  Single photon emitters play a central role in many photonic quantum
technologies. A promising class of single photon emitters consists of atomic
color centers in wide-bandgap crystals, such as diamond silicon carbide and
hexagonal boron nitride. However, it is currently not possible to grow these
materials as sub-micron thick films on low-refractive index substrates, which
is necessary for mature photonic integrated circuit technologies. Hence, there
is great interest in identifying quantum emitters in technologically mature
semiconductors that are compatible with suitable heteroepitaxies. Here, we
demonstrate robust single photon emitters based on defects in gallium nitride
(GaN), the most established and well understood semiconductor that can emit
light over the entire visible spectrum. We show that the emitters have
excellent photophysical properties including a brightness in excess of 500x10^3
counts/s. We further show that the emitters can be found in a variety of GaN
wafers, thus offering reliable and scalable platform for further technological
development. We propose a theoretical model to explain the origin of these
emitters based on cubic inclusions in hexagonal gallium nitride. Our results
constitute a feasible path to scalable, integrated on-chip quantum technologies
based on GaN.

Materials Science;Mesoscale and Nanoscale Physics;Optics