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Silicon carbide single and multilayer thin films for photovoltaic applications
von Matthias KünleIn this thesis, the deposition and annealing of non-stoichiometric silicon carbide (Si1-xCx) single and Si1-xCx/SiC multilayers has been studied into detail. Furthermore, the integration of Si1-xCx layer stacks into recrystallised wafer equivalents (RexWE) and the application of Si-rich Si1-xCx single and Si1-xCx/SiC multilayers as precursor layers for Si quantum dots in a SiC matrix has been investigated.
An important precondition for the implementation of Si1-xCx single and Si1-xCx/SiC multilayers into photovoltaic devices is the accurate control of the the film thickness and stoichiometry. Amorphous hydrogenated Si1-xCx (a-Si1-xCx: H) thin films were prepared by plasma enhanced chemical vapour deposition (PECVD) using the decomposition of silane (SiH4) and methane (CH4). In the silane-starving low power plasma density regime, homogeneous and nanovoid-free films can be deposited with an accurate control of the film thickness. The composition of the Si1-xCx films can be varied from x = 0.15 to x = 55 solely by changing the SiH4/CH4 gas flow ratio. A higher plasma power density during the deposition favours the decomposition of SiH4 and CH4 in the plasma and increases the C incorporation and the deposition rate. Si-rich a-Si1-xCx: H film consist of Si-C, Si-Si and Si-Hn bonds, whereas C-rich a- Si1-xCx: H film are mostly composed of Si-C, C-C and C-Hn bonds. Due to the variation of the stoichiometry the optical and electronic properties of the films can be varied in a wide range. The refractive index is 2.4 for C-rich films and can be increased up to 3.5 for Si-rich a-Si1-xCx: H films. The optical bandgap shifts due to the increased incorporation of C into the amorphous network of a- Si1-xCx: H films and reaches values from 2.1 eV to 2.6 eV. Moreover, the influence of the deposition temperature on the properties of Si1-xCx films was studied. The standard depositions were done at a substrate temperature of 280°C. An increased substrate temperature during deposition resulted in a reduced growth rate and a reduced C incorporation into the Si1-xCx film. Fourier transformed infrared (FTIR) spectroscopy implied a higher density of the films deposited at higher temperatures. Due to the higher density of the films, the refractive index is also increased.
An important precondition for the implementation of Si1-xCx single and Si1-xCx/SiC multilayers into photovoltaic devices is the accurate control of the the film thickness and stoichiometry. Amorphous hydrogenated Si1-xCx (a-Si1-xCx: H) thin films were prepared by plasma enhanced chemical vapour deposition (PECVD) using the decomposition of silane (SiH4) and methane (CH4). In the silane-starving low power plasma density regime, homogeneous and nanovoid-free films can be deposited with an accurate control of the film thickness. The composition of the Si1-xCx films can be varied from x = 0.15 to x = 55 solely by changing the SiH4/CH4 gas flow ratio. A higher plasma power density during the deposition favours the decomposition of SiH4 and CH4 in the plasma and increases the C incorporation and the deposition rate. Si-rich a-Si1-xCx: H film consist of Si-C, Si-Si and Si-Hn bonds, whereas C-rich a- Si1-xCx: H film are mostly composed of Si-C, C-C and C-Hn bonds. Due to the variation of the stoichiometry the optical and electronic properties of the films can be varied in a wide range. The refractive index is 2.4 for C-rich films and can be increased up to 3.5 for Si-rich a-Si1-xCx: H films. The optical bandgap shifts due to the increased incorporation of C into the amorphous network of a- Si1-xCx: H films and reaches values from 2.1 eV to 2.6 eV. Moreover, the influence of the deposition temperature on the properties of Si1-xCx films was studied. The standard depositions were done at a substrate temperature of 280°C. An increased substrate temperature during deposition resulted in a reduced growth rate and a reduced C incorporation into the Si1-xCx film. Fourier transformed infrared (FTIR) spectroscopy implied a higher density of the films deposited at higher temperatures. Due to the higher density of the films, the refractive index is also increased.