Collaborative Research: Quantum Transport in Self-Assembled Hybrid Superlattices

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New phenomena emerge when two semiconductors are brought together in a periodic structure. Such semiconducting superlattices have properties not observed in bulk semiconductor crystals. Their unique properties have led to novel devices such as tunable optical filters, infrared photodetectors, and quantum cascade lasers. Superlattices are expensive to make, requiring ultrahigh vacuum and meticulous layer by layer assembly. The PIs aim to discover a new type of superlattice based on hybrid perovskites, materials with both organic and inorganic components. Hybrid perovskites can be solution processed, allowing for spontaneous assembly into layered nanostructures. Their chemical diversity can revolutionize superlattice research with a vastly expanded range of materials with varied properties. This research will enable future superlattice devices that are scalable and cost-effective. This project will also provide interdisciplinary training to undergraduate and graduate students, providing them with critical-thinking and problem-solving skills needed for CAREERs in STEM and industry.Semiconducting superlattices are quantum heterostructures important to condensed matter physics and with applications in advanced electronic technologies. The constituents of the superlattices to date have been limited to inorganic semiconductors, such as GaAs and AlGaAs. This project will investigate quantum transport in a new class of semiconducting superlattices based on Ruddlesden-Popper halide perovskites. The project will employ theoretical and experimental studies in an iterative manner so as to accelerate materials discovery. First principle density functional theory (DFT) calculations will be used to predict materials structures and the optical and electronic properties will be modeled by combining tight-binding models with the DFT calculations. Superlattice structures will be prepared by solution processing and self-assembly, allowing for facile tuning of the electronic structure by varying constituents. The design strategy, using semiconducting organic ligands, will create new possibilities for band engineering. Electrooptical measurements will be used to identify signatures of semiconducting superlattices such as electronic minibands. Complementary electrical characterization will be used to search for evidence of quantum transport, using optical excitation to generate charge carriers without unintended effects arising from doping. The project will elucidate the properties of 2D perovskite superlattices, differentiate their behaviors from conventional inorganic superlattices, and determine if their optical and electronic properties can be tailored in a controllable manner.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.