman scattering measurements [9]. There are no characteristic phonons in the Si/SiGe system with an energy of ~100 meV, and it is thus reasonable to assume that the observed PL bands are associated with carrier recombination within two different regions of the 3D SiGe NSs.…”

“…It has been shown that dislocation-free SiGe growth can be achieved using a higher temperature (≥600 o C), and that the non-planar geometry is mainly responsible for the significant increase of the SiGe critical layer thickness [5]. It has also been found that, compared to two-dimemensional (2D) Si/SiGe NSs, the PL and electroluminescence (EL) quantum efficiency in 3D Si/SiGe NSs is higher (up to ~1%), especially for T > 50 K [6][7][8][9]. Despite many successful demonstrations of PL and EL in the spectral range of 1.3-1.6 m, which is important for optical fiber communications, the proposed further development of 3D Si/SiGe based light emitters was discouraged by several studies indicating a type II energy band alignment at Si/SiGe heterointerfaces [10], where the spatial separation of electrons (located in Si) and holes (localized in SiGe) was thought to make carrier radiative recombination very inefficient.…”

Structural and optical properties of axial silicon-germanium nanowire heterojunctions

“…The EDX data indicate that a 2 nm thick Si 0.8 Ge 0.2 layer is formed close to the Si segment of the NW, and this is known to be a stable SiGe alloy composition produced by spontaneous intermixing. 30,31 This is an interesting observation, because the Ge segment of the NW is deposited using a relatively low (350 C) deposition temperature. Most likely, this SiGe transition layer is a result of the presence of residual Si atoms in the eutectic Si-Au alloy after switching to Ge deposition and strain-driven interdiffusion.…”

“…27 This conclusion is supported by the PL2 peak temperature dependence: the PL2 peak disappears at T > 80 K, and this is consistent with a less than 10 meV SiGe composition-fluctuation-related exciton localization energy. 30,31 Considering the PL peak position temperature dependence, the PL peak associated with band-to-band radiative recombination should follow the energy band gap temperature dependence E G (T). In bulk c-Si, the PL peak energy position and line-shape temperature dependencies are explained by taking into account the exciton binding energy (E exc % 10 meV), the phonon-assisted nature of the band-toband recombination involving mostly TO phonons (E ph % 60 meV) and the temperature dependence of population of energy states in the energy bands.…”

X-ray absorption fine structure spectroscopy in nanomaterials

“…necessary to avoid oxidation, is also likely to modify the morphology, structure, electronic and optical properties of Ge QDs [64]. A simultaneous determination of their strain and composition is of interest.…”