From left to right- Schottky diode, Conventional diode, Shockley diode, and Zener diode.
Schottky- High power rectification. <.3V
Conventional- Standard rectification. .3V-.6V
Shockley- Low breakdown voltage(DIAC only for DC) .6V-2V
Zener- Higher breakdown voltage, low reverse voltage 1v<
