Rui Zhang

Technology and Device Development for Active/Passive integration on InP-based Membrane on Si (IMOS)

The complexity of photonic integrated circuits has been raised significantly in the last few years, following Moore's law in Photonics. To satisfy the need for even higher complexity, devices have to be made smaller and less power consuming. In this thesis, a new platform (InP-based Membrane on Silicon), which could potentially allow more compact integration capacity for the photonic integration circuits is described. As the early researches, this thesis focuses on the technology development, device design, fabrication and characterization of photonic components for the IMOS platform. The long term goal is to put this membrane on electronic chips (CMOS) to provide the high-speed on-chip data transport so that the Moore's Law can be maintained even further.

First the first generation of IMOS passive components, such as waveguides and MMIs etc with small dimensions are demonstrated with good performance. These are the basic circuitry building blocks for future PICs on IMOS. The good performance and small dimensions of the first generation IMOS passive devices shows potential integrated complexity of IMOS platform. Next since PICs contain both passive and active components, a successful active-passive integration in IMOS is essential. In this thesis an active-passive integration with sub-micrometer active areas based on selective area regrowth technique is developed. The interface between active and passive areas shows good quality in terms of morphology. Moreover, it is found that in the sub-micrometer size active area, the degradation of the active material (InGaAsP QWs) due to processing is limited and controllable. Afterwards in order to realize inject carriers more efficiently into the IMOS active devices, a dielectric aperture is realized by AlInAs oxidation. The influence of temperature and time on the oxidation rate and the surface morphology are investigated. Moreover electrical measurements show that AlInAs oxidation gives an significant increase in the electrical resistance, which make this technique very promising for current confinement functions in the IMOS platform. And this technique developed in this thesis has already been applied to other IMOS active devices.

After the technology development, a line defect photonic crystal cavity is designed and simulated. Optical simulations results show that this cavity gives good performance in terms of quality factor and tolerance to manufacturing imperfections. Moreover, electrical simulation for the layer stack is also proceeded in order to inject the carriers in an efficient manner. Based on the electric simulation results, an optimized layer stack is proposed and it shows much smaller threshold current compared with the original one. In cooperation with SMARTPHOTONICS and Gent university, the manufacturing of the designed laser is pursued. However it turns out that multilayer regrowth is a very difficult process and after several trials only half of one sample survived all the regrowth steps. After the AlInAs oxidation, surprisingly no oxidized AlInAs was observed. It appears that the AlInAs layer is attacked by the HF solution which is used for removing the hard mask (SixNy). Without oxidized AlInAs layer as the current blocking layer, electrically pumped PhC lasers are not possible anymore, since short-circuiting will occur. However, optically pumped PhC lasers are still possible. After the definition of grating couplers, the sample is bonded on a host-Si wafer with BCB. The characterizations show that the devices don't perform as we hoped for. The measurement shows a high optical loss. After checking in the SEM it is seen that many of photonic crystal cavities are damaged because of the force implemented during the bonding process. A further Micro PL measurements didn't detect any emitting light from the remaining QWs which indicates that the QWs have already degraded due to the processing and stop emitting light.

All in all, the results presented in this thesis indicate the possibility of developing photonic components in IMOS for including both active and passive functions. Nevertheless quite a few issues need to be addressed and more technology developments are required to make IMOS a mature platform for the next generation PICs.