Document VersionPublisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Johansen, J., Stobbe, S., Nikolaev, I. S., Lund-Hansen, T., Kristensen, P. T., Hvam, J. M., ... Lodahl, P. (2008). Size dependence of the wavefunction of self-assembled InAs quantum dots from time-resolved optical measurements. Physical Review B Condensed Matter, 77(7), 073303.
We study experimentally time-resolved emission of CdSe quantum dots in an environment with a controlled local density of states (LDOS). The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. For the first time, we manage to obtain the oscillator strength of the important class of CdSe quantum dots. The oscillator strength varies weakly with frequency in agreement with behavior of quantum dots in the strong confinement limit. Surprisingly, the measured absolute values are a factor of 5 below theoretically calculated values. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics. * URL: www.photonicbandgaps.com arXiv:0808.3191v1 [physics.optics]
We analyze time-resolved spontaneous emission from excitons confined in self-assembled InAs quantum dots placed at various distances to a semiconductor-air interface. The modification of the local density of optical states due to the proximity of the interface enables unambiguous determination of the radiative and non-radiative decay rates of the excitons. From measurements at various emission energies we obtain the frequency dependence of the radiative decay rate, which is only revealed due to the separation of the radiative and non-radiative parts. It contains detailed information about the dependence of the exciton wavefunction on quantum dot size. The experimental results are compared to the quantum optics theory of a solid state emitter in an inhomogeneous environment. Using this model, we extract the frequency dependence of the overlap between the electron and hole wavefunctions. We furthermore discuss three models of quantum dot strain and compare the measured wavefunction overlap to these models. The observed frequency dependence of the wavefunction overlap can be understood qualitatively in terms of the different compressibility of electrons and holes originating from their different effective masses.
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