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Applications

Applications. Until very recently silicate glasses were the only type of materials commonly used. Advantages over their crystalline counterparts:

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Applications

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  1. Applications

  2. Until very recently silicate glasses were the only type of materials commonly used. Advantages over their crystalline counterparts: Amorphous solids are relatively easy to prepare i.e. large-area, homogeneous amorphous thin film can be prepared. For example a-Si:H for solar cells or thin-film transistors.

  3. Near the glass transition temperature, which is lower than melting point, the materials remain workable so that they can easily be formed into various shapes. Amorphous materials, particularly bulk glasses are often structurally homogeneous and isotropic and their physical properties are also homogeneous and isotropic, unlike crystalline materials.

  4. Various applicationsBrief summary Amorphous semiconductors are promising electronic materials for wide range of applications such as:

  5. Solar cell • Thin film transistors (TFT) • Light sensors • Optical memory devices • Electro photographic application • X-ray image sensors • Eu-doped optical fiber • DVD (digital video/versatile disc) • Hard cover made from ta-C

  6. Various applicationsDetails • Electro photographic application: one of the most common, everyday used application is electro photography or xerography (Greek word, meaning is “dry writing”). The first xerography was made by Carlson and Kornei in 1938(!) in Astoria NY (USA).

  7. The really first experiment was made using sulfur, but later on Se was the basic material. Recently a-Si:H films have been utilized instead. ( I. Shimizu: 1985 J. Non-Cryst. Sol. 77-78, 1363 ).

  8. Solar cells: Potentially the most important application of the amorphous semiconductors a-Si:H is in the direct conversion of sunlight to electric power. • This is a cheaper raw material than crystalline silicon. No structural damage! For example: space shuttle use.

  9. The conversation of solar light to electric power is available renewaable sources of energies. • The basic physical principle involved is the absorption of photon resulting in the creation of electron-hole pairs; the excess electrons in the conduction band, and holes in the valence band. • Internal junction field separates them before recombination.

  10. There are several conditions that a thin film solar cell must satisfy in order to exhibit efficient photovoltaic energy conversion: • The optical absorption coefficient (α) must be large enough • The photogenerated electrons and holes must be collected efficiently by contacting electrodes on the both sides of the active film material

  11. Phase change memory

  12. Base crystalline form amorphous form rapid reversible transition

  13. Bit formation • ~ 1 ns laser heating above melting point, Tm causes amorphous (polycrystalline) nanosize bit. • ~50 ns laser heating above glass transition temperature, but below Tm forms crytalline bit. Rewriteable

  14. Monitoring • Resistivity • Optical reflectivity Phase change materials are the memory materials of the future: 1. Fast (~ 10 ns) 2. Dense (bit diameter < 50 nm) 3. Stable (several years per lost bit) 4. Long-lived (> 1012 cycles per lost bit) 5. Low manufactoring cost 6. Low power consumption

  15. The end

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