Final Report Summary - NOVOSIP (Nano-Voids in Strained Silicon for Plasmonics)
The project No 298932 (NoVoSiP) aims at exploring the use of nano-voids and nano-dots prepared as plasmonic structures to enhance the efficiency of Si single-crystalline photovoltaic devices. The main idea behind the production of nanovoids and nano-dots is based on the ability of compressively strained thin SiGe alloy layers, incorporated in a Si matrix during epitaxial growth, to collect vacancies and small-sized molecules followed by thermally activated self-assembling of the nano-voids. The voids are additionally used as templates for self-assembling of metallic nano-shells, nano-dots and carbon nano-flakes. Void containing Si/SiGe strained structures will be further investigated in a photovoltaic device configuration to utilise both near-field and far field effects. The voided structures offer unique possibilities for fundamental investigations.
By combing results from transmission-electron microscopy, Rutherford backscattering spectrometry, secondary-ion mass spectroscopy, optical and photocurrent measurements, the following main results have been obtained after the first 2-year period of the project:
- Self-assembling of spherically shaped voids in nanometer sized, strained Sn precipitates takes place during high-temperature ion irradiation of Si/SiSn/Si layered structure. This is accompanied by a - to - phase transformation in the Sn precipitates. The structures are promising for opto-electronic applications (light-emitting devices, photovoltaic devices).
- Formation of carbon nano-flakes in strained multilayered Si/SiGe/Si structures after combined MBE growth, carbon ion implantation, and thermal treatment is found after anomalous carbon redistribution in the strained SiGe/Si layers. Raman spectra reveal peaks at 1600 and 2700 cm-1 which might be associated with carbon-related multi-layered graphen-like phases.
- Carbon related suppression of tin precipitation and elimination of dislocations in supersaturated molecular-beam epitaxial grown SiSn alloy layers is established in the SiSn layers after carbon implantation and high temperature thermal treatment. Strain-enhanced separation of point defects and formation of dopant-defect complexes are suggested to be responsible for the effects. Possible implementation for carbon assisted segregation-free high temperature growth of metastable heteroepitaxial SiSn/Si and GeSn/Si structures is argued. Such structures are promising for optoelectronic applications.
- A new concept for self-assembling of metallic nano-shells and nano-particles in the strained Si/SiGe heterostructures is proposed and developed. Optical measurements of such layers show increased absorption in the infrared spectral range of 800 – 1800 nm. The metallic nano-shells will be further investigated in solar cell structures for demonstration of plasmonic effects.
- A plasmonic-related gas sensing effect is demonstrated in SnO2/Ag nano-composite layers with Kirkendall voids. The nano-composite layers are produced by magnetron sputtering of Sn1-xAgx alloy on fused silica (FS) followed by oxidation at high temperature. Silver nano- particles are then segregated into Kirkendall voids inthe SnO2 layer. The spectral shift of the plasmon-resonance peak depends on gas atmosphere and temperature. The concept of plasmonic based SnO2 sensors has been discussed.
The results of investigations carried out in the first period of the project will be used for preparation of plasmonic structures to enhance the efficiency of Si-based photovoltaic devices, solid-state gas sensors, and strained Si/SiGe multilayered plasmonic in opto-electronic devices (light emitting and photodetecting) structures.
The results of the investigations are being collected and presented at the Project website: http://phys.au.dk/forskning/forskningsomraader/semiconductor/projects/light-and-nano-particles/nanovoids/. The website is under construction and will be totally available after the second period of the Project.
By combing results from transmission-electron microscopy, Rutherford backscattering spectrometry, secondary-ion mass spectroscopy, optical and photocurrent measurements, the following main results have been obtained after the first 2-year period of the project:
- Self-assembling of spherically shaped voids in nanometer sized, strained Sn precipitates takes place during high-temperature ion irradiation of Si/SiSn/Si layered structure. This is accompanied by a - to - phase transformation in the Sn precipitates. The structures are promising for opto-electronic applications (light-emitting devices, photovoltaic devices).
- Formation of carbon nano-flakes in strained multilayered Si/SiGe/Si structures after combined MBE growth, carbon ion implantation, and thermal treatment is found after anomalous carbon redistribution in the strained SiGe/Si layers. Raman spectra reveal peaks at 1600 and 2700 cm-1 which might be associated with carbon-related multi-layered graphen-like phases.
- Carbon related suppression of tin precipitation and elimination of dislocations in supersaturated molecular-beam epitaxial grown SiSn alloy layers is established in the SiSn layers after carbon implantation and high temperature thermal treatment. Strain-enhanced separation of point defects and formation of dopant-defect complexes are suggested to be responsible for the effects. Possible implementation for carbon assisted segregation-free high temperature growth of metastable heteroepitaxial SiSn/Si and GeSn/Si structures is argued. Such structures are promising for optoelectronic applications.
- A new concept for self-assembling of metallic nano-shells and nano-particles in the strained Si/SiGe heterostructures is proposed and developed. Optical measurements of such layers show increased absorption in the infrared spectral range of 800 – 1800 nm. The metallic nano-shells will be further investigated in solar cell structures for demonstration of plasmonic effects.
- A plasmonic-related gas sensing effect is demonstrated in SnO2/Ag nano-composite layers with Kirkendall voids. The nano-composite layers are produced by magnetron sputtering of Sn1-xAgx alloy on fused silica (FS) followed by oxidation at high temperature. Silver nano- particles are then segregated into Kirkendall voids inthe SnO2 layer. The spectral shift of the plasmon-resonance peak depends on gas atmosphere and temperature. The concept of plasmonic based SnO2 sensors has been discussed.
The results of investigations carried out in the first period of the project will be used for preparation of plasmonic structures to enhance the efficiency of Si-based photovoltaic devices, solid-state gas sensors, and strained Si/SiGe multilayered plasmonic in opto-electronic devices (light emitting and photodetecting) structures.
The results of the investigations are being collected and presented at the Project website: http://phys.au.dk/forskning/forskningsomraader/semiconductor/projects/light-and-nano-particles/nanovoids/. The website is under construction and will be totally available after the second period of the Project.
