Design and Simulation of CMOS-compatible Micro-structured Ge-on-Si Wideband Image Sensor

Abstract

The bandgap limitation of silicon (Si) limits the imaging capabilities of conventional Si CMOS Image Sensors to wavelengths below 1100 nm and thus are inadequate for near-infrared (NIR) / short-wave infrared (SWIR) imaging applications such as metrology, medical imaging and computer vision. Current SWIR image sensors, while capable of detecting wavelengths up to 2000 nm, suffer from several critical drawbacks: they are incompatible with CMOS technology, lack the scalability inherent to CMOS processes, and are prohibitively expensive.

This thesis presents the design and simulation of a CMOS-compatible microstructured germanium-on-silicon (Ge-on-Si) visible and SWIR wideband image sensor. The proposed design uses light-trapping microstructures on the sensor's surface to help enhance the optical efficiency of the infrared-sensitive germanium layer while maintaining compatibility with standard CMOS fabrication techniques. The proposed design is highly scalable, with diffusion-drift and finite-difference time-domain (FDTD) simulations of pixels with 5 um, 15 um and 55 um pitches demonstrating a quantum efficiency of 28% at 1000 nm and 2% at 1300 nm using only a 100 nm Ge layer while also being compatible with the 4T-pixel active pixel sensor (APS) architecture. With future developments using 1 µm Ge layer potentially allowing for QE over 40% across the entire visible+NIR/SWIR spectrum, such a design will enable integrated wideband integrated imaging applications that can utilize the developments of existing CMOS image sensors.