Control of the oscillator strength of the exciton in a single InGaN-GaN quantum dot.
ABSTRACT 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.
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ABSTRACT: Nanorod arrays were fabricated on a blue InGaN/GaN single quantum well (QW) LED wafer using nanoimprint lithography. A regular hexagonal lattice of nanorods was made at a pitch of 2 μm producing single quantum disks in the nanorods with diameter of ˜400 nm. Time integrated micro-photoluminescence was performed to investigate the emission properties of top down processed single nanorods at 4.2 K. Micro-photoluminescence maps were made to study the spatial isolation of the photoluminescence emission, showing a good contrast ratio between nanorods. Excitation power dependent studies show screening of the quantum confined Stark effect for both the unprocessed wafer and the single nanorod. At low excitation powers, localised states appearing as sharp peaks in the photoluminescence spectrum were visible with a density of approximately four peaks per nanorod.Japanese Journal of Applied Physics 08/2013; 52(8). · 1.06 Impact Factor
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ABSTRACT: We report on optical characterization of self-assembled InGaN quantum dots (QDs) grown on three GaN pseudo-substrates with differing threading dislocation densities. QD density is estimated via microphotoluminscence on a masked sample patterned with circular apertures, and appears to increase with dislocation density. A non-linear excitation technique is used to observe the sharp spectral lines characteristic of QD emission. Temporal variations of the wavelength of emission from single QDs are observed and attributed to spectral diffusion. The magnitude of these temporal variations is seen to increase with dislocation density, suggesting locally fluctuating electric fields due to charges captured by dislocations are responsible for the spectral diffusion in this system.Japanese Journal of Applied Physics 08/2013; 52(8). · 1.06 Impact Factor
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ABSTRACT: The quantum confined Stark effect is investigated for the first time in bovine serum albumin (BSA) protected Au8 and Au25 nanoclusters. We observed a red-shift of 63 meV in Au8 nanoclusters upon an increase in pH from 2.14 to 12.0. Such behavior could be well explained in terms of the presence of a linear polar component and a quadratic polarizable component. In contrast, Au25 nanoclusters exhibit more complicated Stark shifts due to their specific core/semiring structure. A plateau of the Stark shift was observed in both absorption and fluorescence, showing an offset of 30 meV. The lifetime measurements confirm that the plateau is due to the screening effect of the semirings in Au25@BSA. Moreover, the dual fluorescent bands of Au25 nanoclusters exhibit two different Stark shifts of 79 and 52 meV, respectively. The experimental data indicate that the Stark shift in both Au8@BSA and Au25@BSA has a significant linear polar component due to their asymmetric structure. This study suggests that gold nanoclusters can become a potentially useful candidate in probing local electric fields and also in pH-sensing in nanoscale environment of biological systems.The Journal of Physical Chemistry C 02/2013; 117(7):3621–3626. · 4.84 Impact Factor