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What band gaps of which type would we like to have for III-V properties? | ||
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We want to cover regular optics, meaning whatever one can do with visible light. The human eye can perceive wavelengths from 750 nm or 1.65 eV (= red) to 380 nm or 3.26 eV (= violet) | ||
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So we like to have semiconductors with a direct band gap and with every conceivable band gap energy between 1.65 eV and 3.26 eV | ||
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We also know that infra red (IR) optics is important - at the very least for communication via optical fibres. This happens at a wavelength of about 1 500 nm or an energy of about 0.83 eV. This means that we would also like to commandeer direct semiconductors with band gaps ranging from 1.65 eV down to at least 0.8 eV. | ||
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Moreover, we know that there is not only a lot of demand for white light but that there are already "white" LED's in, e.g., flashlights and car headlights. The easiest way to make white light out of monochromatic light (that we will always get from a LED) is to produce ultraviolet light (UV) that is converted to white light via some intermediate fluorescent material like in any "fluorescent" lighting fixture. This means that we also want to have direct semiconductors with band gaps ranging from 3.26 eV up to ??? - well. at least 4 eV. | ||
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Summing up: We need to have direct semiconductors with band gaps ranging from 4eV - 0.8 eV | ||
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What are the requirements for substituting light bulbs by LED's? What is the state of the art? | ||
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First we remember: "Light "bulbs", i.e. lighting fixtures already do exist in many variants.
If we want to replace what has been around for more than a century, we must be cheaper
or better. We can be if we look at the weak points of existing "standard"
lighting with some kind of "bulbs" where light is produced because something is very hot.
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The problem is to have high power (not the same as high efficiency) and all colors. | ||
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State of the art: Look in the Internet and you see: LED lighting is just now starting to replace conventional lighting in special applications. It is expected to go far in replacing general lighting in the next 10 years or so. | ||
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Amend and discuss - the list of optoelectronic products | ||
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The most important optoelectronic products besides LED's are:
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Exercise 2.3-1: All Quick Questions / Class Exercises to 2.3 III-V Semiconductors
© H. Föll (Semiconductor Technology - Script)