Abstract
Large-area electronics involves devices, circuits, and systems that can be integrated onto various substrates, including silicon wafers, glass, and flexible substrates. The array fabrication of devices via vapor deposition techniques enables device densities ranging from 5 to over 3000 devices per inch, facilitating applications from pressure sensing to enhanced vision in augmented reality. In addition to extensively studied high-performance materials, such as hydrogenated amorphous silicon, metal oxide semiconductors, transition metal dichalcogenides (TMDs), and organic semiconductors, nonmetallic chalcogen compounds and main group elements exhibit unique electrical properties, thermoelectric performance, and band structures. Investigating their physical properties may expand their potential for further advancement of optoelectronics and other emerging electronics. In this dissertation, a high-vacuum vapor deposition technique, compatible with modern semiconductor manufacturing processes, was employed to fabricate scalable Bi2Se3 thin films. Additionally, a pulsed irradiation synthesis (PIS) method was developed to achieve low-temperature crystallization of compound thin films, making this post-deposition processing technique applicable to various compound thin films and thermally unstable substrates. Leveraging the excellent thermoelectric properties of Bi2Se3, thermal coupling between the material and the substrate was utilized to enable photothermoelectric detection from visible to near-infrared wavelengths. Moreover, by introducing oxygen during deposition, a disordered tellurium oxide thin film was synthesized. The adsorption and desorption of gases on the disordered surface structure were explored, enabling the controllable modulation of channel electrical properties under ambient conditions. This molecular-level modification of the channel material allowed for the reconfiguration between logic devices and optoelectronic neuromorphic devices.To begin, a stacked film was obtained by alternative evaporation of elemental Bi and Se to fabricate Bi2Se3 thin films. Using PIS, the crystallization temperature was significantly reduced, reaching as low as 150°C. The photoresponse of Bi2Se3 photodetectors on polyimide (PI) substrates exhibited a broad spectral response from visible to near-infrared (1550 nm), unrestricted by the material's bandgap. This phenomenon was attributed to the photothermoelectric properties of the thin film. The device demonstrated an excellent responsivity of 71.9 V W⁻¹ at 1550 nm illumination and a fast response time of less than 50 ms. Based on the photothermoelectric detection mechanism, a position-dependent optoelectronic response was proposed.
Furthermore, we investigated the underlying mechanism behind the low-temperature crystallization enabled by this rapid synthesis process. The results indicated that the ultrafast low-temperature synthesis arose from a self-sustaining exothermic reaction triggered by high-temperature pulses. Moreover, Bi2Se3 films could be synthesized not only on PI but also on various thermally unstable substrates, including polyethylene terephthalate (PET), poly(ethylene 2,6-naphthalate) (PEN), and polydimethylsiloxane (PDMS). We further explore the impact of thermal coupling between Bi2Se3 and organic polymer substrates on the photothermoelectric signal and propose a thermal management strategy to enhance optoelectronic performance. In addition to Bi2Se3 thin films, other thermoelectric thin films, such as Bi2Te3 and SnSe2, are successfully fabricated, all exhibiting significant photoresponse under near-infrared illumination, demonstrating the compatibility of our low-temperature synthesis strategy with flexible electronics.
Finally, tellurium-based nonmetallic oxides and their applications in multifunctional devices were investigated. By incorporating oxygen into tellurium, which effectively retards the spontaneous crystallization of Te, a disordered tellurium oxide thin film is synthesized. First-principles simulations confirm that the disordered atomic structure on the surface strongly interacts with gas molecules in the air, inducing carrier modulation in the material. In vacuum, the device exhibits intrinsic p-type transport characteristics with a field-effect hole mobility of 10.02 cm2 V-1 s-1. Under ambient conditions, the interaction between gas molecules and the interface, combined with the photoinduced desorption effect through ultraviolet illumination, enabled effective modulation of channel conductivity, mimicking the behavior of optical neurons. Based on this mechanism, an artificial vision network capable of identifying invisible UV patterns in both static and dynamic environments was developed. It successfully simulated the bee vision, which denoted promising applications in biorealistic artificial vision systems.
| Date of Award | 24 Jun 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Johnny Chung Yin HO (Supervisor) |