  Quantum technologies require robust and photostable single photon emitters
(SPEs) that can be reliably engineered. Hexagonal boron nitride (hBN) has
recently emerged as a promising candidate host to bright and optically stable
SPEs operating at room temperature. However, the emission wavelength of the
fluorescent defects in hBN has, to date, been shown to be uncontrolled. The
emitters usually display a large spread of zero phonon line (ZPL) energies
spanning over a broad spectral range (hundreds of nanometers), which hinders
the potential development of hBN-based devices and applications. We demonstrate
bottom-up, chemical vapor deposition growth of large-area, few layer hBN that
hosts large quantities of SPEs: 100 per 10x10 {\mu}m2. Remarkably, more than 85
percent of the emitters have a ZPL at (580{\pm}10)nm, a distribution which is
over an order of magnitude narrower than previously reported. Exploiting the
high density and uniformity of the emitters, we demonstrate electrical
modulation and tuning of the ZPL emission wavelength by up to 15 nm. Our
results constitute a definite advancement towards the practical deployment of
hBN single photon emitters in scalable quantum photonic and hybrid
optoelectronic devices based on 2D materials.
