Preface: Advanced Silicon Materials Research for Electronic and Photovoltaic Applications

Since the end of our 2010 symposium a significant evolution of the optoelectronic and photovoltaic market took place, leaving, however, silicon and silicon–germanium alloys to remain the materials of choice for a number of mature and advanced applications. The production capacity of Siemens‐type polycrystalline silicon plants, which amounted at 233.000 MT in 2010, continued to increase in 2011, although at a growth rate lower than in the past years. Today, May 2012, there is a substantial unbalance between the silicon production capacity and the requests of a stagnant market, with silicon selling costs dropping close to 25 $/kg. More than 80% of the polycrystalline silicon production was and is used in the photovoltaic sector, which experienced, also, a revolutionary transformation, with a number of producers being capable to bring to the market both high efficiency cells, approaching the 25% efficiency with n‐type substrates and low cost modules, with a market cost well below the 1 €/Wp. With the selling costs of polycrystalline silicon close to the production cost, the question which remains open is whether it will continue to be the only silicon supply for photovoltaic applications or are low cost alternatives to the Siemens process still industrially interesting in terms of quality, cost and energy consumption. But this question has not yet obtained a satisfactory answer, albeit deeply debated also in our symposium. The benefits in terms of efficiency and cost of single crystal, n‐type single crystal substrates caused a sudden drop of interest for multicrystalline substrates. Today, most of the multicrystalline silicon producers are looking to the monocast process, in view of its potential to grow quasi‐single crystal ingots, leading to a significant increase of the average efficiency. The actual merits and challenges of this technology are still under discussion, as only a fraction of the ingot is fully single crystalline, as shown in our symposium as well. Also, thin silicon films, which seemed to be the perfect PV solution when the silicon shortage was becoming acute in 2006, experienced in these last two years a significant drop of interest, with relevant consequences both at the research and production level. Oerlikon sold its solar division to Tokyo Electron (TE) in 2012 and Applied Materials, the major equipment supplier pulled out of the turnkey market already in 2010. As polysilicon prices declined and capacity expansions passed the tens of gigawatt scale, c‐Si technologies became, in fact, highly competitive again. This increasing interest to silicon was and is not confined to photovoltaics. The already existing and still developing knowledge concerning the physics of defects and impurities in silicon represents a possibility to understand the role of defects in low‐dimensional structures, like nanotubes and nanowires. This has also increased the demand for further development of measurement and detection techniques on the nano‐scale. Innovation from materials research is one of the driving forces in future micro‐ and nano‐technologies. The silicon manufacturing infrastructure enables innovation by heterogeneous integration of alternative materials like SiGe or GeSn. Single crystal silicon found recently a new important application window, with IMEC's demonstration that 300 mm diameter Cz wafers could be used as substrates for GaN layers alternatively to sapphire substrates. This application could lead to a revolutionary change of the lighting industry based on nitride LEDs as well as of that of the thin film compound semiconductor solar cells, in view of the fact that In–Ga nitride alloys cover the full solar spectrum. Next generation silicon technologies with ongoing scaled‐down feature size of transistors are asking for improved large area silicon materials (diameter ≥300 mm). Improved silicon crystal pulling processes with reduced density of crystal defects, defect engineered silicon wafers, and the improvement of material features by co‐doping with light elements are the main path to meet the requirements of technologies beyond 90 nm to the silicon substrate material. Thermal processing on the millisecond scale becomes more and more important, e.g. for shallow junctions. Silicon or silicon–germanium on insulator are innovative silicon‐based substrates which allow further improvements of electrical device characteristics. Strain engineered silicon has already proven its capabilities to compensate problems of carrier mobility caused by high‐ k dielectrics and transistor scaling. It is still important to understand the impact of axially different stress and strain components on the device characteristics and carrier mobility. Defect engineered solutions for strained layer adjustment are crucial for the increase of carrier mobility in the strained silicon channels. Although silicon nanowires and nanodots are not yet materials of direct industrial applications, they represent the challenge for many future applications in a variety of fields. Impressive knowledge achievements were obtained in the field of silicon nanodots, whose potentialities in advanced microelectronics and photovoltaics are already well recognized and we learned, as well, to grow silicon nanowires with different technologies and to branch them in the 3D space. The consciousness of a constantly growing interest of new silicon applications, the presence of more than 250, highly ranking scientists from academia and industry, coming from Europe, Africa, Asia, America and Australia, and the exciting and inspiring atmosphere of the various sessions was the main reason of the success of our third Symposium on Advanced Materials Research for Electronic and Photovoltaic Applications (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)