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Optoelectronics has two basic branches: |
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| | Wavelength
(nm) | Typical
Semiconductor |
| Infrared | 880 | GaAlAs/GaAs | | Red |
660 - 633 | GaAlAs/GaAs | Orange
to
Yellow |
612 - 585 | AlGaInP
GaAsP/GaP
GaAsP/GaP |
| Green | 555 | GaP | Blue
to
Ultraviolet | 470 - 395 | GaN/SiC
GaN/SiC
InGaN/SiC |
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1. Light in Þ electrical signal out:
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- Optical sensors as single elements
- "CCD" chips in "megapixel" matrices.
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2. Electricity in Þ light out; in two paradigmatic versions:
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Here we only look at the second branch. |
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The semiconductors of choice are mostly the III-V's, usually in single-crystalline perfect thin films.
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The present day (2008) range of wavelength covers the IR to near UV. |
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Indirect semiconductors like GaP can be used too, if some "tricks" are used. |
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The index of refraction
n=(e)½ and thus the dielectric constant e
become important | |
Typical
Semiconductor |
Dielectric
constant |
Thermal
conductivity
[W/cm · K] |
| Si | 11.9 | 1.5 | | GaAs |
13.1 | 0,45 | | GaP | 11.1 | 1.1 |
| GaN | 8.9 | 1.3 | | SiC |
10 | 5 | | C (Diamond) |
5.8 | 22 |
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Semiconductors have a relatively large index of refraction at photon energies below the bandgap
of n » 3 - 4. | |
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Diamond has the highest n in the visible region |
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The thermal conductivity becomes important
because for generating light one needs power (which we avoided as much as possible for
signal processing with Si!) | |
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Again, diamond has the highest thermal conductivity of all known materials - 5 times
better than Cu! | |
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LED's come as cheap little "indicator" lights and recently also
as replacement for "light bulbs". | |
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Intense white light from LED's becomes possible, Advantages: High efficiencies and
long life time | |
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The key was the "taming" of the GaN material system for blue and UV LED's. |
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LED's based on organic semiconductors (OLED) are rapidly appearing
in OLED based displays. | |
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Advantage: High efficiencies because of active light generation.
Problem: Product life time; sensitivity to air. |
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Semiconductor "Diode" Lasers are high-power" LED's
plus "mirrors" | |
Enabling technology for
CD / DVD / Blue ray / ...
memory technologies! |
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Advantage: Small and cheap.
Problems: Low power, "Quality". |
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© H. Föll (Semiconductor Technology - Script)
