Collaborative Research: A Roadmap Toward Terahertz Optoelectronics Using Active Control of Charge Density Waves at Degenerate Semiconductor Interfaces

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The information revolution of the past decades has been driven by unprecedented advances in microprocessor technology and a continuous progression towards smaller, faster and more efficient electronic devices. As a result, remarkable new capabilities have been enabled across vastly different areas of human activity such as telecommunication, computation, finances, national security and space exploration. Despite this progress, the past few years has seen scaling issues associated with electronic interconnect delay times and heat dissipation result in the saturation of microprocessor clock speeds at about 3GHz. Photonic integrated circuits, being the analogue of electronic circuits but with photons substituting for electrons as the information carrier, possess an exceedingly high data-carrying capacity and have the potential to address some of the present bottlenecks in microprocessor technology. However, the dielectric waveguides and interconnects currently used in photonic circuits are limited in size by the fundamental law of diffraction, leading to dimensional mismatch between electronic and photonic components. As a result, their practical implementation in real-world devices, apart from telecommunications, has been substantially hindered. Here we propose a new data processing element, an optoelectronic switch, which assimilates the best characteristics of photonics and electronics. It has the potential to address the current information bandwidth limitations of electronic devices, while simultaneously enabling device sizes that are substantially smaller than traditional photonic elements. A significant impact of this work will be the fostering of cutting-edge research opportunities for graduate and undergraduate students, including from underrepresented groups, implementing a new teaching methodology and pursuing a broader outreach by engaging high school children with fascinating topics in math and sciences. This proposal seeks to develop a new optoelectronic device, referred to as Surface Plasmon Diode, with operation based on active control of charge-density waves propagating at heavily doped (degenerate) semiconductor interfaces. A synergy between theory and experiment will be pursued to gain insight into the complex multi-physics phenomena behind the device operation, including charge transport and recombination at high-gradient, heavily doped pn+- junctions, spatially and time dependent local permittivity variations at the semiconductor interfaces, and thermal effects due to Ohmic heating and electromagnetic energy dissipation. The experimental efforts will lead to Proof of Concept devices based on Silicon-on-Insulator and epitaxially-grown III-V semiconductor materials and compounds. Bulk material growth/fabrication and characterization will inform the theoretical modeling, which in turn will guide the fabrication and experimental characterization of the prototype. The transient response of the devices will be tested using a direct detection method (IR-detector) for modulation rates ranging from low (kHz) to moderate and high frequencies (few MHz up to 3GHz). For data rates higher than 3GHz a new on-chip electro-optical detection will be implemented. These experimental measurements, in conjunction with the theory, will establish the physical limitations and scaling laws governing the device 3dB bandwidth, and establish a clear roadmap toward direct, electro-optical signal modulation at rates down to the picosecond time scale for signal modulation surpassing -10dB and mode sizes that are substantially smaller compared to present-day optoelectronics elements. The proposed research presents a new approach toward fast optical interconnects, circuitry and logic elements and may lead to breakthrough technologies related to integrated optics and electronics, a multibillion dollar industry.