While he didn't actually invent the diode itself, he was the first to theorize and publish a paper in 1934 explaining the phenomenon of "Zener breakdown". This breakdown occurs when a strong reverse bias is applied to a diode, causing a sudden increase in current.
This theory laid the groundwork for the development of a specific type of diode, later named the Zener diode, that utilizes this breakdown phenomenon for voltage regulation and other applications.
It's important to note that the first practical Zener diodes were developed by Bell Laboratories in the 1950s, based on Zener's theory.