Thin amorphous silicon

W. Moritz, T. Yoshinobu, F. Finger, S. Krause, M. Martin-Fernandez and M.J. Schoning, High resolution LAPS using amorphous silicon as the semiconductor material, Sens. Actuators B Chem., 103 (2004) 436—441. J.C. van den Heuvel, R.C. van Oort and M.J. Geerts, Diffusion length measurements of thin amorphous silicon layers, Solid State Commun., 69(8) (1989) 807-810. 

As already mentioned in Sects. 6.3.1.2 and 8.2.3, ZnO can be used as an intermediate reflector in a-Si H/ j,c-Si H tandem solar cells between top and bottom cell to increase the current in the thin amorphous silicon top cell [14,15]. As a result, the thickness of the a-Si H top cell can be reduced to improve the stability of the cell upon light induced degradation. Recent progress has even lead to improved light utilization and higher short circuit current density by an optimized intermediate reflector [16]. However, this intermediate reflector might consist of another material than ZnO. 

For the production of thin amorphous silicon layers (e.g., for solar photovoltaic energy converters) often the condensation of gaseous silane (SiH ) or Si2Hg, which is formed in a gas discharge, is utilized. During the formation of Si(H) layers the radical SiH2 plays an important role, which... 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

Fig. 4. Some electronic device applications using amorphous silicon (a) solar cell, (b) thin-fiLm transistor, (c) image sensor, and (d) nuclear particle detector.

Figures High mass resoiution mass spectrum obtained from a phosphorus-doped amorphous silicon hydride thin film using a magnetic sector ion microanalyzer. The peak is well separated from the hydride iirterferences.

Textured Tin Oxide Films Produced by Atmospheric Pressure Chemical Vapor Deposition from Tetramethyltin and Their Usefulness in Producing Light Trapping in Thin-Film Amorphous Silicon Solar Energy Mater., 18 263-281 (1989)... 

The thickness of a photovoltaic cell is chosen on the basis of its ability to absorb sunlight, which in turn depends on the bandgap and absorption coefficient of the semiconductor. For instance, 5 nm of crystalline silicon are required to absorb the same amount of sunlight as 0.1 nm of amorphous silicon and 0.01 nm of copper-indium diselenide. Only MBE and MOCVD are capable of producing such extremely thin films.i l... 

Amorphous Silicon (a-Si). Amorphous silicon is considered a promising new material.As mentioned above, only a very thin coating is necessary, since the amorphous structure is much better at absorbing sunlight than is the crystalline material. The most common process to produce a-Si is the decomposition of silane by plasma CVD (see Ch. 8). Thicknesses of a few micrometers can be deposited and,... 

A thin film of tin oxide with a rough texture, produced by MOCVD from tetramethyl tin, (CH3)4Sn, deposited on an amorphous silicon cell provides a light-trapping surface, which enhances the efficiency of the device. 

We have already mentioned amorphous silicon solar cells. New processes have been developed to manufacture solar cells based upon deposition of very thin films of photosensitive materials. Such processes have a distinct cost advantage since once the films are deposited, little further processing is needed to form the final solar cell module. 

As described earlier, the covalently bonded hydrogen, by passivating dangling bond defects and removing strained weak Si—Si bonds from the network, dramatically improves the semiconducting quality of amorphous silicon. Hence without the presence of hydrogen, effective amorphous semiconductor devices such as solar cells or thin film transistors would not be possible. Unfortunately, low defect density, high electronic quality... 

Schropp, R. E. I. Carius, R. Beaucarne, G. 2007. Amorphous silicon, microcrystalline and thin-film polycrystalline silicon solar cells. MRS Bull. 32 219-223. 

Kuo, Y. (Editor). 2004. Thin-Film Transistors Materials and Processes, Amorphous Silicon Thin-Film Transistors, Polycrystalline Silicon Thin Transistors. Kluwer, New York. 

For example, the thin-film amorphous silicon manufacturing technology in operation at Universal Solar Ovonic (Auburn Hills, MI Accessed http //www.ovonic. com/). 

Hong, C. Wagner, S. 2000. Inkjet printed copper source/drain metallization for amorphous silicon thin-film transistors. IEEE Electron Dev. Lett. 21 384-386. 

B. Schroder, Thin-film technology based on hydrogenated amorphous-silicon, Mater. Sci. Eng., A, 139 319-333, 1991. 

F.R. Zhu, T. Fuyuki, H. Matsunami, and J. Singh, Assessment of combined TCO/metal rare contact for thin film amorphous silicon solar cells, Sol. Energy Mater. Sol. Cells, 39 1-9, 1995. 

MJ Powell, C van Berkel, and JR Hughes, Time and temperature dependence of instability mechanisms in amorphous silicon thin-film transistors, Appl. Phys. Lett., 54 1323-1325, 1989. 

Amorphous Silicon Thin-Film Transistor Active-Matrix Organic Light-Emitting Displays... 

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