They have none of the special skills you’d find in tunnel, Gunn, varicap, Zener, and avalanche diodes, or even LEDs ... The first shows the anode tied to ground through R1 and the cathode ...

The triangle represents the anode, and the line represents the cathode. Forward-biased diode: an ideal diode conducts electricity when a voltage of 0.6V is applied in the forward direction.