Tech Briefs
(a) A cross-sectional schematic of the GeSn p-i-n photodiode. (b) Dark I-V characteristics of the three samples. (c) Spectral response of the samples measured at zero bias. (d) Calculated responsivity of the samples.

Enhancing the performance of GeSn p-i-n photodiodes using gold metal nanostructures.

The goal of this research project was to advance the science and technology of silicon-based photonic devices using SiGeSn heterostructures. Such devices work in mid-IR spectral range and form the foundation for mid-IR photonics that enable on-chip systems for applications ranging from vibrational spectroscopy, chem/bio sensing, medical/health uses, to environmental monitoring. This project was mostly directed toward improving GeSn detectors with the use of surface plasmons induced by carefully designed metal nanostructures. The goal was to replace the current mid-IR detectors that are usually photodiodes made from narrow bandgap III-V or II-VI semiconductor compounds such as InGaAs, InSb, HgCdTe (MCT) or type-II In-GaAs/InGaSb superlattice. These photodiodes are incompatible with the CMOS process and cannot be easily integrated with Si electronics. The GeSn mid-IR detectors developed in this project are fully compatible with the CMOS process.

Beginning with GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained, the strategy is to use the surface plasmon effect to enhance the optical field in the GeSn active region, which leads to increased absorption of incident photons and creates electron-hole pairs that contribute to the electric current that can be detected. Specifically, the use of a gold metal film perforated with a two-dimensional subwavelength hole array as the plasmonic structure to be deposited on top of the GeSn p-i-n photodetector was considered. Such structures are capable of producing enhanced optical fields under the illumination of some wavelengths residing in its surface plasmon resonance range. They have been used to improve the performance of quantum dot infrared photodetectors (QDIPs). Increased photocurrent and detection wavelength selection have been demonstrated.

The device structure of the GeSn p-i-n photodetector used for this research is shown in Figure (a). There are a set of three samples, all p-i-n photodiodes that were previously produced. Their measured dark I-V characteristics, and measured and simulated spectral response, are shown in Figures (b) through (d).

This work was done by Greg Sun of the University of Massachusetts for the Air Force Research Laboratory. AFRL-0249

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Silicon Based Mid-Infrared SiGeSn Heterostructure Emitters and Detectors (reference AFRL-0249) is currently available for download from the TSP library.

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