Nanoscale Design to Enable the Photon Management
Date Issued
2012
Date
2012
Author(s)
Hsu, Chia-Yang
Abstract
Nanostructures have shown great potential toward better performance than their bulk counterparts. However, every nanomaterials have their own limits, and thus future applications are being hindered. For making a breakthrough, in this study, we show a possible solution by combining two different nanomaterials together. By means of atomic layer deposition, the core-shell multiwalled carbon nanotubes (MCNTs)-TiO2/ZnO nanostructures could make the thickness control accurate. Duo to the potential applications of secure communication, a sensitive and fast photodetector (PD) is strongly desirable. However, the core-shell nanowires (NWs) not only converse the high photoconductive gain of the metal oxide semiconductor but also further promote the response speed. This material may pave a promising way for multifunctional NW-based optoelectronics in the future. In addition, a model concerning the connections between two materials is proposed to explain the high photoconductive gain and the fast response speed.
First of all, a broadband, fast, and sensitive PD is realized on the basis of MCNT-TiO2 core-shell NW geometry. The devices exhibit high photoconductive gain up to 104 and fast response/recovery times of 4.4/10.2 ms. Advances in the carrier separation occurred in the radial junction in core-shell architecture, the collection of charge could be enhanced. Herein, the interaction between MCNT and TiO2 is demonstrated by photocurrent generation and temporal behavior under varying wavelength illumination. The high photoconductive gain and fast response/recovery times are attributed to the presence of oxygen-related hole-trap states at the NW surface and the radial local electric field between MCNT cores and TiO2 shells duo to Schottky junctions. Furthermore, duo to the optoelectronic properties of core-shell NW, the material has great potential in photovoltaic cells applications.
Finally, for astronomical studies and optical communication, self-powered UV devices are much more desired. Herein, we employ the advantages of core-shell nanostructures to fabricate ultrafast, and self-powered ultraviolet (UV) PDs. Although the self-powered devices have been studied recently on the basis of NW-aligned arrays, little attention has paid on driving practical device by a single NW. We not only demonstrate sensitive MCNT-ZnO core-shell NW device with responsivity of 200 A/W and photoconductive gain of 800 under UV laser (325 nm, 100 mW/cm2) but also operate without an external power supply to continuously drive a commercial liquid crystal display. Furthermore, we show the first fast-speed demonstration of MCNT-ZnO-based PDs in vacuum condition with response/recovery times of 29/30 ms duo to the advantages of radial Schottky junctions and thin ZnO shells. We provide multifunctional coaxial nanostructures for the promising application in the future.
Subjects
Core-shell
Carbon nanotubes
Photodetector
Nanowire
Schottky
TiO2
ZnO
Self-powered
SDGs
Type
thesis
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