One of the main reasons for the early success of the
tunnel diode was its high speed of operation and the
high frequencies it could handle. This resulted from
the fact that while many other devices are slowed
down by the presence of minority carriers, the tunnel
diode only uses majority carriers, i.e. holes in an
n-type material and electrons in a p-type material.
The minority carriers slow down the operation of a
device and as a result their speed is slower. Also
the tunnelling effect is inherently very fast.
The tunnel diode is rarely used these days and this
results from its disadvantages. Firstly they only
have a low tunnelling current and this means that
they are low power devices. While this may be
acceptable for low noise amplifiers, it is a
significant drawback when they are sued in
oscillators as further amplification is needed and
this can only be undertaken by devices that have a
higher power capability, i.e. not tunnel diodes. The
third disadvantage is that they are problems with the
reproducibility of the devices resulting in low
yields and therefore higher production costs.
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