Infrared Nanoantenna-Coupled Rectenna for Energy Harvesting

Energy harvesting from relatively low-temperature heat sources is important in applications where long-term power sources are needed such as deep space radioisotope thermoelectric generators (RTGs). Current solutions exhibit low efficiency, require exotic materials and structures, and direct contact to the heat source. While the infrared rectenna is currently low efficiency, the path exists for high-efficiency solid state devices. We have made a scalable design using standard CMOS processes, allowing for large-area fabrication. This would allow devices to be made on the wafer scale using existing fabrication technology. The rectenna has the advantage of using radiated power, thus it does not require direct contact to the hot source, but instead must only view the source. This will simplify packaging requirements and make a more robust system. The devices are monolithic and thus robust to adverse operating environments. Here we will discuss the rectenna's physics of operation, particularly light coupling into the structure. Incoming light is coupled to a metal-oxide-semiconductor (MOS) tunnel diode via a broad-area nanoantenna. The nanoantenna consists of a subwavelength metal patterning that concentrates the light into the tunnel diode where the optical signal is rectified. Both the nanoantenna and tunnel diode are distributed devices utilizing the entire area of the surface. The nanoantenna also serves as one contact of the tunnel diode. This direct integration of the nanoantenna and diode overcomes the resistive loss limitations found in prior IR rectenna concepts that resembled microwave rectenna designs scaled down to infrared sizes. We will show simulation and experimental results of fabricated devices. Simulations of the optical fields in the tunnel gap are illustrative of device operation and will be discussed. The measured infrared photocurrent is compared to simulated expectations. Far-field radiation power conversion is demonstrated using standard radiometric techniques and correlated with the rectified current response. We discuss thermal modelling of the localized heat generation within the rectenna structure to demonstrate the lack of a thermoelectric response. Lastly, we discuss future directions of work to improve power conversion efficiency.