FuSe-TG: Monolithic Heterointegration of GeSn and SiGeSn Alloys with Silicon Platforms

Arizona State University, Scottsdale AZ

Investigators

Abstract

PART I: NON-TECHNICAL SUMMARY This Future of Semiconductors (FuSe) project focuses on developing infrared light sensors based on alloys of silicon, germanium, and tin, all of which belong to the fourth group of the Periodic Table. These group-IV materials are chemically compatible, making it possible to integrate light detection and signal processing capabilities (the latter based on pure silicon) on a single, monolithic chip. By contrast, current infrared technology is mainly based on expensive materials that are incompatible with silicon and sometimes even toxic. The grant enables the formation of a team, which consists of investigators from three different universities, to pursue key scientific challenge for the integration of heterogeneous materials is accommodating the difference in size between the atomic blocks that make up their crystal structures. This size mismatch can induce atomic misplacements that degrade the performance of detector devices. The solution requires collaborative work between physicists, chemists, materials scientists, and device engineers. The multidisciplinary character of the team provides a unique educational experience for the future workforce by integrating many different perspectives around the co-design ideas of the FuSe program. The team members have a very diverse and complementary expertise, from circuit design to fully microscopic quantum-mechanical simulations, including the development of new synthetic strategies beyond conventional methods. PART II: TECHNICAL SUMMARY The team is building research collaborations aimed at overcoming the very large lattice mismatch between silicon and infrared GeSn or SiGeSn alloys (which exceeds 4% and limits the critical thickness for defect-free growth to one or two atomic monolayers) for monolithic integration of detectors and readout components, understanding the ultimate dark current limits of diodes based on GeSn or SiGeSn, and designing readout circuitry matched to these diode characteristics and to the growth of the infrared devices. Within these general research targets, the initial team-building effort is carried out with the purpose of determining the structure of misfit dislocations between GeSn alloys and Si substrates, performing detailed spectroscopy of point defects, understanding dislocations and point defects using first-principles calculations, and eliminating surface defects that contribute to the dark current. During the FuSe Teaming Grant period the team addresses these challenges using a multidisciplinary approach by fully characterizing the structural properties of the alloys and their interface with Si by performing Rutherford Backscattering, Raman, x-ray diffraction, atomic force microscopy, and electron microscopy studies. In particular, the latter makes it possible to determine the nature of the dislocations that control the strain-relaxation progress. The team also evaluates electrical and optical properties of novel passivating dielectrics, antireflection layers and oxides for GeSn or SiGeSn alloys, and the researchers perform systematic spectroscopy studies of defects that can be associated with observed dark currents in GeSn and SiGeSn diodes. These preliminary investigations along with large-scale first-principles theoretical simulations of the defected interfaces and point defects to interpret the observed structural and electrical properties of the alloy devices and the general team-forming activities lay the foundation for future focused, research-intense projects. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.