Crystalline, Phononic, and Electronic Properties of Heterostructured Polytypic Ge Nanowires by Raman Spectroscopy

Abstract

Semiconducting nanowires (NWs) offer the unprecedented opportunity to host different crystal phases in a nanostructure, which enables the formation of polytypic heterostructures where the material composition is unchanged. This characteristic boosts the potential of polytypic heterostructured NWs for optoelectronic and phononic applications. In this work, we investigate cubic Ge NWs where small (∼20 nm) hexagonal domains are formed due to a strain-induced phase transformation. By combining a nondestructive optical technique (Raman spectroscopy) with density-functional theory (DFT) calculations, we assess the phonon properties of hexagonal Ge, determine the crystal phase variations along the NW axis, and, quite remarkably, reconstruct the relative orientation of the two polytypes. Moreover, we provide information on the electronic band alignment of the heterostructure at points of the Brillouin zone different from the one (Γ) where the direct band gap recombination in hexagonal Ge takes place. We demonstrate the versatility of Raman spectroscopy and show that it can be used to determine the main crystalline, phononic, and electronic properties of the most challenging type of heterostructure (a polytypic, nanoscale heterostructure with constant material composition). The general procedure that we establish can be applied to several types of heterostructures.

New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe2 and unambiguous determination of few-layer-flakes’ thickness

“…where + ' is the Raman susceptibility tensor calculated ab initio in the reference system of the experiment, while $ " and $ # are the polarization vectors of the incident and scattered light, respectively. This method is deeply explained in references [45] [46]. Once the intensity for each phonon mode has been calculated, Raman spectra are generated by summing up Lorentzian functions, each associated to a calculated mode frequency.…”

Surface chemistry effects on work function, ionization potential and electronic affinity of Si(100), Ge(100) surfaces and SiGe heterostructures

“…6. Results are obtained by aligning the band edges of the X:Si(100) and X:Ge(100) surfaces with respect to the vacuum energy (noticeably a similar approach was adopted by C. Fasolato et al 107 to predict the band alignment at the interface in polytypic Ge NWs of large diameter). Here we compare the band energy line-up calculated for H:SiGe(100) with the ones obtained for X = -I, -Br, -Cl, -F (halogens, top panel of Fig.…”

Hole and Electron Effective Masses in Single InP Nanowires with a Wurtzite-Zincblende Homojunction

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