Browsing by Author "Lee, Ming-Hao"

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Large Photoresponsivity in the Amorphous-TiO2/SrRuO(3)Heterostructure
(1970-01-01)
Liu, Heng-Jui
;
Huang, Chin-Han
;
Chen, Cheng-Ying
;
Hsiao, Sheng-Wei
;
Chen, You-Sheng
Thin-film heterostructures are effective in enhancing the performance or triggering novel physical phenomena of optoelectronic applications. For example, the epitaxial heterostructures of ultraviolet-light-sensitive TiO(2)with metallic SrRuO(3)can acquire visible-light functionalities using the hot carrier injection mechanism. Therefore, the TiO2/SrRuO(3)heterostructure system has recently attracted increasing interest. Herein, the amorphous-TiO2/SrRuO(3)heterostructure is fabricated and compared to the epitaxial TiO2/SrRuO3. As opposed to the occurrence of the visible-light photovoltaic effect in the epitaxial TiO2/SrRuO3, the amorphous-TiO2/SrRuO(3)heterostructure herein exhibits different optoelectronic functionality, specifically the photoresistor behavior. The amorphous-TiO2/SrRuO(3)heterostructure achieves a photoresponsivity of 6.56 A W(-1)at 1 V. Such a performance is hardly obtained in typical oxide-based photoresistors. The analyses of the crystalline and electronic structures show that it is due to the defect-induced high electron doping in the amorphous TiO(2)with hot carrier injection mechanism. This study discusses the correlation between the hot carrier injection and band diagram, which provides more degrees of freedom in designing potential optoelectronic devices.
Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers
(2018-04-10)
Hsu, Wei-Ting
;
Lu, Li-Syuan
;
Wu, Po-Hsun
;
Lee, Ming-Hao
;
Chen, Peng-Jen
Van der Waals heterobilayers of transition metal dichalcogenides with spin-valley coupling of carriers in different layers have emerged as a new platform for exploring spin/valleytronic applications. The interlayer coupling was predicted to exhibit subtle changes with the interlayer atomic registry. Manually stacked heterobilayers, however, are incommensurate with the inevitable interlayer twist and/or lattice mismatch, where the properties associated with atomic registry are difficult to access by optical means. Here, we unveil the distinct polarization properties of valley-specific interlayer excitons using epitaxially grown, commensurate WSe2/MoSe2 heterobilayers with well-defined (AA and AB) atomic registry. We observe circularly polarized photoluminescence from interlayer excitons, but with a helicity opposite to the optical excitation. The negative circular polarization arises from the quantum interference imposed by interlayer atomic registry, giving rise to distinct polarization selection rules for interlayer excitons. Using selective excitation schemes, we demonstrate the optical addressability for interlayer excitons with different valley configurations and polarization helicities.
Tailoring excitonic states of van der Waals bilayers through stacking configuration, band alignment, and valley spin
(2019-12-01)
Hsu, Wei-Ting
;
Lin, Bo-Han
;
Lu, Li-Syuan
;
Lee, Ming-Hao
;
Chu, Ming-Wen
Excitons in monolayer semiconductors have a large optical transition dipole for strong coupling with light. Interlayer excitons in heterobilayers feature a large electric dipole that enables strong coupling with an electric field and exciton-exciton interaction at the cost of a small optical dipole. We demonstrate the ability to create a new class of excitons in hetero- and homobilayers that combines advantages of monolayer and interlayer excitons, i.e., featuring both large optical and electric dipoles. These excitons consist of an electron confined in an individual layer, and a hole extended in both layers, where the carrier-species-dependent layer hybridization can be controlled through rotational, translational, band offset, and valley-spin degrees of freedom. We observe different species of layer-hybridized valley excitons, which can be used for realizing strongly interacting polaritonic gases and optical quantum controls of bidirectional interlayer carrier transfer.