  A procedure to achieve the density-controlled growth of gold-catalyzed InP
nanowires (NWs) on (111) silicon substrates using the vapor-liquid-solid method
by molecular beam epitaxy is reported. We develop an effective and mask-free
method based on controlling the number and the size of the Au-In catalyst
droplets in addition to the conditions for the NW nucleation. We show that the
NW density can be tuned with values in the range of 18 {\mu}m-2 to < 0.1
{\mu}m-2 by the suitable choice of the In/Au catalyst beam equivalent pressure
(BEP) ratio, by the phosphorous BEP and the growth temperature. The same degree
of control is transferred to InAs/InP quantum dot-nanowires, taking advantage
of the ultra-low density to study by micro-photoluminescence the optical
properties of a single quantum dot-nanowires emitting in the telecom band
monolithically grown on silicon. Optical spectroscopy at cryogenic temperature
successfully confirmed the relevance of our method to excite single InAs
quantum dots on the as-grown sample, which opens the path for large-scale
applications based on single quantum dot-nanowire devices integrated on
silicon.
