Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A53: Invited Session: Optoelectronic Response of Low Dimensional Materials |
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Sponsoring Units: DCMP Chair: Nathaniel Gabor, University of California, Riverside Room: Grand Ballroom C3 |
Monday, March 2, 2015 8:00AM - 8:36AM |
A53.00001: Electrical control and detection of nanoscale optical fields with 2d materials Invited Speaker: Frank Koppens |
Monday, March 2, 2015 8:36AM - 9:12AM |
A53.00002: Hot Carriers and Photoresponse in Graphene Invited Speaker: Qiong Ma The photoresponse of materials, which determines the performance of optoelectronic devices, is governed by energy relaxation pathways of photo-excited electron-hole pairs. In graphene, with the electron-lattice coupling strongly quenched by the vanishing electronic density of states, a novel transport regime is reached in which the photo-generated carrier population can remain hot while the lattice stays cool. In this talk, I will first show that light is converted to electrical currents in graphene p-n junctions through the hot-carrier assisted thermoelectric effect [1]. The relaxation processes are subsequently examined by photocurrent measurements at different lattice temperatures, in which we observe a non-monotonic temperature dependence that can be understood as resulting from the competition between two hot electron cooling pathways: momentum-conserving normal collisions that dominate at low temperatures and disorder-assisted supercollisions that dominate at high temperatures [2]. The peak temperature depends on carrier density and disorder concentration, thus allowing for an unprecedented way of controlling graphene's photoresponse. I will also show our observations of giant long-range photocurrent response in high-quality graphene transistor devices, which peaks at the charge neutrality point and exhibits highly ordered anti-symmetric spatial patterns with alternating photocurrent signs as a function of laser position. These patterns are strongly sensitive to device size and quality and occur in the absence of internal electrostatic or material interfaces, which may be related to the symmetry breaking on sample boundaries assisted by long-range hot carrier propagation [3]. \textbf{[1]} N. Gabor, J. Song, Q. Ma, N. Nair, T. Taychatanapat, K. Watanabe, T. Taniguchi, L. Levitov and P. Jarillo-Herrero, Hot carrier--assisted intrinsic photoresponse in graphene, Science \textbf{334}, 648 (2011). \textbf{[2]} Q. Ma, N. Gabor, T. Andersen, N. Nair, K. Watanabe, T. Taniguchi and P. Jarillo-Herrero, Competing channels for hot-electron cooling in graphene, Phys. Rev. Lett$.$ \textbf{112}, 247401 (2014). \textbf{[3]} Q. Ma, N. Gabor et al., Giant long-range photocurrent patterns near the charge neutrality point in graphene, in preparation. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:48AM |
A53.00003: Optoelectronics with 2D semiconductors Invited Speaker: Thomas Mueller Two-dimensional (2D) atomic crystals, such as graphene and layered transition-metal dichalcogenides, are currently receiving a lot of attention for applications in electronics and optoelectronics. In this talk, I will review our research activities on electrically driven light emission, photovoltaic energy conversion and photodetection in 2D semiconductors. In particular, WSe2 monolayer p-n junctions formed by electrostatic doping using a pair of split gate electrodes, type-II heterojunctions based on MoS2/WSe2 and MoS2/phosphorene van der Waals stacks, 2D multi-junction solar cells, and 3D/2D semiconductor interfaces will be presented. Upon optical illumination, conversion of light into electrical energy occurs in these devices. If an electrical current is driven, efficient electroluminescence is obtained. I will present measurements of the electrical characteristics, the optical properties, and the gate voltage dependence of the device response. In the second part of my talk, I will discuss photoconductivity studies of MoS2 field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photoconductive gain. A model will be presented that reproduces our experimental findings, such as the dependence on optical power and gate voltage. We envision that the efficient photon conversion and light emission, combined with the advantages of 2D semiconductors, such as flexibility, high mechanical stability and low costs of production, could lead to new optoelectronic technologies. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:24AM |
