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Sunday, March 15, 2015

#322 How relevant is the concept of "bulk" semiconductor?

The term “bulk” applies to the part of semiconductor in which the periodic potential associated with the atomic structure is assumed to be infinite in all three dimensions. All the key electronic properties of semiconductors, such as for instance carrier mobility, are commonly defined for the bulk portion of the semiconductor material.


The problem is that in the vast majority of the current semiconductor devices the concept of bulk is essentially irrelevant. Whether it is a transistor in logic ICs or a laser diode or a thin-film solar cell the assumption of the infinite periodicity of the potential is invalid. It is simply because films are so thin that the concept of bulk does not apply to the volume of material between its surface at one end and the interface with the other material at the other.



In such material configurations, physical properties of semiconductor, charge carrier transport in particular, are controlled entirely by the surface and near-surface  phenomena and are very different from those defined for the bulk of the same material. For instance, the mobility of electrons in the bulk of silicon (at room temperature) is about 1,500 cm2/Vsec. However, the same mobility of electrons in the strongly confined channel of the Si transistor is typically four or more times smaller which resluts in the propoetionally reduce electrical conductivity of semiconductor.


Posted by Jerzy Ruzyllo at 08:01 AM | 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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