The side of a diode that is n-doped, or the n-region. By standard notation, this is generally considered the “negative” side of a diode, except with Zener diodes, which are backwards.
The n region of a diode.
Electronic Devices : Conventional Current Version, 9th Edition by Thomas L. Floyd
The n side of the diode is called the cathode.
Grob’s Basic Electronics, 11th Edition by Mitchel E. Schultz
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic cathode current departs also means that electrons flow into the device's cathode from the external circuit.
The electrode through which conventional current flows the other way, into the device, is termed an anode.