Practitioners have found that diodes have a capacitance
dependent on the reverse polarization voltage.
They improved the effect (guided by experiments)
and made the diode with variable capacity.
Theorists have forced the comparison with a mechanically
variable capacitor (by removing the plates), interpreting
that the applied reverse polarization voltage "widens" the junction
The capacity of the diode consists in the density of the polarities in
the junction p-n.
The direct polarization of the p-n layers increases the conductor quality.
Reverse polarization of the p-n layers increases the quality of the insulator.
Increasing the reverse bias voltage increases the insulator quality of
and decreases the density of the polarities in the junction (the capacity).
So, the variation of the diode capacity consists in the variation of the
of the polarities in the junction, analogous to the variation
of the polarized surface of the "mechanical plates".
The cartoon shows one of the possible shapes.
The polarities in the junction are the forces of attraction
from a distance, which close the oscillating circuits (passage capacity).