Influence of the dopant on the contact formation to p+-type silicon

AbstractIn this contribution we investigate the influence of the doping element on the contact formation to p+-type Si. Contacting B doped layers with Ag thick film paste leads to very few Ag crystallites at the contact interface and results in poor contact resistances [1–3]. Using Ag/Al thick film paste for contact formation, the contact is not only formed by Ag crystallites, but by diversely shaped Ag/Al contact spots and the contact resistance is reduced by more than one order of magnitude [2]. Al melting at the Si wafer surface forms Al doped rectangles on the Si wafer where the growth of Ag/Al/Pb spikes is enhanced.When contacting Al doped layers with Ag thick film paste a larger number of Ag crystallites is observed than for B doped layers. If the contact is formed with Ag/Al paste the number of Al-rich rectangles is enhanced and we detect higher doped areas under the contact spots. The contacts detected have an ellipsoidal, pyramidal or “L-formed” shape. We conclude that not only the acceptor impurity concentration under the contact area is crucial for the contact formation, but also the properties of the specific acceptor present

Annealing and oxygen role in the structural, optical and electrical properties of nc-SiOxNy

Research in the renewable energy field is mandatory to provide alternatives to fossil fuels in energy production and photovoltaics is very promising as solar energy is widely distributed. Moreover, the related technology is nowadays easily available, it can be integrated with buildings and presents limited environmental issues. Silicon Oxi-Nitride (SiOxNy) thin films have been characterized in view of the application in thin-film solar cells as well as in wafer based silicon solar cells, like Silicon HeteroJunction (SHJ) solar cells. Material properties like optical and electronic properties of the film, composition and structure of the nanocrystals have not been studied yet. In addition, the role of deposition conditions and precursor gas concentrations on these properties is also not clear. The results presented in the contribution aim to clarify several aspects concerning nc-SiOxNy film properties

Annealing effects on SiOxNy thin films: Optical and morphological properties

The annealing effect on the properties of silicon oxynitride (SiOxNy) thin films has been investigated. The present contribution aims to study the structural and optical properties of SiOxNy thin films deposited by plasma enhanced chemical vapor deposition in view of their application in the field of photovoltaics. Evolution of the surface morphology and increase of the optical band gap with the thermal treatment have been determined and discussed in view of the application of the film as an emitter layer in heterojunction solar cells

Dopant mapping in highly p-doped silicon by micro-Raman spectroscopy at various injection levels

Micro-Raman spectroscopy has been used to investigate the acceptor distribution in highly p-doped silicon. As an example, the dopant distribution in crystalline thin-film layers, as developed for solar cells, was mapped. The method is based on the analysis of the Fano-type Raman peak shape which is caused by free charge carriers. For calibration of the Raman acceptor measurements (excitation at a wavelength of 532 nm), we used mono-crystalline reference samples whose acceptor concentration was determined by electrochemical capacitance voltage. We find a significant influence of light induced free charge carriers on the peak shape which results from typical Raman excitation. Thus, the selection of a suitable intensity is important to avoid a too low signal-to-noise ratio on the one hand and systematic errors due to light induced carriers on the other hand. Different evaluation methods, i.e., peak asymmetry versus peak width analysis, are compared in respect to interference caused by random noise of the spectra or else by internal stress in the sample. While the width analysis method is more robust to a low signal-to-noise ratio, the symmetry analysis is more reliable in case of high intrinsic stress

Microstructural and electrical properties of silicon-oxy-nitride layers for photovoltaic applications

Silicon heterojunction solar cells (SHJ) attracted a lot of attention in recent years due to their high efficiency potential and low temperature production process. In the present study nano-crystalline Silicon Oxy-Nitrides layers (nc-SiOxNy) are studied in view of their application in SHJ cells since they suffer less parasitic absorption. SiOxNy films deposited by Plasma Enhanced Chemical Vapour Deposition with different parameters were subsequently annealed in order to obtain the formation of nanocrystals. Structural and compositional analyses were performed by Raman and Fourier-Transform Infra-Red (FTIR) spectroscopy and optical characterization. IV measurements were carried out in order to investigate the electrical properties of the layers. Microscopical analyses were performed with Scanning Electron and Atomic Force Microscope (AFM). Samples show high conductivity ranging from 1-40 S/cm demonstrating that the dopants become electrically active and that the layers become nanocrystalline. Through AFM phase contrast analysis we found differences in tip-sample energy dissipation that can be due to variations in the composition and/or crystalline/amorphous phase. Raman spectroscopy has allowed us to detect the evolution of the crystallinity with deposition conditions and annealing time. FTIR shows peak shifts with deposition and annealing parameters. The combination of macroscopical and microscopical techniques gives a fundamental insight on the properties of the material

Annealing effects on SiOxNy thin films: Optical and morphological properties

The annealing effect on the properties of silicon oxynitride (SiOxNy) thin films has been investigated. The present contribution aims to study the structural and optical properties of SiOxNy thin films deposited by plasma enhanced chemical vapor deposition in view of their application in the field of photovoltaics. Evolution of the surface morphology and increase of the optical band gap with the thermal treatment have been determined and discussed in view of the application of the film as an emitter layer in heterojunction solar cells

Light Induced Curing (LIC) of Passivation Layers Deposited on Native Silicon Oxide

AbstractThis work presents a novel insight to the aspects of silicon surface passivation and the influence of thin intermediate layers generated by chemically grown silicon oxides. Strong light induced effects on passivation properties are investigated. After exposure to light (0.25 suns) for about 60 s, samples based on a PECVD layer system consisting of SiNx and SiO2 deposited on crystalline silicon with native silicon oxides show an improvement of more than 100% in minority carrier lifetime. These improvements are stable over months and lead to effective surface recombination velocities as low as 10cm/s on chemically polished p-type FZ wafers. With the use of different light sources, corona charging and annealing experiments the effect is investigated in detail. Finally, the effect is proposed to be a photo induced curing process of defects in the Si/SiO2 interface with the incorporation of hydrogen