Search

Spin-controlled lasers are highly interesting photonic devices and have been shown to provide ultra-fast polarization dynamics in excess of 200 GHz. In contrast to conventional semiconductor lasers their temporal properties are not limited by the intensity dynamics, but are governed primarily by the interaction of the spin dynamics with the birefringent mode splitting that determines the polarization oscillation frequency. Another class of modern semiconductor lasers are high-beta emitters which benefit from enhanced light-matter interaction due to strong mode confinement in low-mode-volume microcavities. In such structures, the emission properties can be tailored by the resonator geometry to realize for instance bimodal emission behavior in slightly elliptical micropillar cavities. We utilize this attractive feature to demonstrate and explore spin-lasing effects in bimodal high-beta quantum dot micropillar lasers. The studied microlasers with a beta-factor of 4% show spin-laser effects with experimental polarization oscillation frequencies up to 15 GHz and predicted frequencies up to about 100 GHz which are controlled by the ellipticity of the resonator. Our results reveal appealing prospects for very compact, ultra-fast and energy-efficient spin-lasers and can pave the way for future purely electrically injected spin-lasers enabled by short injection path lengths.

The electronic structure of strain-engineered single InGaAs/GaAs quantum dots emitting in the telecommunication O band is probed experimentally by photoluminescence excitation spectroscopy. Observed resonances can be attributed to p-shell states of individual quantum dots. The determined energy difference between s-shell and p-shell shows an inverse dependence on the emission energy. The experimental data are compared with the results of confined states calculations, where the impact of the size and composition in the investigated structures is simulated within the 8-band $\mathbf{k}\cdot\mathbf{p}$ model. On this basis, the experimental observation is attributed mainly to changes in indium content within individual quantum dots, indicating a way of engineering and selecting a desired quantum dot, whose electronic structure is the most suitable for a given nanophotonic application., Comment: 15 pages, 3 figures, improved manuscript text and figures

Hereby, we present a comprehensive experimental and theoretical study of the electronic structure and optical properties of excitonic complexes in strain-engineered InGaAs/GaAs quantum dots (QDs) grown by metal-organic chemical vapour deposition and emitting at the 1300 nm telecommunication window. Single QD properties have been determined experimentally for a number of nanostructures by means of excitation-power-dependent and polarization-resolved microphotoluminescence and further compared with the results of confined states calculations employing the 8-band kp theory combined with the configuration interaction method. The origin of excitonic complexes has been exemplarily confirmed based on magnetooptical and correlation spectroscopy study. Understanding the influence of structural parameters and compositions (of QDs themselves as well as in the neighbouring strain reducing layer) allows to distinguish which of them are crucial to control the emission wavelength to achieve the telecommunication spectral range or to affect binding energies of the fundamental excitonic complexes. The obtained results provide deeper knowledge on control and on limitations of the investigated structures in terms of good spectral isolation of individual optical transitions and the spatial confinement that are crucial in view of QD applications in single-photon sources of high purity at telecom wavelengths.

We report on the realization of micropillars with site-controlled quantum dots (SCQDs) in the active layer. The SCQDs are grown via the buried stressor approach which allows for the positioned growth and device integration of a controllable number of QDs with high optical quality. This concept is very powerful as the number and the position of SCQDs in the cavity can be simultaneously controlled by the design of the buried stressor. The fabricated micropillars exhibit a high degree of position control for the QDs above the buried stressor and $Q$-factors of up to 12000 at an emission wavelength around 930 nm. We experimentally analyze and numerically model the cavity $Q$-factor, the mode volume, the Purcell factor and the photon-extraction efficiency as a function of the aperture diameter of the buried stressor. Exploiting these SCQD micropillars, we experimentally observe the Purcell enhancement in the single-QD regime with $F_P$ = 4.3 $\pm$ 0.3., Comment: 5 pages, 4 figures