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Sunday, May 15, 2016

#345 Semiconductor material engineering, part. III

Besides affecting width of the energy gap, distribution of energy states within the energy bands of semiconductor affects also the mechanism of electron transition from the higher energy levels in the conduction band to the lower energy levels in the valence band in the process of charge carriers recombination.


In the case of semiconductors featuring direct bandgap the energy released in the process of electron recombination is in the form of light (photon) emitted by the material. In contrast, in the indirect bandgap semiconductors the same energy is released into semiconductor crystal mostly in the form of vibrational energy (phonon).


This inherent characteristic of the energy gap is predetermined for any semiconductor featuring set chemical composition. But when you start altering chemical compositions of some compound semiconductor the change of bandgap’s type from direct to indirect (or vice versa) is entirely possible.


Taking GaAs as an example, but not in combination with Al as in the previous blog, but with phosphorous (P). A peculiar property of the Ga-As-P material system is that at certain composition between GaAs and GaP the energy gap changes form direct to indirect making  material which is initially suitable for  light emitting devices  to the one which is entirely ineffective in this application.


And that’s yet another example of what manipulation of the chemical composition of semiconductor can bring about.


Posted by Jerzy Ruzyllo at 12:33 PM | Semiconductors | Link is the personal blog of Jerzy Ruzyllo. With over 35 years of experience in academic research and teaching in the area of semiconductor engineering (currently holding position of a Distinguished Professor of Electrical Engineering and Professor of Materials Science and Engineering at Penn State University), he has a unique perspective on the developments in this progress driving technical domain and enjoys blogging about it.

With over 2000 terms defined and explained, Semiconductor Glossary is the most complete reference in the field of semiconductors on the market today.

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