Two-photon autocorrelation measurements on a single InGaN/GaN quantum dot.

We report on the use of interferometric autocorrelation measurements to investigate the non-linear absorption processes evident in single InGaN/GaN quantum dots. The near quadratic excitation intensity dependence of the photoluminescence signal in conjunction with the asymmetric collinear autocorrelation trace unambiguously confirms the process as being one involving two photons via an intermediate virtual state. These results highlight the inherently non-linear optical properties of these structures.

Cavity Enhancement of Single Quantum Dot Emission in the Blue.

Cavity-enhanced single-photon emission in the blue spectral region was measured from single InGaN/GaN quantum dots. The low-Q microcavities used were characterized using micro-reflectance spectroscopy where the source was the enhanced blue output from a photonic crystal fibre. Micro-photoluminescence was observed from several cavities and found to be ~10 times stronger than typical InGaN quantum dot emission without a cavity. The measurements were performed using non-linear excitation spectroscopy in order to suppress the background emission from the underlying wetting layer.

Control of the oscillator strength of the exciton in a single InGaN-GaN quantum dot.

We report direct evidence for the control of the oscillator strength of the exciton state in a single quantum dot by the application of a vertical electric field. This is achieved through the study of the radiative lifetime of a single InGaN-GaN quantum dot in a p-i-n diode structure. Our results are in good quantitative agreement with theoretical predictions from an atomistic tight-binding model. Furthermore, the increase of the overlap between the electron and hole wave functions due to the applied field is shown experimentally to increase the attractive Coulomb interaction leading to a change in the sign of the biexcitonic binding energy.