CAREER: Mixed-bonded IV-VI semiconductors for hybrid heterostructures

Stanford University, Stanford CA

Investigators

Abstract

The nature of bonding between the atoms that make up any material sets the ultimate properties of that material. This is true for structural materials used in construction with critical mechanical properties as well as for electronic materials used in computers, solar cells, and energy efficient lighting. The bonding in common electronic materials such as silicon, germanium, and III-V semiconductors has certain limitations in the infrared, a part of the light spectrum invisible to our eyes but that new sensors can use to examine objects around us in unprecedented ways. This project focuses on exploring a different class of electronic materials known as IV-VI semiconductors, which have very unusual bonding. The researchers would like to understand how the peculiar bonding of the IV-VIs can be harnessed for better infrared devices. Here, the research team is adopting a hybrid approach to combine the unique strengths of IV-VI materials without losing the practical advantages of common, established electronic materials. Along this theme, the team is building visual education tools, lab demonstrations, and public understanding videos all to highlight the nature of atomic bonding and demonstrate how a few simple rules at the atomic scale lead to complex structures. These activities engage with students at the high school, undergraduate, and graduate levels, guided by an inclusive approach to scientific education and training. Mixed covalent-ionic bonding in IV-VI semiconductors offers opportunity for advancing optoelectronics in the underserved mid-infrared and terahertz domains. These materials have ultra-narrow direct band gaps, with unusual carrier transport and recombination properties that are favorable for efficient integrated infrared light emitters. The research team is integrating IV-VI semiconductors with covalently bonded III-V materials via heteroepitaxy. This offers the chance to take the mature technology platform offered by III-V systems and boost it with new abilities from the IV-VI materials and their respective heterovalent interfaces. This project evaluates if such hybrid heterostructures may help overcome limitations in conventional infrared heterostructures by (1) modulating traditionally fixed interfacial electronic properties using tunable heterovalency, (2) screening and slowing down minority carriers from recombining at dislocation defects in integrated devices, and (3) providing new optical properties within heterostructures via stable and metastable polymorphs with inverted band structures. The research team uses molecular beam epitaxy to synthesize pristine IV-VI/III-V films and interfaces and analyzes their structure by transmission electron microscopy, x-ray diffractometry, atom probe tomography, and electron channeling contrast imaging. Electrical and optical measurements in the mid-infrared on larger devices as well as at the individual defect level provide insight into how synthesis and structure connect with the properties of interest. Bonding of matter and the search for new electronic materials form the core pillars of the research in this project. The research team integrates these two themes into an education and outreach program comprising of developing a cost-effective teaching tool to understand bonding in matter, science teacher training, workforce development via research, industry interaction, and curriculum development for this generation of post-silicon students. 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.