The central idea behind integrated photonics is to bring a diversity of optical functionalities on chip to enforce compatibility with electronic circuits and thus profit as much as possible from the enhanced bandwidth offered by the optical transmission of datasignals. At present, the field is rapidly expanding beyond this initial starting point as it became clear that photonic chips have a much broader application potential than initially envisaged, where the development of integrated sensors - ranging from single wavelength systems to fully integrated spectrometers - for (bio)sensing and detection stands out.
Since the preferred wavelength range in which photonic chips operate depends on the application, there is currently an intense search for low-cost, versatile and electrically driven light sources that are compatible with the various materials platforms for integrated photonics. In this respect, colloidal semiconductor nanocrystals or quantum dots (QDs) offer a number of unique properties that make them ideal as light emitters for integrated photonics. Due to size quantization, quantum dots have a bandgap - and thus an emission wavelength - that can be readily tuned by their dimensions. As a result, the same type of material can be made compatibel with a broad range of applications, each requiring different wavelengths and different technology platforms.
However, to make integrated QD-based light sources viable on-chip light sources, electrically driven QD light emitting devices are needed and integration on chip must be demonstrated. This challenge forms the starting point of this master thesis research.
Electrically driven light emission by colloidal quantum dots requires the formation of electron-hole pairs in the quantum dots, for example by direct injection of electrons and holes, that subsequently emits light by radiative recombination. Although this is possible utilizing seperate electron and hole contacts, a relatively straightforward approach that is readily amenable to down-scaling and photonics integration is based on sandwiching three or more quantum dot layers in between two insulators to form a quantum dot capacitor. When driving this capacitor using a sufficiently high, alternating voltage, electron injection from the valence band to the conduction band between quantum dots in successive layers occurs and the resulting electron-hole pairs in the central quantum dot layers emit light.
Together, the physics and chemistry of nanostructures group (prof. Z. Hens) and the photonics research group (prof. D. Van Thourhout) have developed a quantum-dot capacitor based on silicon nitride insulators that is compatible with both the silicon-on-insulator and the silicon nitride integrated photonics platforms. Given this context, the goal of this project is twofold. First, you will use a broad range of driving voltage profiles (sine, step, sawtooth) and analyse the time-dependent displacement current and light emission to understand the details of the operation mechanism of this light emitting quantum-dot capacitor. For this part of the project, you will collaborate intensily with the Liquid Crystals and Photonics group (prof. Kristiaan Neyts). Second, you will develop an integrated version of this quantum dot capacitor, where the emitted light is injected directly into a silicon nitride or silicon waveguide. Here, you will combine simulations, device fabrication and measurements to asses the potential of quantum-dot capacitors for down-scaled photonic light sources. All togeter, this results in a highly multidisciplinary and diverse master thesis project, where you will become familiar with a new class of optical materials (quantum dots), get experienced in electrical and optical characterization, make your first steps in cleanroom processing and characterization of integrated photonic devices and learn to bring together device simulations with experimental results.