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Title

Nanoscale Optoelectronic Materials through Theoretical Modeling

Author/Speaker

Helios Y. Li, Nicholas X. Fang Department of Mechanical Engineering, The University of Hong Kong; HK Institute of Quantum Science & Technology, The University of Hong Kong

Abstract

Light-matter interaction, as the origin of optoelectronics and further nanoscale materials and devices, has earned huge research interests. Given the difficulties in producing perfect defect-free samples in nanoscale, theoretical methods exhibit superiorities in predicting and explaining physical phenomena in this field. Here, we picked two examples to demonstrate how theoretical methods such as density function theory (DFT) benefit the analysis and promotion of optoelectronics development. In the optoelectronic device aspect, 4H-SiC devices demonstrate substantial promise in high power electronics with the wide bandgap and excellent thermal conduction performance of 4H-SiC, but further application was limited by the strong surface states. Experimental results showed the possibility that ALD ZnO decoration alleviated surface states of 4H-SiC. Based on experiments, deeper explanations and evidence were provided by our DFT modeling and theoretical models, showing the manipulation of surface work function and polarity, and the utilization of Fermi level pinning effect, by surface decoration. In addition, the close looks at electron distribution, band structure, and structural properties consolidated our guesses and provided more information to explore the capabilities of this structure for advanced applications of devices. Numerical prediction of light response offered deeper physical aspects to device design and technology. Twisted bilayer graphene showed exceptional potential in converting traditional circuits to a new regime of 2D materials-based electronics and 3D circuits. This mainly comes from the remarkable electrical properties of graphene and the introduced symmetry by the additional atomic layer. Theoretical computations were done on revisiting the structural parameters of twisting bilayer graphene with large twisting angles, following the careful check of van der Waals interaction correction in DFT. The dielectric response of twisted bilayer graphene was visited to provide a more general picture of how it interacts with incident light. Results showed that the additional atomic layer and the varying twisting angle posed inevitable influences on van der Waals interlayer distance, and then phase differences of reflected light. The two examples of nanoscale optoelectronic materials demonstrate how theoretical modeling boosts the advance of optoelectronics performance and efficiency.