What's the difference between these three different ways of symbolising a generic rectifier diode: solid, outline and outline with connection between anode and cathode?
the original image is from the site below : https://www.tubefr.com/types-de-diodes.html
IEEE Std 315, Graphic Symbols for Electrical and Electronics Diagrams, specifies this symbol for a "Semiconductor diode; semiconductor rectifier diode; metallic rectifier"
The letters in parentheses are not part of the symbol, and the enclosing circle is optional. So, at least in the U.S., the hollow symbols would be non-standard.