A53.00004: Single carbon-nanotube photonics and optoelectronics Invited Speaker: Yuichiro K. Kato Single-walled carbon nanotubes have unique optical properties as a result of their one-dimensional structure. Not only do they exhibit strong polarization for both absorption and emission, large exciton binding energies allow for room-temperature excitonic luminescence. Furthermore, their emission is in the telecom-wavelengths and they can be directly synthesized on silicon substrates, providing new opportunities for nanoscale photonics and optoelectronics. Here we discuss the use of individual single-walled carbon nanotubes for generation, manipulation, and detection of light on a chip. Their emission properties can be controlled by coupling to silicon photonic structures such as photonic crystal microcavities [1] and microdisk resonators [2]. Simultaneous photoluminescence and photocurrent measurements show that excitons can dissociate spontaneously [3], enabling photodetection at low bias voltages despite the large binding energies. More recently, we have found that alternating gate-voltages can generate optical pulse trains from individual nanotubes [4]. Ultimately, these results may be combined to achieve further control over photons at the nanoscale. \\[4pt] [1] R. Miura, S. Imamura, R. Ohta, A. Ishii, X. Liu, T. Shimada, S. Iwamoto, Y. Arakawa, and Y. K. Kato, Nature Commun. 5, 5580 (2014). \\[0pt] [2] S. Imamura, R. Watahiki, R. Miura, T. Shimada, and Y. K. Kato, Appl. Phys. Lett. 102, 161102 (2013). \\[0pt] [3] Y. Kumamoto, M. Yoshida, A. Ishii, A. Yokoyama, T. Shimada, and Y. K. Kato, Phys. Rev. Lett., 112, 117401 (2014). \\[0pt] [4] M. Jiang, Y. Kumamoto, A. Ishii, M. Yoshida, T. Shimada, and Y. K. Kato, arXiv:1407.7086. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 11:00AM |
A53.00005: Many-body interactions in atomically thin 2D materials Invited Speaker: Alexey Chernikov Since the discovery of graphene, a single sheet of carbon atoms, research focused on two-dimensional (2D) materials evolved rapidly due the availability of atomically thin, thermally stable, high-quality crystals with intriguing physical properties. The 2D materials naturally inherit major traits associated with systems of reduced dimensionality: strongly enhanced Coulomb interactions, efficient light-matter coupling, and sensitivity to the environment. In particular, the considerable strength of the Coulomb coupling between the charge carriers introduces a rich variety of many-body phenomena. In the class of 2D semiconductors, e.g., this leads to the emergence of strongly bound electron-hole quasi-particles, such as excitons, trions, and biexcitons, with unusually high binding energies and efficient light absorption. In this talk, I will present a study of the excitonic properties of 2D semiconductors, as exemplified in recent works on atomically thin transition metal dichalcogenides [1-4]. The observation of exciton binding energies on the order of 0.5 eV and the marked deviation of the exciton Rydberg series from the hydrogenic model will be discussed. The results reflect both strong carrier confinement and the distinctive nature of dielectric screening in atomically thin materials. I will further describe how carrier doping and strong photo-excitation can profoundly alter the many-body interactions in these 2D systems. \\[4pt] [1] A. Chernikov, T. C. Berkelbach, H. M. Hill, A. Rigosi, Y. Li, O. B. Aslan, D. R. Reichman, M. S. Hybertsen, and T. F. Heinz, Phys. Rev. Lett. 113, 076802 (2014). \\[0pt] [2] K. He, N. Kumar, L. Zhao, Z. Wang, K. F. Mak, H. Zhao, and J. Shan, Phys. Rev. Lett. 113, 026803 (2014). \\[0pt] [3] Z. Ye, T. Cao, K. O'Brien, H. Zhu, X. Yin, Y. Wang, S. G. Louie, and X. Zhang, Nature 513, 214 (2014). \\[0pt] [4] M. M. Ugeda, A. J. Bradley, S. Shi, F. H. da Jornada, Y. Zhang, D. Y. Qiu, W. Ruan, S. Mo, Z. Hussain, Z. Shen, F. Wang, S. G. Louie, and M. F. Crommie, Nat. Mater. 1 (2014). [Preview Abstract] |
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