ALD of phase controlled tin monosulfide thin...
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a) a) Acknowledgement References ALD of phase controlled tin monosulfide thin films Oleksandr Bilousov 1 , Yi Ren 1 , Tobias Törndahl 1 , Olivier Donzel-Gargand 1 , Tove Ericson 1 , Charlotte Platzer-Björkman 1 , Marika Edoff 1 and Carl Hägglund 1 1 Ångström Solar Center, Solid State Electronics, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden ([email protected] and [email protected]) Tin monosulfide (SnS) is a promising semiconductor material for low-cost conversion of solar energy, playing the role of absorber layer in photovoltaic devices. SnS is, due to its high optical damping, also an excellent semiconductor candidate for the realization of ultrathin (nanoscale thickness) plasmonic solar cells [1]. Here, we present an important step to further control and understand SnS film properties produced using low temperature ALD with Sn(acac) 2 and H 2 S as precursors. We show that the SnS film properties vary over a rather wide range depending on substrate temperature and reaction conditions, and that this is connected to the growth of cubic (π-SnS) and orthorhombic SnS phases. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry [2]. Optical properties Financial support from The Swedish Research Council (621- 2014-5599) is gratefully acknowledged. Introduction Results Conclusions 1. C. Hägglund, G. Zeltzer, R. Ruiz, A. Wangperawong, K. E. Roelofs, S. F. Bent, ACS Photonics 3 (3) (2016) 456–463. 2. O. V. Bilousov, Y. Ren, T. Törndahl, O. Donzel- Gargand , T. Ericson, C. Platzer-Björkman, M. Edoff, and C. Hägglund, ACS Chemistry of Materials 29 (7) (2017) 2969–2978. • Direct forbidden optical bandgap of 1.64 eV for the cubic SnS phase based on linear extrapolation in a Tauc plot. • An exponential, Urbach type dependence for orthorhombic SnS over at least two decades, with a tail width of 0.3 to 0.4 eV. • The origin of the tail is ascribed to the nanoscale structural disorder of the blade-like morphology, to sulfur vacancies of the orthorhombic SnS, or to their combination Cubic SnS Orthorhombic SnS Cubic SnS Spatial distribution of the SnS phases • As the sampling depth increases along with the angle of incidence up to 0.5°, the relative intensities of the cubic SnS (222) and (400) peaks rise for a sample with intermediate (1.6 s) H 2 S dose. • This suggests a gradient with a more cubic phase near the bottom of the film and a more orthorhombic phase towards the SnS surface. • The bottom of the layer is compact and void free. The top layer on the other hand exhibits high roughness with protruding blade-like grains. • The grain size of the SnS increases with increasing growth temperature. • At the highest temperature, the surface is dominated by blade- like grains with a resulting high roughness. 1000 cycles Crystal structure of cubic SnS versus thickness • Films with mainly cubic phase SnS is formed at 120 °C using a long (5 s) H 2 S pulse length • Grains are columnar and extend over the entire film thickness (42-43 nm for 1000 cycles) with more or less vertical grain boundaries Effect of H 2 S dose and temperature on SnS growth • The crystal structure and morphology undergoes a notable evolution as the H 2 S dose varies. Cubic SnS forms at high H 2 S dose. An ALD process for orthorhombic and cubic phases of SnS thin film deposition, using sequential exposures of Sn(acac) 2 and H 2 S precursors. For the first time SnS of cubic phase is obtained by ALD at saturated conditions. A direct forbidden band gap of 1.64 eV is observed. Uniform SnS thin films over large area are achieved with controlled thickness and crystallographic phase on Si and glass substrates.
Transcript of ALD of phase controlled tin monosulfide thin...
a)a)
AcknowledgementReferences
ALD of phase controlled tin monosulfide thin filmsOleksandr Bilousov1, Yi Ren1, Tobias Törndahl1, Olivier Donzel-Gargand1, Tove Ericson1,
Charlotte Platzer-Björkman1, Marika Edoff1 and Carl Hägglund1
1 Ångström Solar Center, Solid State Electronics, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden ([email protected] and [email protected])
Tin monosulfide (SnS) is a promising semiconductor material for low-cost conversion of solar energy, playing the roleof absorber layer in photovoltaic devices. SnS is, due to its high optical damping, also an excellent semiconductorcandidate for the realization of ultrathin (nanoscale thickness) plasmonic solar cells [1].
Here, we present an important step to further control and understand SnS film properties produced using lowtemperature ALD with Sn(acac)2 and H2S as precursors. We show that the SnS film properties vary over a rather widerange depending on substrate temperature and reaction conditions, and that this is connected to the growth of cubic(π-SnS) and orthorhombic SnS phases. The optical properties of the two polymorphs differ significantly, asdemonstrated by spectroscopic ellipsometry [2].
Optical properties
Financial supportfrom The Swedish Research Council (621-2014-5599) is gratefully acknowledged.
Introduction
Results
Conclusions
1. C. Hägglund, G. Zeltzer, R. Ruiz, A. Wangperawong, K. E. Roelofs, S. F. Bent, ACS Photonics 3 (3) (2016) 456–463.
2. O. V. Bilousov, Y. Ren, T. Törndahl, O. Donzel-Gargand , T. Ericson, C. Platzer-Björkman, M. Edoff, and C. Hägglund, ACS Chemistry ofMaterials 29 (7) (2017) 2969–2978.
• Direct forbidden optical bandgap of 1.64 eV for the cubic SnS phase based on linearextrapolation in a Tauc plot.
• An exponential, Urbach type dependence for orthorhombic SnS over at least twodecades, with a tail width of 0.3 to 0.4 eV.
• The origin of the tail is ascribed to the nanoscale structural disorder of the blade-likemorphology, to sulfur vacancies of the orthorhombic SnS, or to their combination
Cubic SnS
Orthorhombic SnS
Cubic SnS
Spatial distribution of the SnS phases
• As the sampling depth increases along with the angle of incidence up to 0.5°, the relative intensities of the cubic SnS (222) and (400) peaks rise for a sample with intermediate (1.6 s) H2S dose.
• This suggests a gradient with a more cubic phase near the bottom of the film and a more orthorhombic phase towards the SnS surface.
• The bottom of the layer is compact and void free. The top layer on the other hand exhibits high roughness with protruding blade-like grains.
• The grain size of the SnSincreases with increasing growth temperature.
• At the highest temperature, the surface is dominated by blade-like grains with a resulting high roughness.
1000 cycles
Crystal structure of cubic SnS versus thickness
• Films with mainly cubic phase SnS is formed at 120 °C using a long (5 s) H2S pulse length
• Grains are columnar and extend over the entire film thickness (42-43 nm for 1000 cycles) with more or less vertical grain boundaries
Effect of H2S dose and temperature on SnS growth
• The crystal structure and morphology undergoes a notable evolution as the H2S dose varies. Cubic SnS forms at high H2S dose.
An ALD process for orthorhombic and cubic phases of SnS thin film deposition, usingsequential exposures of Sn(acac)2 and H2S precursors.
For the first time SnS of cubic phase is obtained by ALD at saturated conditions. A directforbidden band gap of 1.64 eV is observed.
Uniform SnS thin films over large area are achieved with controlled thickness andcrystallographic phase on Si and glass substrates.
