Neuartige Photomischer mit eindimensionalen und zweidimensionalen Nanokontakten für den Terahertz-Bereich
Zusammenfassung der Projektergebnisse
The photoconductive based photomixers are very efficient THz sources. Optoelectronic generation of continuous-wave (CW) terahertz signals relies on mixing of two optical signals. High bandwidth will be obtained by frequency-tuning of one of the two lasers. However, a broadband efficient THz source operating at room-temperature remains a significant technical challenge for the development of a compact terahertz system. Conventional photomixers can partially fulfill such requirements and do often use an interdigital finger structure. The main drawbacks of this conventional CW THz photomixer are a large parasitic capacitance and a limited current capability of the electrodes. Typical device failure mechanisms have been recognized due to the electromigration, thermal failure, and high-field breakdown failures. The device capacitance and the antenna resistance result in an abrupt RC roll-off. In this project, metallic nanowire and multilayers graphene were successfully used as nanoelectrode to overcome the drawbacks and failure mechanisms of conventional CW THz photomixers. The most important findings and conclusions about the nanoelectrode CW THz photomixers can be summarized as follows: A. Lateral photomixers: A new photomixer structure consisting of a single nanowire (Ag-NW) over LTG-GaAs with a nanowire diameter of 120 nm and an electrode gap of ~1 μm has been fabricated. The main advantages of nanowire electrodes compared to interdigital (ID) electrodes are the small device capacitance with < 0.1 fF (a factor of more than 10) and the high photocurrent > 5 mA (a factor of more than 15). The optimized device showed higher THz power (about one order of magnitude) at around 1 THz frequency compared to our former reported results with NW photomixers. - A new CW THz photomixer based on semi-insulating GaAs (SI-GaAs) with Ag-NW was for the first time demonstrated. The THz output power was ~one order of magnitude higher at 0.2 THz compared to ID devices. This device compensated the large carrier lifetime of the SI-GaAs photoconductor. - The CVD-grown Trivial Transfer Graphene™ (TTG) with 6-8 layers were transferred onto LTG-GaAs substrates. The photocurrent of the 2D graphene photomixer is one order of magnitude higher than the photocurrent of conventional ID device due to the transparency of the graphene which allows most of the optical beat signal to propagate through the graphene and increase the number of the excited carriers. This leads to higher photocurrents and enhanced THz output power (a factor of more than 10) at around 0.8 THz compared to our former reported results with graphene photomixers. B. Vertical photomixers: A new type of a fully integrated vertical nanocontact THz photomixer was fabricated on LTG-GaAs / n+GaAs / SI-GaAs wafer with a single Ag-NW of ∅ 120 nm. The vertical structure compensates some drawbacks of lateral structures such as electric field spikes and an abrupt decrease of the electrical field as a function of the depth. It was clearly shown that the nanocontacts reduced the device capacitance by around one order of magnitude (from 6 to 0.6 fF) without reducing the photocurrent (~ 5 mA). - The antenna integration becomes less complex due to the full integration on a single wafer which improves the reliability and the overall performance of the photomixer. The new vertical NW device with a LTG-GaAs form the first wafer supplier showed compared to the conventional lateral photomixer with ID electrodes higher THz power by a factor of ~70 and 10 at 0.8 THz and 2.25 THz, respectively. An improved LTG-GaAs device from the second wafer supplier CNRS-IEMN in France showed an absolute THz power of more than 4 µW at 0.625 THz. The DC characteristics of all types of the nanoelectrode photomixers showed a large increase of the photocurrent of up to 20 and 32 times in lateral and vertical photomixers, respectively, compared to the photocurrent in the conventional lateral photomixer with ID electrodes. The THz measurement results of the Ag-NW contacted lateral and vertical photomixer clearly showed the benefits of the combination of very low capacitance and high photocurrent by higher THz output power generation and wider frequency range as compared to standard photomixers. The output power enhancement of both lateral and vertical Ag-NW devices is also partly due to the surface plasmon polaritons. The wave patterns of surface plasmon polaritons (SPPs) on the Ag-NW were obtained using a scattering-type scanning near-field optical microscope (s-SNOM). These new vertical and lateral photomixers have to be encapsulated for higher reliability. The integration with a two-tone laser or two VCSEL lasers will result in a compact broadband THz source for multiple new applications.
Projektbezogene Publikationen (Auswahl)
- “CW THz photomixers at 850 nm and 1550 nm using dielectrophoretic alignment of Ag-nanowire”. 41st IRMMW-THz - 2016, Copenhagen, Denmark; 09/2016
Mohammad Tanvir Haidar, Shihab Al-Daffaie, Oktay Yilmazoglu, Ahid S. Hajo, Franko Kueppers
(Siehe online unter https://doi.org/10.1109/IRMMW-THz.2016.7758754) - “Graphene-Nanowire Hybrid Photomixer for Continuous-Wave Terahertz Generation”. 42th IRMMW-THz 2017, Cancún, México; 08/2017
Alaa Jumaah, Shihab Al-Daffaie, Oktay Yilmazoglu, Franko Küppers
(Siehe online unter https://doi.org/10.1109/IRMMW-THz.2017.8067085) - First Demonstration of Continuous Wave Terahertz Radiation From Semi-Insulating GaAs Photomixer with Nanowire. 2018 43rd IRMMW-THz, Nagoya, Japan; 09/2018
Shihab Al-Daffaie, Oktay Yilmazoglu, Alaa Jabbar Jumaah Zangana, Franko Kueppers
(Siehe online unter https://doi.org/10.1109/IRMMW-THz.2018.8510294) - “Graphene Enhanced 2-D Nanoelectrode for Continuous Wave Terahertz Photomixers”. 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Nagoya, Japan; 09/2018
Alaa Jabbar Jumaah Zangana, Shihab Al-Daffaie, Oktay Yilmazoglu, Franko Kueppers
(Siehe online unter https://doi.org/10.1109/IRMMW-THz.2018.8510179) - "Experimental Investigation of Graphene Layers as 2D Nanoelectrode for Continuous Wave Terahertz Generation," 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2019, pp. 1-2
Alaa Jumaah, Shihab Al-Daffaie, Oktay Yilmazoglu, Franko Küppers, and Thomas Kusserow
(Siehe online unter https://doi.org/10.1109/IRMMW-THz.2019.8874024) - "Sliver Nanowire Surface Plasmon Polaritons enhancement in Terahertz Nanodevices," 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2019, pp. 1-2
Shihab Al-Daffaie, Oktay Yilmazoglu, Matthias M. Wiecha, Amin Soltani, Franko Küppers, Thomas Kusserow, and Hartmut G. Roskos
(Siehe online unter https://doi.org/10.1109/IRMMW-THz.2019.8874523) - “Interdigital Multilayer-Graphene Nanoelectrodes for Continuous Wave Terahertz photomixers”, EuMCE, May 2019, Prague Czech
Alaa Jumaah, Shihab Al-Daffaie, Oktay Yilmazoglu, Franko Küppers, and Thomas Kusserow
- “Interdigital Multilayer-Graphene Nanoelectrodes for Continuous Wave Terahertz photomixers”, EuMCE, May 2019, Prague Czech
Alaa Jumaah, Shihab Al-Daffaie, Oktay Yilmazoglu, Franko Küppers, and Thomas Kusserow
