Study of spin photocurrent in 2D hybrid organic-inorganic perovskite multiple quantum wells

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Non-technical Abstract:Hybrid metal halide perovskites have emerged as a promising class of semiconductors with device applications in solar cells, light emitting diodes and transistors. These materials also have large spin-orbit coupling, which makes these perovskites a candidate for spintronic devices. Spintronics combines electronics with spin, an intrinsic property of elementary particles, to enable novel technologies such as energy efficient devices for data storage or advanced computing. Spintronic devices based on quantum wells made by alternating layers of inorganic semiconductors such as silicon or germanium are expensive to make by epitaxial growth. In contrast, a two-dimensional hybrid perovskite with a natural quantum well structure consisting of alternating organic and inorganic layers can be fabricated via low-cost, facile solution processing. Although perovskites meet several important prerequisites for viable spintronic devices, there is lack of fundamental understanding of the spin-related phenomena in this new type of quantum well. In this project, the research team will optically probe and manipulate spins in hybrid perovskite quantum wells. The project will yield a fundamental understanding of spin degree of freedom in these materials. This knowledge will help to develop guidelines for material synthesis and device engineering for efficient and cost-effective spintronic devices. Graduate and undergraduate students, particularly those from underrepresented groups, will participate in multi-level research activities. The general public will be involved through scientific exhibitions such as ‘EXPO Physics’ for middle and high school students and ‘Show-n-tell in Physics’ for elementary school students.Technical AbstractTwo-dimensional hybrid organic inorganic perovskites (2D-HOIPs) with a Ruddlesten-Popper layered structure have recently started transforming new fields. These materials have strong spin-orbit coupling, high-charge mobility, and an intrinsic quantum well structures with many interfaces and facile solution processability. Giant Rashba splitting was experimentally confirmed in these materials, highlighting their potential for cost-effective room temperature spintronic devices. However, a few key questions remain that need to be answered to clear the pathway to viable devices. The central question is how spin photocurrent is generated and manipulated in two-dimensional HOIP multiple quantum well. The goal of the project is to deepen the fundamental understanding of this new type of multiple quantum well by conducting a comprehensive study on spin photocurrent dependence on quantum well structure, crystal symmetry and imperfection. The quantum well structure in a HOIP can be easily tuned from pure two dimensional to quasi three dimensional by varying the number of inorganic layers. Hypothetically, the roles of excitons (dominant in two dimension) and free carriers (dominant in three dimension) will shift. The focus of this proposal is to characterize the difference of spin photocurrent behaviors in ‘excitonic’ and ‘free carrier’ quantum wells using photogalvanic spectroscopy. The objectives of the study are to measure spin photocurrent for free carriers and extract the information about Rashba/Dresselhaus effects, investigate the origin of spin-polarized current from excitons, and characterize the spin polarization of free and bound excitons through photogalvanic spectroscopy. The knowledge gained from this project is expected to complement the spin-photophysics well studied in two-dimensional electron gas quantum wells, and be informative to scientists working in optoelectronic and spintronics applications.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.