Light-emission engineering based on active strain tuning in nanomembranes and photonic metasurfaces

Light-emission engineering is a major topic of fundamental and applied research in photonics. Radiative efficiency enhancement is certainly one of its main targets, for the development of energy-efficient light sources. The radiative properties of semiconductor materials are determined by their band structure, which depends not only on the constituent atoms but also on their spatial arrangement, and therefore can be tuned by the introduction of strain. At the same time, the precise control of the wavefronts plays an important role in engineering the far-field properties of the emitted light, including polarization and directionality. In this regard, photonic metasurfaces, which are artificially textured surfaces composed of periodic subwavelength metal/dielectric nanostructures, can enable light manipulation with unprecedented resolution. They reduce the need for large propagation lengths, due to the ability to change the phase over distances much shorter than the wavelength, which is desirable for the continued miniaturization and integration of photonic devices. Both approaches are investigated in this thesis work. In the area of strain engineering, I have studied tensilely-strained Ge and InGaAs nanomembranes for tunable and enhanced light emission. By virtue of the large threshold of semiconductor nanomembranes for cracking and plastic deformation, high tensile strain can be introduced, which is particularly beneficial for Ge, where the band structure can be converted to direct-bandgap, leading to strong strain-enhanced light emission. My research efforts with Ge nanomembranes have focused on the development of optical cavities, which can provide strong outcoupling at high strain levels. With InGaAs, which is a standard active material for near-infrared diode lasers, I have demonstrated a record-wide spectral tuning range of over 250 nm, which can serve as a promising approach for developing widely tunable lasers. In the area of photonic metasurfaces, I have investigated the use of both plasmonic and dielectric metasurfaces, where subwavelength elements are applied to control the radiation properties of nearby incoherent light emitters, to achieve directional light emission and at the same time enable strong emission-rate enhancements. The key underlying idea is to control spontaneous emission by an arbitrary radiation source via modification of its local dielectric environment (the Purcell effect).2020-07-28T00:00:00