  Efficient generation of single photons on demand at a high repetition rate is
a key to the practical realization of quantum-communication networks and
optical quantum computations. Color centers in diamond are considered to be the
most promising platform for building such single-photon sources owing to the
outstanding emission properties of color centers at room temperature. However,
their efficient electrical excitation remains a challenge due to the inability
to create a high density of free electrons in diamond. Here, we show that using
the self-gating effect in a diamond p-i-n diode, one can overcome the doping
problem and inject four orders of magnitude more carriers into the i-region of
the diamond diode than the doping of the n-region allows. This high density of
free electrons can be efficiently used to boost the single-photon
electroluminescence process and enhance the brightness of the single-photon
source by more than three orders of magnitude. Moreover, we show that such a
high single-photon emission rate can be achieved at exceptionally low injection
current densities of only 0.001 A/mm$^2$, which creates the backbone for the
development of low-power and cost-efficient diamond quantum optoelectronic
devices for quantum information technologies.
