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Structure and size matter! |
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| Typical Si wafer: |
300 mm, 850 µm thick, perfect single crystal |
| Solar cell: Si |
- Single crystalline, bulk.
- Poly crystalline, large grain, bulk.
- Polycrystalline, micro grain, "thick" film
- Polycrystalline, nano grain, thin film.
- Amorphous (plus H), thin film
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Mostly we need single crystals, as perfect (and as large) as possible |
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Either in bulk, or thin films | |
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If thin film, substrates matter. |
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For some applications (solar cell , LCD, ...) polycrystalline or amorphous
semiconductors are used. | |
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"CIGS" or CdTe for solar cells. |
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Amorphous or poly-Si for LCD transistor matrix. |
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Important elemental semiconductors are Si
and marginally Ge. | |
| Some important Properties | Remarks |
| Lattice type, lattice constant | Structure independent |
| Melting point, diffusion constants |
| Bandgap type and energy | | Dielectric constant |
| Thermal expansion coefficient | | Doping range |
Structure dependent |
Transport of electron / holes
(mobility, life time, diffusion length, .. |
| Unwanted levels in bandgap |
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Forget Se, C, P, As and B. |
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Compound semiconductors are important. |
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Group IV and compounds: SiGe, SiC. |
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III-V compounds (Al, Ga, In) - (N, P, As,
Sb). Important GaAs, GaxAl1-xAs, GaP, InP, .. |
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| Chalkogenides
AxBy(S, Se, Te)2. Important "CIGS" = CuInxGa1-xSe2. |
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"Newcomers" like organic semiconductors, Metal oxides (e.g. TiO2). |
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Properties matter! Some properties are rather independent of the structure (=
defects), others can be structure sensitive | |
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What counts in the end are products that sell and make a profit! |
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| Integrated circuits, Solar cells, Liquid crystal displays, Micro electronic and mechanical
systems, Light emitting diodes, (Diode) Lasers, Sensors, ... |
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Besides the direct semiconductor products, there are also products that contain semiconductors
(PC's, Cars, TV's, any modern machine,...) and products that are needed to make semiconductor products (crystal growers,
ovens, plasma etchers, ion implanters, ..). | |
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© H. Föll (Semiconductor Technology - Script)
