  We report on the carrier dynamics in InGaN/GaN disk-in-a-wire quantum dots
with precisely controlled location and structural parameters, including
diameter, thickness and material composition. We measured the time-integrated
and time-resolved spectra and the second-order correlation function of the
photoluminescence from quantum dots with diameters ranging from 19 nm to 33 nm
at temperatures of 10 K to 120 K. The influence of the small fluctuations in
structural parameters, most importantly the quantum dot thickness, on the
optical properties are also investigated through statistical correlations among
multiple optical properties of many individual quantum dots. We found that in a
single dot the strain-induced polarization field and the strain relaxation at
the sidewall form a potential barrier to protect the exciton from reaching the
sidewall surface. However, the exciton can overcome this potential barrier and
recombine nonradiatively at the surface through two mechanisms: tunnelling
through the barrier quantum mechanically and hopping over the barrier by
attaining sufficient thermal energy. The former (latter) mechanism is
temperature insensitive (sensitive) and dominates nonradiaitve exciton decay at
low (high) temperatures. We also found that despite the good uniformities in
structural parameters, all optical properties still exhibit inhomogeneities
from dot to dot. However, all these inhomogeneities can be modeled by simply
varying the potential barrier height, which also explains the observed
correlation curves among all optical properties. Finally, we found that the
biexciton-to-exciton quantum efficiency ratio, which determines the probability
of multi-photon emission, can be tuned by adjusting the potential barrier
height and the temperature, suggesting a new way to achieve single photon
emission at high temperatures.
