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					Applications
  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.
 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.
     Various applications
             Brief summary



 Amorphous semiconductors are
promising electronic materials for
wide range of applications such as:
 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
            Various applications
                      Details


   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).
 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 ).
 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.
 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.
There are several conditions that a
thin film solar cell must satisfy in
order to exhibit efficient photovoltaic
e n e r g y c o n v e r s i o n :

 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
Phase change memory
                      Base
crystalline form


                      rapid
                   reversible
                   transition



                                amorphous
 form
             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
                     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
The end

				
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posted:8/13/2011
language:English
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