  We show over 100-fold enhancement of the exciton oscillator strength as the
diameter of an InGaN nanodisk in a GaN nanopillar is reduced from a few
micrometers to less than 40 nm, corresponding to the quantum dot limit. The
enhancement results from significant strain relaxation in nanodisks less than
100 nm in diameter. Meanwhile, the radiative decay rate is only improved by 10
folds due to strong reduction of the local density of photon states in small
nanodisks. Further increase in the radiative decay rate can be achieved by
engineering the local density of photon states, such as adding a dielectric
coating.
