What are the symbols and functions for Zener diode, LED, and photodiode?

Here are the symbols and functions for the electronic components:

A) Zener diode
The Zener diode symbol is:

$$\boxed{ \text{Anode} \longrightarrow \text{|} \text{--} \text{Z} \text{--} \text{|} \longleftarrow \text{Cathode} }$$

Function: A Zener diode is designed to operate in reverse breakdown mode and is primarily used for voltage regulation to maintain a constant voltage across its terminals.

B) Light emitting diode (LED)
The LED symbol is:

$$\boxed{ \text{Anode} \longrightarrow \text{|} \text{--} \triangle \text{--} \text{|} \longleftarrow \text{Cathode} \quad \text{with two arrows pointing away from the diode} }$$

Function: An LED is a semiconductor device that emits light when an electric current passes through it.

C) Photo diode
The photodiode symbol is:

$$\boxed{ \text{Anode} \longrightarrow \text{|} \text{--} \triangle \text{--} \text{|} \longleftarrow \text{Cathode} \quad \text{with two arrows pointing towards the diode} }$$

Function: A photodiode is a semiconductor device that converts light into an electrical current.