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Semiconductor superlattice-type structures may be equipped with multi-well electron transfer capability for high frequency conduction.
English (United States)
This text was extracted from a PDF file.
This is the abbreviated version, containing approximately
86% of the total text.
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Transferred Electron Semiconductor Meso-structures
Semiconductor superlattice-type structures may be equipped with multi-well
electron transfer capability for high frequency conduction.
A superlattice structure of alternating GaAs and Ga(1-x) A1(x)As, grown by
molecular beam epitaxy, doped n-type, behaves as a "potential well" with levels
E(1), E(2) ..., each being the bottom of a two-dimensional sub-band conducting in
the layer plane. These may be expected also to exhibit a two-dimensional hot
electron effect similar to that of ordinary GaAs. By making two layers of different
width close together, since E(1) is approximately proportional to W /-2/, where W
is layer width, the bottoms of the E(1) bands of the layers will differ by an energy,
delta e,typically Approximately 10/-1/ eV. The hot electron effect thus causes a
fraction of the electrons, which will increase with the two-dimensional field, to
transfer from the wide to the narrow band. The narrow layer will have lower two-
dimensional mobility and drift velocities, both by inherent properties and by the
use of modulation doping to put the ions mostly in or near to the narrow layers.
This provides the two conditions necessary for negative differential mobility due
to the transferred-electron effect.
For adjacent layers the transfer rate can be approximately the two-
dimensional energy relaxation rate. Structures with repeated layer pairs could be
fabricated to provide a "bulk" effect with parameter values...