Electro-absorption in Germanium
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To find the optimal wavelength to do the experiment along
with an indication of the strength of the effect we turn to an electroabsorption
spectrum
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Measurement of the electroabsorption is done by attaching
contacts an applying a voltage across the surface (4000 V/cm in the graph
on the right).
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In order to have a large amplification it is important to
have a small absorption. The maximum gain will occur when the absorption
takes a steep plunge.
The above electroabsorption spectrum shows a large negative
change in the absorption coefficient at about .88 eV. This point
will give the maximum diffraction efficiency, thus the incident lasers
should have a photon energy of .88 eV. This corresponds to a wavelength
of 1.4 microns.
