Simulation and optical characterization of efficient light-emitting metallo-dielectric micro- and nanopillars

Currently there is a large boost in developing photonic technologies for computing as they promise high speed and low energy consumption. Nanoscale light sources might play a key role for such photonic integrated circuits, which may replace electronic chips one day. Recent experimental implementations include nanolasers, which typically require complex nanostructures for lasing operation, e.g. realized via photonic crystals, metallo-dielectric or plasmonic cavities. Here alternatives to nanolasers are studied - nanolight-emitting diodes (nanoLEDs). The main advantages are that these do not require high quality factor cavities needed to reach a lasing threshold, thus making nanoLEDs less sensitive to fabrication imperfections. By engineering nanoLEDs using nanocavities, the spontaneous emission rate can be increased substantially as compared with the bulk material as described by the Purcell effect. NanoLEDs using cavities smaller than the emitted wavelength, show great potential due to their unique features such as ultra-small footprint, high-speed modulation and unprecedent low energies budget. In this thesis, the optical properties of a dielectric encapsulated semiconductor AlGaAs/GaAs/AlGaAs nanopillars with or without a metal cavity will be investigated, both theoretically and experimentally. The theoretical part includes the analysis of metallo-dielectric micro- and nanopillar structures using 3D-FDTD simulations and the study of the radiative recombination taking the Purcell effect into account. The optical characterization includes the study of the emission properties using micro-photoluminescence and time-resolved photoluminescence techniques. From these results, the expected internal quantum efficiency (IQE) values are analyzed and the potential of these structures for the design of efficient nanoLED sources is discussed. The results are discussed in the perspective of the development of highly efficient nanoLEDs at room-temperature for future integrated photonics circuits

Enhancement of the optical gain in GaAs nanocylinders for nanophotonic applications

Semiconductor nanolasers based on micro disks, photonic crystal cavities, and metallo-dielectric nanocavities have been studied during the last decade for on-chip light source applications. However, practical realization of low threshold, room temperature operation of semiconductor nanolasers is still a challenge due to the large surface-to-volume ratio of the nanostructures, which results in low optical gain and hence higher lasing threshold. Also, the gain in nanostructures is an important parameter for designing all-dielectric metamaterial-based active applications. Here, we investigate the impact of p-type doping, compressive strain, and surface recombination on the gain spectrum and the spatial distribution of carriers in GaAs nanocylinders. Our analysis reveals that the lasing threshold can be lowered by choosing the right doping concentration in the active III-V material combined with compressive strain. This combination of strain and p-type doping shows 100x improvement in gain and ~5 times increase in modulation bandwidth for high-speed operation.Comment: 19 pages, 6 figure

Purcell Effect in the Stimulated and Spontaneous Emission Rates of Nanoscale Semiconductor Lasers

Nanoscale semiconductor lasers have been developed recently using either metal, metallo-dielectric or photonic crystal nanocavities. While the technology of nanolasers is steadily being deployed, their expected performance for on-chip optical interconnects is still largely unknown due to a limited understanding of some of their key features. Specifically, as the cavity size is reduced with respect to the emission wavelength, the stimulated and the spontaneous emission rates are modified, which is known as the Purcell effect in the context of cavity quantum electrodynamics. This effect is expected to have a major impact in the 'threshold-less' behavior of nanolasers and in their modulation speed, but its role is poorly understood in practical laser structures, characterized by significant homogeneous and inhomogeneous broadening and by a complex spatial distribution of the active material and cavity field. In this work, we investigate the role of Purcell effect in the stimulated and spontaneous emission rates of semiconductor lasers taking into account the carriers' spatial distribution in the volume of the active region over a wide range of cavity dimensions and emitter/cavity linewidths, enabling the detailed modeling of the static and dynamic characteristics of either micro- or nano-scale lasers using single-mode rate-equations analysis. The ultimate limits of scaling down these nanoscale light sources in terms of Purcell enhancement and modulation speed are also discussed showing that the ultrafast modulation properties predicted in nanolasers are a direct consequence of the enhancement of the stimulated emission rate via reduction of the mode volume.Comment: 12 pages, 5 figure

Impact of p-doping, strain and surface recombination on optical gain in GaAs nanocylinders

Semiconductor nanolasers based on micro disks, photonic crystal cavities, and metallo-dielectric nanocavities have been studied during the last decade for on-chip light source applications. However, practical realization of low threshold, room temperature operation of semiconductor nanolasers is still a challenge due to the large surface-to-volume ratio of the nanostructures, which results in low optical gain and hence higher lasing threshold. Also, the gain in nanostructures is an important parameter for designing all-dielectric metamaterial-based active applications. Here, we investigate the impact of p-type doping, compressive strain, and surface recombination on the gain spectrum and the spatial distribution of carriers in GaAs nanocylinders. Our analysis reveals that the lasing threshold can be lowered by choosing the right doping concentration in the active III-V material combined with compressive strain. This combination of strain and p-type doping shows 100x improvement in gain and ~5 times increase in modulation bandwidth for high-speed operation