EAGER: Lattice-matched direct-bandgap III-V photodetector materials to silicon

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Part 1:The electronic integrated circuit, built primarily of crystals of silicon, has transformed the way humans compute and exchange information. This progress been enabled by the development of ever more powerful manufacturing techniques for electronic integrated circuits. This manufacturing infrastructure has also enabled tremendous advances in other areas, such as solar cells and digital cameras, where silicon is used to turn incident light into electrical energy/current. However, the range of colors of light to which silicon is sensitive, as well as the speed with which it can detect light, are fundamentally limited. Here, we seek to study a new family of materials that offers the potential for sensing colors of light in the infrared to which silicon is not sensitive, as well as greatly increased speed of detection, with applications including autonomous vehicles, communication systems, and biomedical instrumentation. The key advantage is that these new materials share a compatible crystal structure with silicon, potentially allowing them to be grown as crystals directly on silicon and take advantage of the sophisticated silicon manufacturing infrastructure. The goal of this project is to answer key questions related to the potential to enhance light detection on silicon. This project will provide cutting-edge research opportunities for two Ph.D. students, increase research opportunities for undergraduates from historically underrepresented groups, and engage pre-K to 12 students with the exciting world of nanoscience.Part 2:Current approaches towards monolithic integration of direct bandgap materials on silicon suffer from a variety of challenges and there is no clear path to the lattice-matched materials needed to address important emerging applications in the near- and mid-infrared. For photodetectors specifically, lattice-matching is critical to avoid the excessive dark currents that plague metamorphic approaches. While silicon itself can be an extremely efficient photodetector, it is limited in spectral coverage to less than ~1.1 micron and the thick absorbing regions required for high quantum efficiency tend to limit achievable bandwidths to less than ~2 GHz. This project will focus on the potential for BGaAs and BGaInAs photodetectors, which could span ~1-5 micron cutoff wavelengths on silicon and offer dramatic bandwidth advantages due to their direct bandgap. It is underpinned by (1) the PI??s recent success incorporating record high boron contents up to ~22% into GaAs, nearly sufficient to lattice-match with silicon, (2) preliminary metal-semiconductor-metal BGaAs photodetectors, (3) successful initial growths of direct bandgap BGaAs on GaP, and (4) the commercial availability of GaP-on-Si substrates. This project will answer key questions that govern the potential viability of these emerging materials for photodetectors related to p- and n-doping, defect mitigation, and fundamental optical properties. Additionally, lattice-matching of BGaAs onto GaP-on-Si templates will be demonstrated for the first time, along with alloying with indium to produce tunable-bandgap BGaInAs alloys lattice-matched to silicon. While the focus here will be on addressing the requirements for direct bandgap lattice-matched photodetectors, it is important to note that much of these research findings could be applicable to emitters as well.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.