Current-voltage characteristic of a "crystodyne" junction, a zinc oxide crystal detector junction diode researched beginning in 1923 by Russian radio pioneer Oleg Losev.   The graph shows that the junction has negative resistance (shaded region).   An AC signal applied to the device, biased to the point labelled "wzmacniacz"  within the negative resistance region, will be amplified.    Losev found that these zinc oxide - metal junctions could amplify signals and produce oscillations, and built solid-state radio receivers and oscillators with them, 25 years before the transistor.
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