Silicon grain boundaries

Good-quality multicrystalline silicon (mc-Si) has been used as a model to develop techniques for depositing silicon on silicon. Grain boundaries... 

Furthermore, even though a consistent quality of beryllium is now produced, the chemical composition falls far short of the standards found for instance in aluminium generally, the main impurities consist of about 1% of beryllia at grain boundaries, about 0-15% of iron and 0-05-01% of other elements such as silicon, aluminium and carbon. 

Seager, C.H., and Ginley, D.S., (1982). Fundamental Studies of Grain Boundary Passivation in Polycrystalline Silicon with Application to Improved Photovoltaic Devices, Sandia Report, SAND82-1701, p. 19-21. 

A schematic view of the cold cathode fabrication process is shown in Fig. 10.18. The cold cathode is fabricated by low pressure chemical vapor deposition (LPCVD) of 1.5 pm of non-doped polysilicon on a silicon wafer or a metallized glass substrate. The topmost micrometer of polysilicon is then anodized (10 mA cnT2, 30 s) in ethanoic HF under illumination. This results in a porous layer with inclusions of larger silicon crystallites, due to faster pore formation along grain boundaries. After anodization the porous layer is oxidized (700 °C, 60 min) and a semi-transparent (10 nm) gold film is deposited as a top electrode. 

H. Ichinose and Y. Ishida. In situ observation of grain boundary migration of silicon E3 boundary and its structural transformation at 1000 K. J. Phys. Colloq. (Paris), 51(suppl. no. 1) C1 185—190, 1990. 

Without zinc, silicon diffusion to the surface is slow under MCS conditions. Furthermore, when only tin is used as a promoter, no Cu is observed at the surface. Table 3 shows the elemental concentration under various conditions. Under MCS reaction conditions, when zinc was present silicon was not depleted from the subsurface, and when zinc was absent the subsurface was depleted in silicon. Zinc causes the rate of silicon diffusion and copper dispersion to increase. Zinc accumulates at grain boundaries and lowers the free energy of CU3SL Tin and zinc appear to work synergistically but tin does not enhance silicon diffusion on its own. Tin does appear to lower the surface energy of silicon/copper. 

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