Kihyun Choi

Room-temperature triggered single photon emission from a III-nitride site-controlled nanowire quantum dot.

We demonstrate triggered single photon emission at room temperature from a site-controlled III-nitride quantum dot embedded in a nanowire. Moreover, we reveal a remarkable temperature insensitivity of the single photon statistics, and a g((2))[0] value at 300 K of just 0.13. The combination of using high-quality, small, site-controlled quantum dots with a wide-bandgap material system is crucial for providing both sufficient exciton confinement and an emission spectrum with minimal contamination in order to enable room temperature operation. Arrays of such single photon emitters will be useful for room-temperature quantum information processing applications such as on-chip quantum communication.

Photoluminescence from highly excited AlN epitaxial layers

Excitonic optical properties of AlN epitaxial layers have been studied by means of photoluminescence and optical reflectance spectroscopies. The binding energy of free excitons was estimated to be 57meV on the basis of the energy separation between the n=1 ground and n=2 excited states. In addition, the luminescence line due to radiative recombination of biexcitons was observed under high density excitation. The energy separation between free-exciton luminescence and biexciton luminescence was 19meV, which corresponded to the binding energy of biexcitons. Therefore, the ratio of the biexciton binding energy to the exciton binding energy was approximately 0.33.

Strong exciton confinement in site-controlled GaN quantum dots embedded in nanowires

The optical properties of site-controlled single GaN quantum dots (QDs) embedded in nanowires are presented. These properties are largely determined by a strong carrier confinement due to the small size of the dots (0.5 ∼ 1 nm in height). The QDs emit in the deep-ultraviolet region of the electromagnetic spectrum and exhibit the biexciton binding energy of 52 meV, which is the largest value ever reported in III-V semiconductor QDs. Furthermore, the dots luminesce at room-temperature and have short exciton decay times of ∼300 ps due to an increased oscillator strength. These findings indicate that these site-controlled QDs are promising for various applications in quantum information devices.

Probing the Excitonic States of Site-Controlled GaN Nanowire Quantum Dots

We report the detection of fully confined excited states and the zero-absorption region of individual site-controlled GaN/AlGaN nanowire quantum dots using photoluminescence excitation spectroscopy, which provides evidence of the true zero-dimensional discrete density of states of such quantum dots. Because of the strong quantum confinement in these dots, the p-shell, d-shell, and even higher energy (including some f-shell) states of a single quantum dot are observed, which provides unprecedented insight into the electronic structure. Several emitters are measured and used to build up an average picture of the electronic structure of a single quantum dot via comparison to theoretical simulations.

Temperature Dependent Photoluminescence Excitation Spectroscopy of GaN Quantum Dots in Site Controlled GaN/AlGaN Nanowires

Photoluminescence excitation spectroscopy is performed on a single GaN quantum dot embedded in a core shell type GaN/AlGaN nanowire. The temperature dependence of the photoluminescence excitation spectrum is presented, revealing the expected temperature dependent shift in both the exciton ground and excited states. The states are further characterised by comparison to 8-band kp calculations.

Linearly polarized single photons from small site-controlled GaN nanowire quantum dots

We report and discuss the origins of linearly polarized single photon emission from site-controlled GaN nanowire quantum dots. The observed single photon emission reveals almost complete linear polarization, in agreement with studies in the literature, which could be of use for applications such as quantum key distribution.