Single photon sources integrated on Ge Mie resonator fabricated by solid state dewetting

The following Ph.D. thesis summarizes the work that has been made aiming at the fabrication and characterization of quantum emitters integrated inside Ge nanoisland on Si substrates. We choose to induce localized Ge impurities centers inside a thin layer of Al0.25Ga0.75As epitaxially grown on Ge islands acting as dielectric Mie Resonators (MR’s). These centers are working as light sources, capable of single photon emission and quantum entanglement properties. Fabrication of the Ge islands was done by solid state dewetting in an ultra-high vacuum environment, obtaining both amorphous and monocrystalline islands, with sizes ranging from 50 to 500 nm. These islands are also photonic Mie-resonators enhancing light-matter interaction and steering the localized defects emission, acting as dielectric nanoantennas. This thesis exploits molecular beam epitaxy, solid state dewetting and electron assisted lithography for realizing patterned samples. Many different characterization methods have been used to assess the quality of the fabricated samples. We use morphological characterization via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optically, we characterized the Mie resonators by dark field (DF) spectroscopy to ensure their photonic mode appearance. Also, the crystallinity of the Ge seeds was investigated by RAMAN spectroscopy. In the end, the optical response of the samples will be tested by micro and macro Photoluminescence, time-resolved measurements, and auto-correlation measurements to assess the quantum nature of the emission at low temperatures. Towards our goal we faced three main different topics: i) the growth of Ge nanoisland via solid state dewetting, ii) the optimization of the photonic response of semiconductor Mie resonators by engineering the geometry of the substrates, iii) the integration of III-V layers on Ge islands and the observation of interesting associated defects. Each of these aspects is described in detail in chapters 3,4 and 5. During my secondments at UNIFI, I had also been involved in a quite different approach towards the deterministic realization of quantum emitters integrated beneath a glass nanoantenna, an activity which led to article submission, but it is not reported in this thesis.