Advanced Optoelectronic Devices Based on Semiconducting Nanowires


Student thesis: Doctoral Thesis

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Awarding Institution
Award date25 Aug 2021


Due to the advent of nanotechnology, materials can be readily fabricated into nanoscale configurations with different dimensionalities and widely tunable properties for technological applications. In particular, one-dimensional (1D) semiconducting nanowires (NWs) were demonstrated with many exciting properties, which attract wide attention to their further development for many advanced optoelectronic technologies. To date, various NW technologies have shown many advantages in terms of charge carrier transport, energy efficiency, mechanical flexibility, process scalability, and device miniaturization that usually outperform other counterparts. In this dissertation, the successful synthesis of the crystalline semiconducting NWs, including inorganic perovskite halides, core-shell perovskites, superlattice oxides, is presented by using chemical vapor deposition method, and more importantly, their optoelectronic properties and applications have also been investigated.

First, the catalytic vapor-liquid-solid (VLS) growth of crystalline all-inorganic perovskite halides (CsPbX3; X = Cl, Br, or I) NWs is developed. Specifically, large-area vertical perovskite NW arrays with a uniform diameter of ~150 nm are successfully synthesized using Sn catalysts. To understand the VLS growth kinetics of these all-inorganic perovskite NWs, the effect of growth pressure, growth temperature, catalyst density, and growth rate on the NW growth are thoroughly investigated. With defect-free and single-crystalline features, these all-inorganic perovskite NWs devices exhibit excellent performance with high light-to-dark current ratio, large photoresponsivity, and decent mobility when configured into photodetectors and field-effect transistors. These results highlight the technological potency of these VLS-grown all-inorganic perovskite CsPbX3 NWs for high-performance (opto) electronic devices.

Furthermore, the realization of high-mobility cesium lead bromide perovskite (CsPbBr3) NW devices is reported via a simple surface charge transfer doping strategy. Based on the photoemission spectroscopy analysis, it is apparent that the CsPbBr3 NWs are strongly p-type doped by just depositing the molybdenum trioxide (MoO3) shell layer due to the interfacial electron transfer from CsPbBr3 NW core to MoO3 shell. After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs, together with a superior responsivity (R) up to 2.36×103 A/W and an external quantum efficiency (EQE) over 5.48×105 % towards photodetection in visible region. Significantly, this MoO3 shell passivation can effectively suppress the environmental degradation of perovskite core as revealed by detailed electron microscopy investigations; as a result, the excellent air stability of CsPbBr3/MoO3 core-shell NW FETs is achieved. Therefore, it is promising to employ surface charge transfer doping to improve both electrical performance and environmental stability of future nanostructured halide perovskite devices.

Finally, enabled by quasi-two-dimensional electron gases (quasi-2DEGs) in InGaO3(ZnO)3 superlattice NWs, an artificial visual system is built to mimic the human ones. This system is based on an unreported device concept combining coexistence of oxygen adsorption-desorption kinetics on NW surface as well as strong carrier quantum-confinement effects in superlattice core, to resemble the biological Ca2+ ion flux and neurotransmitter release dynamics. Given outstanding mobility and sensitivity of superlattice NWs, an ultralow energy consumption down to sub-femtojoule (fJ) per synaptic event is realized in quasi-2DEGs synapses, which rivals that of biological synapses and currently available synapse-inspired electronics. Notably, a flexible quasi-2DEGs artificial visual system is demonstrated to simultaneously perform high-performance light detection, brain-like information processing, non-volatile charge retention, in-situ multibit-level memory, orientation selectivity, and image memorizing.