Browsing by Author "Shih, Chih-Kang"

Now showing 1 - 12 of 12

All-Color Plasmonic Nanolasers with Ultralow Thresholds
(2013)
Lu, Yu-Jung
;
Kim, Jisun
;
Chen, Hung-Ying
;
Chang, Wen-Hao
;
Shih, Chih-Kang
Diffraction-unlimited semiconductor nanolasers are demonstrated by using single shape-controlled InGaN/GaN core-shell nanorods as laser gain media on Ag films epitaxially grown on Si substrates. The use of atomically smooth Ag films allows us to fabricate low-loss plasmonic cavities for ultralow-threshold, continuous-wave (CW) nanolaser operation above liquid nitrogen temperature. Furthermore, the tunable band-gap energy of the InxGa1-xN alloy makes it possible to realize laser emission in the full visible spectrum.
All-Color Plasmonic Nanolasers with Ultralow Thresholds: Autotuning Mechanism for Single-Mode Lasing
(2014-08-01)
Lu, Yu-Jung
;
Wang, Chun-Yuan
;
Kim, Jisun
;
Chen, Hung-Ying
;
Lu, Ming-Yen
We report on the first demonstration of broadband tunable, single-mode plasmonic nanolasers (spasers) emitting in the full visible spectrum. These nanolasers are based on a single metal oxide semiconductor nanostructure platform comprising of InGaN/GaN semiconductor nanorods supported on an Al2O3-capped epitaxial Ag film. In particular, all-color lasing in subdiffraction plasmonic resonators is achieved via a novel mechanism based on a property of weak size dependence inherent in spasers. Moreover, we have successfully reduced the continuous-wave (CW) lasing thresholds to ultrasmall values for all three primary colors and have clearly demonstrated the possibility of "thresholdless" lasing for the blue plasmonic nanolaser.
All-Color Plasmonic Nanolasers with Ultralow Thresholds: Autotuning Mechanism for Single-Mode Lasing
(2014-08-01)
Lu, Yu-Jung
;
Wang, Chun-Yuan
;
Kim, Jisun
;
Chen, Hung-Ying
;
Lu, Ming-Yen
We report on the first demonstration of broadband tunable, single-mode plasmonic nanolasers (spasers) emitting in the full visible spectrum. These nanolasers are based on a single metal oxide semiconductor nanostructure platform comprising of InGaN/GaN semiconductor nanorods supported on an Al2O3-capped epitaxial Ag film. In particular, all-color lasing in subdiffraction plasmonic resonators is achieved via a novel mechanism based on a property of weak size dependence inherent in spasers. Moreover, we have successfully reduced the continuous-wave (CW) lasing thresholds to ultrasmall values for all three primary colors and have clearly demonstrated the possibility of "thresholdless" lasing for the blue plasmonic nanolaser.
Dielectric impact on exciton binding energy and quasiparticle bandgap in monolayer WS2 and WSe2
(2019-04-01)
Hsu, Wei-Ting
;
Quan, Jiamin
;
Wang, Chun-Yuan
;
Lu, Li-Syuan
;
Campbell, Marshall
Excitons, bound electron-hole pairs in a 2D plane, dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). A large exciton binding energy on the order of 0.5 eV was theoretically predicted and experimentally determined recently. These ultrastable excitons thus open an avenue to explore the exciton physics such as Bose-Einstein condensation and superfluidity at room temperature (Kasprzak et al 2006 Nature 443 409; Plumhof et al 2014 Nat. Mater. 13 247; Fogler et al 2014 Nat. Commun. 5 4555; Jiang and John 2014 Sci. Rep. 4 7432). Recent experiments further demonstrated the concept of Coulomb engineering via dielectric environments based on either solutions or few-layer graphene. However, the conducting nature of these dielectrics can lead to quenching of optical transitions. Thus, in order to utilize 'dielectric tuning' of the exciton binding energy and quasiparticle band gaps, one must use insulating dielectrics. Here, we investigate the impact of insulating dielectric environments on the exciton binding energy of monolayer WS2 and WSe2 by exciton Rydberg spectroscopy, in which the dielectric environment is systematically varied from kappa= 1.49 to 3.82. We found that, with increasing kappa value, the exciton binding energy and quasiparticle bandgap exhibit significant reductions. Quantitatively, our result follows the prediction of nonlocally-screened Keldysh potential very well. The fitted 2D polarizability, Chi(2D), agrees rather well with previous density function theory calculations. Their close agreement validates the nonlocally-screened Keldysh model which can be used to quantitatively predict the exciton binding energy for monolayer TMDs (and possibly other 2D materials) in different dielectric environments. Such a predictive model will play an important role for the design of van der Waals heterostructures and TMD-based optoelectronic devices.
