Hydrogenated amorphous silicon has been widely studied last years, both from the basic research and industrial points of view, due to the important set of potential applications that this material offers, ranging from Thin Films Transistors (TFTs) to solar cells technologies. In different fabrication steps of a-Si:H based devices, laser sources have been used as appropriate tools for cutting, crystallising, contacting, patterning, etc., and more recent research lines are undertaking the problem of a-Si:H selective laser ablation for different applications.
The controlled ablation of photovoltaic materials with minimum debris and small heat affected zone with low processing costs, is one of the main difficulties for the successful implementation of laser micromachining as competitive technology in this field. This work presents a detailed study of a-Si:H laser ablation in the ns regime. Ablation curves are measured and fluence thresholds are determined. Additionally, and due to the improved performance in optolectronic properties associated to the nanocrystalline silicon (nc-Si:H), some samples of this material have been also studied.
Position detectors are useful for alignment and orientation sensing. Charge-coupled devices (CCDs) are used in small-area systems. Four-quadrant diodes are a low-cost, limited-accuracy alternative. In cases where either large area or reliability under harsh conditions are required, thin-film-silicon sensors may become the only reasonable choice. The paper proposes a simple structure for making such devices, describes the first experiments and discusses the key issues faced, with emphasis on laser scribing.
Laser micromachining of semiconductor and Transparent Conductive Oxides (TCO) materials is very important for the practical applications in photovoltaic industry. In particular, a problem of controlled ablation of those materials with minimum of debris and small heat affected zone is one of the most vital for the successful implementation of laser micromachining.
In particular, selective ablation of thin films for the development of new photovoltaic panels and sensoring devices based on amorphous silicon (a-Si) is an emerging field, in which laser micromachining systems appear as appropriate tools for process development and device fabrication. In particular, a promising application is the development of purely photovoltaic position sensors. Standard p-i-n or Schottky configurations using Transparent Conductive Oxides (TCO), a-Si and metals are especially well suited for these applications, appearing selective laser ablation as an ideal process for controlled material patterning and isolation.
In this work a detailed study of laser ablation of a widely used TCO, Indium-tin-oxide (ITO), and a-Si thin films of different thicknesses is presented, with special emphasis on the morphological analysis of the generated grooves. The profiles of ablated grooves have been studied in order to determine the best
processing conditions, i.e. laser pulse energy and wavelength, and to asses this technology as potentially competitive to standard photolithographic processes.
The encouraging results obtained, with well defined ablation grooves having thicknesses in the order of 10 μm both in ITO and a-Si, open up the possibility of developing a high-performance double Schottky photovoltaic matrix position sensor.