Materials World Network: Complex oxides for heterogeneous optoelectronic integration

This project proposes to bring new functionalities to semiconductor systems by using materials research to identify paths of integration for complex oxide claddings onto semiconductor structures, such as waveguides. As the US PI, Stadler from Minnesota brings to the collaboration an expertise in oxide integration with recently proven processes for controlling thermal strain to achieve high-quality oxides on semiconductor platforms. As the UK PI, Hutchings from Glasgow brings to the collaboration an expertise in III-V semiconductor fabrication and processing, including design of quasi phase matching to enable cancellation of structure birefringence effects. Together, this team will add new materials to the palettes of designers interested in electronics, photonics, sensors, and unimagined future areas. To begin, this collaboration will focus on adding magneto-optical (MO) and electro-optical (EO) properties that are orders of magnitude greater than currently available to semiconductors by integrating both doped yttrium iron garnet (YIG) and lithium niobate (LNO), respectively, onto III-V structures.

Intellectual Merit.
With motivations such as source-integrated photonic integrated circuits (PICs) and electronically-reconfigurable opto-electronic integrated circuits (OEICs), there has been heated work on adding MO and EO materials to semiconductor platforms. However, most researchers in these areas have focused on device design and have been frustrated by the difficulty involved in complex oxide integration where there exists a need for thermal crystallization methods together with thermal expansion mismatch, substrate dissociation, and interfacial diffusion. Here, we propose to use the classic materials tetrahedron (processing, structure, properties, performance) to rapidly converge on a solution involving controlled strain and interfaces using buffer layers and seed layers (both~10nm), oxide patterning, and rapid thermal annealing for minimized thermal treatment. Subsequent doping in thicker films can be used to meet specifications of maximized MO or EO activity, and while the processing is optimized to obtain the optimized film crystal structures. The optical, magnetic, and electronic properties will be characterized to analyze the optimal structures and compositions, and the materials performance will be tested on simple waveguide structures designed to cancel the effects of the structures themselves. The fundamentals of this process have been proven with undoped YIG in a preliminary collaboration between Stadler and Hutchings. This project will determine if their process can be extended to the integration of doped YIG (promising 10-100x increase in MO activity) and of LNO. In the case of MO integration, non-reciprocity will finally be realized without the high-power options currently being proposed by some researchers. This means that, analogous to electronic diodes, isolators will be possible and optical sources can be integrated with PICs- a development that will revolutionize photonics immediately and other fields as designers begin to dream. Integrated ferroelectric oxides will also unlock doors to never explored EO functionality in both near and long term applications, such as active frequency modulation and reconfigurable photonics.

Broader Impacts.
In addition to the scientific benefits of combining III-V platforms with complex oxides, value will be added by this US-UK collaboration in a broader sense. Online group meetings will utilize web-meetings with UMConnect and PaperShow to enable attendees to see each other's faces, writings and slides and to hear each other's voices. Individual skype video-conferencing between students for real-time experimental exchange will allow rapid advances of this research. The findings of this online interaction will be disseminated via the MRS materials education symposia. We also have planned for student/junior researcher exchange.

The proposed materials research aims to develop a set of compatible deposition and fabrication technologies for incorporating functional complex oxide layers alongside diode lasers and other active elements within a monolithic optoelectronic platform. This includes both nonreciprocal optical elements, as exploited in optical isolators and circulators, and ferroelectric elements which can be exploited in high speed electro-optic modulation and nonlinear optical frequency conversion. The techniques we develop will impact on the international community of
researchers in the field of integrated optoelectronics, covering Europe, North America and the Pacific Rim.

These topics have a potential substantive commercial impact across a number of sectors. In the telecommunications sector there is a real need for robust, low cost, low-power polarisation control and optical isolation, particularly in fibre-to-the-home and metro-networks. The commensurate increase in data rates afforded by such devices will be of benefit to the Digital Economy. The technology developed here has a wide range of applications in guided-wave and free-space optical sensor applications. This has the potential to impact the life sciences and medical fields, environmental monitoring, industrial process monitoring, military and security sensing applications. Other example applications include LIDAR for civilian traffic monitoring and on-board collision avoidance systems and ring laser gyroscopes demonstrate the capacity of
enhanced sensing capability for transport. In addition to the commercial benefits of such sensing applications, they have the capacity to make positive contributions to the nation's health (through health monitoring), quality of life (through environmental monitoring) and to the public infrastructure (for example, transport).

This materials research is focussed on the fundamental technology at Technology Readiness Level 1--2. Nevertheless some applications are capable of being implemented in the timescale of 3--8 years and we have already identified some appropriate potential industrial partners. Other applications will have an indirect route to adoption as the technology described here provides the platform for specific sensors, and we would expect a timescale of 10--15 years in some cases.

This research also provides a vehicle for research staff to acquire and refine technical and generic research skills, who should subsequently make a positive contribution to the nation's workforce in the sectors described above.