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Large area Germanium Tin nanometer optical film coatings on highly flexible aluminum substrates

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ABSTRACT

Germanium Tin (GeSn) films have drawn great interest for their visible and near-infrared optoelectronics properties. Here, we demonstrate large area Germanium Tin nanometer thin films grown on highly flexible aluminum foil substrates using low-temperature molecular beam epitaxy (MBE). Ultra-thin (10–180 nm) GeSn film-coated aluminum foils display a wide color spectra with an absorption wavelength ranging from 400–1800 nm due to its strong optical interference effect. The light absorption ratio for nanometer GeSn/Al foil heterostructures can be enhanced up to 85%. Moreover, the structure exhibits excellent mechanical flexibility and can be cut or bent into many shapes, which facilitates a wide range of flexible photonics. Micro-Raman studies reveal a large tensile strain change with GeSn thickness, which arises from lattice deformations. In particular, nano-sized Sn-enriched GeSn dots appeared in the GeSn coatings that had a thickness greater than 50 nm, which induced an additional light absorption depression around 13.89 μm wavelength. These findings are promising for practical flexible photovoltaic and photodetector applications ranging from the visible to near-infrared wavelengths.

No MeSH data available.


(a) XRD patterns of GeSn nanometer coating on Al foil. (b) Enlarged XRD patterns with 2θ ranging from 40° to 50°.
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f3: (a) XRD patterns of GeSn nanometer coating on Al foil. (b) Enlarged XRD patterns with 2θ ranging from 40° to 50°.

Mentions: In order to describe the lattice deformation, we study the microstructure of the GeSn nanometer coatings on Al foil using XRD. The XRD patterns are shown in Fig. 3(a), most visible are the Al peaks from the substrate. With GeSn thickness t increasing up to 50 nm, GeSn (111) phase and GeSn (220) phase gradually appear. β-Sn (200) and (101) phases also appear corresponding to samples of high relative thickness. Raman analysis proved that the lattice strain changes considerably for different thicknesses of GeSn films. Here, as shown in Fig. 3(b), a large GeSn (220) peak shift is observed in the enlarged XRD patterns. The higher diffraction angle indicates a change to smaller lattice constants, which means the lattice constant of GeSn decreases for t larger than 50 nm. It has been shown that the epitaxial breakdown would change the surface morphology from a 2D growth mode to a 3D growth mode with large islands26. It is conjectured that Sn-rich precipitates will form on the GeSn thin films with t larger than 50 nm. The composition of the GeSn film changes with epitaxial breakdown, which can explain the decrease of GeSn lattice constant and the concomitant appearance of the β-Sn phase.


Large area Germanium Tin nanometer optical film coatings on highly flexible aluminum substrates
(a) XRD patterns of GeSn nanometer coating on Al foil. (b) Enlarged XRD patterns with 2θ ranging from 40° to 50°.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036029&req=5

f3: (a) XRD patterns of GeSn nanometer coating on Al foil. (b) Enlarged XRD patterns with 2θ ranging from 40° to 50°.
Mentions: In order to describe the lattice deformation, we study the microstructure of the GeSn nanometer coatings on Al foil using XRD. The XRD patterns are shown in Fig. 3(a), most visible are the Al peaks from the substrate. With GeSn thickness t increasing up to 50 nm, GeSn (111) phase and GeSn (220) phase gradually appear. β-Sn (200) and (101) phases also appear corresponding to samples of high relative thickness. Raman analysis proved that the lattice strain changes considerably for different thicknesses of GeSn films. Here, as shown in Fig. 3(b), a large GeSn (220) peak shift is observed in the enlarged XRD patterns. The higher diffraction angle indicates a change to smaller lattice constants, which means the lattice constant of GeSn decreases for t larger than 50 nm. It has been shown that the epitaxial breakdown would change the surface morphology from a 2D growth mode to a 3D growth mode with large islands26. It is conjectured that Sn-rich precipitates will form on the GeSn thin films with t larger than 50 nm. The composition of the GeSn film changes with epitaxial breakdown, which can explain the decrease of GeSn lattice constant and the concomitant appearance of the β-Sn phase.

View Article: PubMed Central - PubMed

ABSTRACT

Germanium Tin (GeSn) films have drawn great interest for their visible and near-infrared optoelectronics properties. Here, we demonstrate large area Germanium Tin nanometer thin films grown on highly flexible aluminum foil substrates using low-temperature molecular beam epitaxy (MBE). Ultra-thin (10–180 nm) GeSn film-coated aluminum foils display a wide color spectra with an absorption wavelength ranging from 400–1800 nm due to its strong optical interference effect. The light absorption ratio for nanometer GeSn/Al foil heterostructures can be enhanced up to 85%. Moreover, the structure exhibits excellent mechanical flexibility and can be cut or bent into many shapes, which facilitates a wide range of flexible photonics. Micro-Raman studies reveal a large tensile strain change with GeSn thickness, which arises from lattice deformations. In particular, nano-sized Sn-enriched GeSn dots appeared in the GeSn coatings that had a thickness greater than 50 nm, which induced an additional light absorption depression around 13.89 μm wavelength. These findings are promising for practical flexible photovoltaic and photodetector applications ranging from the visible to near-infrared wavelengths.

No MeSH data available.