Metal-Semiconductor-Metal Near Infrared Light Detector Based on Epitaxial Ge on Si

Abstract

Due to the ever growing use of optical fibers in communications, for both long distances and local area networks, there is an increasing effort toward the realization of high speed and high efficiency optical detectors, operating in the low-absorption regions (1.3-1.55µm) of silica fibers. Although III-V semiconductors provide high detection efficiency in the range of interest, incorporating them in the well-established Si-based very large scale integration technology is difficult and expensive[ 1 ]. Ge-on-Si structures represents a viable alternative solution for near infrared photodetection, owing to their narrow band gap and full compatibility with silicon technologies. Pure germanium, indeed, represents the best candidate for absorbing in 1.3-1.55 µm photodetectors, due to its direct bandgap of 0.85eV. However, owing to the high lattice mismatch with Si, it is not easy to obtain Ge films with characteristics suitable for integrated electronics: thickness (efficiency of the device), flatness (realization of submicron lithography), defect-free structure (high-speed).