[FarCenter]

Gallium arsenide is widely used as a microwave frequency semiconductor.

Gallium nitride is used for blue wavelength laser diodes and LEDs, e.g. in Blu-ray DVD drives.

Gallium oxide appears to be used as a substrate for gallium nitride, but not as the active semiconductor material.

[ConservativeMind]

Gallium arsenide is the form I was thinking about.

Thank you for that! My memory was from reading computer magazines, long ago.