Browsing by Author "Sun, Hsu"

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Scalable MoS2/graphene hetero-structures grown epitaxially on sapphire substrates for phototransistor applications
(2018-02-01)
Chen, Hsuan-An
;
Chen, Wei-Chan
;
Sun, Hsu
;
Lin, Chien-Chung
;
Lin, Shih-Yen
Bi-layer graphene is grown directly on sapphire substrates by using ethane as the precursor without the assistance of a metal catalyst. A growth model of graphene flake formation in the furnace, followed by a complete film growth is also proposed. Using the graphene/sapphire sample as the new substrate, scalable MoS2 films with good layer number controllability can be grown directly on the substrate. After fabricating the MoS2/graphene hetero-structures into bottom-gate photo-transistors, a Dirac point shift is observed for the device under the light irradiation condition, which is attributed to the extraction of photo-excited electrons in the MoS2 layer to the graphene channel. The photo-voltaic response observed for the photo-transistors may provide a potential application of the 2D material hetero-structure in thin-film solar cells.
Single-Crystal Antimonene Films Prepared by Molecular Beam Epitaxy: Selective Growth and Contact Resistance Reduction of the 2D Material Heterostructure
(2018-05-02)
Chen, Hsuan-An
;
Sun, Hsu
;
Wu, Chong-Rong
;
Wang, Yu-Xuan
;
Lee, Po-Hsiang
Single-crystal antimonene flakes are observed on sapphire substrates after the postgrowth annealing procedure of amorphous antimony (Sb) droplets prepared by using molecular beam epitaxy at room temperature. The large wetting angles of the antimonene flakes to the sapphire substrate suggest that an alternate substrate should be adopted to obtain a continuous antimonene film. By using a bilayer MoS2/sapphire sample as the new substrate, a continuous and single-crystal antimonene film is obtained at a low growth temperature of 200 degrees C. The results are consistent with the theoretical prediction of the lower interface energy between antimonene and MoS2. The different interface energies of antimonene between sapphire and MoS2 surfaces lead to the selective growth of antimonene only atop MoS2 surfaces on a prepatterned MoS2/sapphire substrate. With similar sheet resistance to graphene, it is possible to use antimonene as the contact metal of 2D material devices. Compared with Au/Ti electrodes, a specific contact resistance reduction up to 3 orders of magnitude is observed by using the multilayer antimonene as the contact metal to MoS2. The lower contact resistance, the lower growth temperature, and the preferential growth to other 2D materials have made antimonene a promising candidate as the contact metal for 2D material devices.