SOI-based optical devices allow for back-side illumination, and are compatible with standard CMOS processing. The absorption spectrum of SOI substrates can be tailored via modifying the device-Si layer’s thickness and doping concentration. We have demonstrated that wide spectral responsivity can be achieved in photodetectors that use a simple metal-insulator-semiconductor (MIS) structure (based on two-layer dielectric stack: a SiO2 layer, and a high-k film such as HfO2) fabricated on SOI substrates. Additionally, these devices have lower dark current, compared to their metal-semiconductor (MS) counterparts. For a moderately thick device-Si layer (~ 3 ?m), the absorption in the ultraviolet (UV) regime is quite large; and the absorption in the near-infrared (NIR) regime is smaller. We have demonstrated enhanced responsivity (in NIR regime) in such MIS photodetectors due to the incorporation of Au-nanoantennas at the optical input port. These nanoantennas modify the propagation of the input optical signals, serving as an effective anti-reflection coating in the NIR wavelength range. In this regime, strong local field enhancements are present at the Au-nanodisk/device interface, further contributing to the detector optical response. The optimal antenna design and the photo-response enhancements have been calculated using detailed FDTD simulations. The maximum responsivity enhancement, 40%, was obtained at 780 nm, while at wavelengths shorter than 720 nm, responsivity is reduced due to absorption losses in the Au-nanoantennas.
Revathy Padmanabhan received the B.E. degree in electronics and communication engineering from Visvesvaraya Technological University, Belgaum, India, in 2006, and the Ph.D. degree in electrical communication engineering (in collaboration with the Centre for Nano Science and Engineering) from the Indian Institute of Science, Bangalore, India, in 2014. She is currently a Postdoctoral Fellow at the Andrew and Erna Viterbi Faculty of Electrical Engineering, Technion–Israel Institute of Technology, Haifa, Israel. From July 2006 to July 2008, she was with IBM India, Bangalore, where she worked as a Systems Engineer. Her current research interests include high-k materials for MIM capacitor applications, and CMOS-compatible photodetectors and varactors.