Diffraction-Unlimited Plasmonic Nanolaser
(2015-01-01)
Lu, Yu-Jung
;
Kim, Jisun
;
Chen, Hung-Ying
;
Wu, Chihhui
;
Dabidian, Nima
Epitaxial Growth of Optically Thick, Single Crystalline Silver Films for Plasmonics
(2019-01-23)
Cheng, Fei
;
Lee, Chien-Ju
;
Choi, Junho
;
Wang, Chun-Yuan
;
Zhan, Qiang
Single crystalline Ag films on dielectric substrates have received tremendous attention recently due to their technological potentials as low loss plasmonic materials. Two different growth approaches have been used to produce single crystalline Ag films previously. One approach is based on repetitive cycles of a two-step process (low temperature deposition followed by RT annealing) using molecular beam epitaxy (MBE), which is extremely time-consuming due to the need for repeat growth cycles. Another approach is based on rapid e-beam deposition which is capable of growing thick single crystalline Ag films (>300 nm) but lacks the precision in thickness control of thin epitaxial films. Here, we report a universal approach to grow atomically smooth epitaxial Ag films by eliminating the repetitive cycles used in the previous two-step MBE method while maintaining the precise thickness control from a few monolayers to the optically thick regime, thus overcoming the limitations of the two aforementioned methods. In addition, we develop an in situ growth of aluminum oxide as the capping layer to protect the epitaxial Ag films. The quality of the epitaxial Ag films was evaluated using a variety of techniques, and the superior optical performance of the films is demonstrated by measuring the propagation length of surface plasmon polaritons (similar to 80 mu m at 632 nm) as well as their capability to support a plasmonic nanolaser in infrared incorporating an InGaAsP quantum well as the gain media.
Low-Threshold Plasmonic Lasers on a Single-Crystalline Epitaxial Silver Platform at Telecom Wavelength
(2017-06-01)
Lee, Chien-Ju
;
Yeh, Han
;
Cheng, Fei
;
Su, Ping-Hsiang
;
Her, Tsing-Hua
We report on the first demonstration of metal insulator semiconductor-type plasmonic lasers at the telecom wavelength (similar to 1.3 mu m) using top-down fabricated semiconductor waveguides on single-crystalline metallic platforms formed using epitaxially grown Ag films. The critical role of the Ag film thickness in sustaining. plasmonic lasing at the telecom wavelength is investigated systematically. Low-threshold (0.2 MW/cm(2)) and continuous-wave operation of plasmonic lasing at cryogenic temperatures can be achieved on a 150 nm Ag platform with minimum radiation leakage into the substrate. Plasmonic lasing occurs preferentially through higher-order surface-plasmon-polariton modes, which exhibit a higher mode confinement factor, lower propagation loss, and better field gain coupling. We observed plasmonic lasing up to 200 K under pulsed excitations. The plasmonic lasers on large-area epitaxial Ag films open up a scalable platform for on-chip integrations of plasmonics and optoelectronics at the telecom wavelength.
Monolayer Semiconductor Surface-Emitting Lasers Using 2D Dark Plasmonic Cavities
(2018-01-01)
Wang, Chun-Yuan
;
Shi, Jinwei
;
Raja, Soniya S.
;
Chen, Chun-An
;
Zhang, Xin-Quan
We demonstrated a low-threshold lasing from a monolayer gain medium which is made possible due to 2D feedback mechanism via strong exciton-SPP coupling in both real space and a wide range of momentum space.
Nanolasers Employing Epitaxial Plasmonic Layers
(2013-01-01)
Lu, Yu-Jung
;
Kim, Jisun
;
Chen, Hung-Ying
;
Wu, Chihhui
;
Sanders, Charlotte E.
Plasmonic Nanolaser Using Epitaxially Grown Silver Film
(1970-01-01)
Lu, Yu-Jung
;
Kim, Jisun
;
Chen, Hung-Ying
;
Wu, Chihhui
;
Dabidian, Nima
"A nanolaser is a key component for on-chip optical communications and computing systems. Here, we report on the low-threshold, continuous-wave operation of a subdiffraction nanolaser based on surface plasmon amplification by stimulated emission of radiation. The plasmonic nanocavity is formed between an atomically smooth epitaxial silver film and a single optically pumped nanorod consisting of an epitaxial gallium nitride shell and an indium gallium nitride core acting as gain medium. The atomic smoothness of the metallic film is crucial for reducing the modal volume and plasmonic losses. Bimodal lasing with similar pumping thresholds was experimentally observed, and polarization properties of the two modes were used to unambiguously identify them with theoretically predicted modes. The all-epitaxial approach opens a scalable platform for low-loss, active nanoplasmonics."
Plasmonic Nanolaser Using Epitaxially Grown Silver Film
(2012-01-01)
Lu, Yu-Jung
;
Kim, Jisun
;
Chen, Hung-Ying
;
Wu, Chihhui
;
Dabidian, Nima
Successful development of epitaxial Ag as a new plasmonic platform has enabled low-threshold, continuous-wave (CW) operation of a SPASER-enabled nanolaser comprised of a subdiffraction plasmonic cavity and a single InGaN@GaN core-shell nanorod gain medium.
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.