Date of Award

Spring 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering (ENAS)

First Advisor

Xia, Fengnian

Abstract

Thin-film layered and traditional materials exhibit distinctive physics properties from their bulk counterparts. Thin-film materials bridges the gap between monolayer two-dimensional (2D) materials and bulk materials and possess the advantages of both, e.g., large tunability and high stability. However, recent research efforts focus on physical properties of monolayer 2D materials while state-of-art commercialized device applications are dominated by conventional bulk materials. Therefore, great potentials remain unexplored in thin-film materials, which host novel physics phenomenon and are promising for advanced device applications. In this work, we investigated the fundamental light-mattering properties of the thin-film materials and further demonstrated thin film devices for optoelectronic applications. The light-matter interactions in thin-film materials exhibit many fascinating physical properties. We first report symmetry-controlled electron-phonon interactions in strong-coupled thin-film layered materials/silicon dioxide (SiO2) vdWs heterostructures. Two optically silent Raman modes in amorphous SiO2 are activated by coupling with electronic transitions in thin-film layered materials, where the chirality and anisotropy are controlled by intrinsic electronic band properties of layered materials. In addition, Raman modes in honeycomb lattice can acquire unique chirality due to its pseudoangular momentum (PAM). We discuss a reduced chirality of Raman G mode with increasing layer number of the honeycomb graphene and hBN, suggesting that the interlayer interaction can significantly influence the symmetry of lattice vibration. Finally, we report a novel valley-selective linear dichroism in thin-film Tin Sulfide (SnS) with orthorhombic lattice. We observe two photoluminescence (PL) peaks, arising from band-edge optical interband transitions from two inequivalent valleys in SnS. The PL emission from Γ-X (Y) valley is completely x (y)-polarized. Thin-film materials also exhibit great potential for mid-infrared light generation, modulation and detection applications. We first report the PL properties of thin-film black phosphorus (BP), whose brightness is comparable to that of an indium arsenide multiple quantum well (MQW) structure. Remarkably, with a moderate displacement field up to 0.48 V/nm, the PL emission from a ~20-layer BP flake is continuously tuned from 3.7 to 7.7 μm, spanning 4 µm in mid-infrared spectral range. Our work provides a comprehensive understanding of mid-infrared light emission properties of thin-film BP, suggesting its promising future in mid-infrared tunable light emitting and lasing applications. In addition, we demonstrate an ultrafast microbolometer for mid-infrared light detection based on ultrathin silicon nanomembrane. In this device, a small heat capacity of approximately 1.9×10^(-11) J⁄K is achieved, which allows for its operation at a speed of over 10 kHz, around 100 times faster than commercial bolometers. Moreover, a compact diabolo antenna is leveraged for efficient mid-infrared light absorption, enabling the downscaling of the active area size to 6.2 µm by 6.2 µm. Due to its CMOS compatible fabrication processes, our demonstration may lead to the future high-resolution and high-speed LWIR imaging solution.

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