What is a Shockley diode?

Answer 1

An ordinary semiconductor diode uses a P-N junction, but when reverse biased it takes a period of time to remove the current carriers from that junction to create the depletion region that blocks reverse conduction.

A Shockley diode instead uses a P semiconductor-metal junction, which removes the current carriers much faster from the semiconductor allowing the device to switch much faster. It also has a much lower forward bias voltage than an ordinary diode. In many ways it is similar to the previous point contact diodes (a piece of semiconductor like galena or germanium with a metal "cat's whisker" point contact) in operation, but is more reliable and easier to mass produce.