Mitigation of Thermal Resistance in High Power Photodiodes as a Means to Increase Device Performance

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

Title: Nanoscale interfacial heat transfer engineering to increase high power photodiode device performance Non-technical: Analog optical links are being deployed in a growing number of applications. Examples include cable television, beam-forming networks for phased array antennas, "antenna remoting" for radar, and local oscillator distribution for radio telescopes such as the Atacama large millimeter/sub-millimeter array in Chile, one of the largest radio telescopes in the world. These analog links can be viewed as replacements for conventional electrical cables or waveguides, which are often impractical due to their high loss and limited bandwidth. High-power, high linearity photodiodes are essential components for these optical links since they can enable high link gain, low noise figure, and high spurious free dynamic range. However, the efficiency and output power of strongly limited by thermal failure. Thermal failure is commonly addressed by packaging the devices on high thermal conductivity submounts/substrates. While this approach often leads to gains in device output, there are additional sources of thermal resistance in the photodiode layers and interfaces must be mitigated to further increase the efficiency of devices. This introduces the overarching theme of this proposal: quantifying the thermal resistance at each layer and interface of a high-power photodiode, and using that information to make informed design choices, applicable to a large class of high power devices, that will lead to improved device performance. The far reaching societal implications from improving high power device performance from a "thermal first" material design and processing prospective will lead to novel material solutions and processes for all electronic devices to mitigate thermal transport from the nanoscale level during architecture design, which will lead to reduction of wasted energy via more efficient electronics via better usage of portable power and reduction in plug loads. Furthermore, this proposed work will be integrated into various coordinated outreach activities, which are focused on increasing science learning and hands-on activities in K-12 classrooms through the NanoDays program, high school teacher and student summer research in University Labs and conference organization and attendance, with particular focus on under-represented groups and low-income schools around Virginia. Technical: The overarching technical theme of this proposal is to quantify the thermal resistance at each layer and interface of a modified uni-traveling carrier photodiode, and use that information to make informed material design choices, applicable to a large class of high power devices. This work will measure and quantify the process/thermal property relationships using a hypothesis-driven study of material choice and processing during device fabrication to identify feasible routes for thermal mitigation via layer-by-layer thermal analysis. The research is driven by the following hypothesis: the sources of thermal resistance in high-power devices can be determined and reduced to dramatically increase device performance through careful choice of materials, design of interfaces, and processing conditions. Therefore, in testing thermal properties of device-grade thin films and film/substrate interfaces, this project will also advance the understanding of electron and phonon transport in bonded films and metal/non-metal interfaces, with particular focus on device-level structures and the role of defects, microstructure and processing conditions. From the proposed nanoscale thermal transport measurements conducted with time-domain thermoreflectance, a new device will be designed and tested that will redefine the state of the art power output for high frequency photodiodes. The power gain realized in this specific photodiode will guide the choices for an entire class of high power devices and set the standard for material and processing choices. The approach will create novel, feasible material solutions to improve device performance based on a better understanding of nanoscale electron and phonon thermal transport in the bonding layers, bonded interface and sub-mount contact layers, which will directly translate to record output powers in modified uni-traveling carrier photodiodes.