2014 Fiscal Year Research-status Report
Graphene terahertz detectors based on plasmons and resonant tunneling
| Project/Area Number |
26820123
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| Research Institution | Tohoku University |
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Principal Investigator |
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| Project Period (FY) |
2014-04-01 – 2016-03-31
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| Keywords | terahertz / graphene / detectors / sources |
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| Outline of Annual Research Achievements |
During this first year design and fabrication of 4 devices were carried out. The fabricated devices structure consist of a double graphene layer (DGL) heterostrucrture independently contacted with side contacts and having active area dimensions of 1.5 x 36.4 um^2, 1.5 x 48 um^2 , 800 x 830 nm^2 and 760 x 690 nm^2 respectively. The two graphene Layers (GLs) of the structure are separated by a thin transparent boron nitride tunnel-barrier layer with thickness of 3 nm, 2.3 nm 1.6 nm and 2 nm respectively.
Right after we conducted terahertz (THz) photo-emission and detection measurements on the first 2 devices. For detection experiments we used a CW THz source, based on a photoconductive photomixer switch, which delivers tunable THz beam up to 1 THz. We successfully measured the tunneling current induced by the incoming THz beam at 300 K. The detection experiments were done in an oblique incidence configuration to maximize the THz electric field perpendicular to the GLs and thus the resonant tunneling transitions associate with the absorption of the THz photon. For emission experiments we used a fourier transform far-infrared spectrometer to observe the spontaneous emissions associated with the photon assisted resonant tunneling transitions.
Therefore design and fabrication of DGL heterostrucrture devices were carried out. We successfully achieved preliminary detection and emission results with the first 2 devices and those results have been presented in international conferences such as Optical Terahertz Science and Technology in San Diego, USA, March 8 - 13, 2015
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project is progressing smoothly as we planned. The design and fabrication of first set of devices were carried out. Planned experiments were also conducted and the first results was presented in international conferences.
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| Strategy for Future Research Activity |
For the second year, I will design and fabricate new and optimized structures devices. The analysis of results we obtained in the first year shows that having devices with clear and pronounce negative dynamic conductance (NDC) is mandatory. The NDC in those structures strongly depends on the relative crystallographic orientation between the two graphene layers (GLs). In order to observe it the two layers have to be aligned so that their crystallographic axes are parallel. The misalignment angles between the two GLs crystallographic axes in our previous devices are about 30 degree and the target for the second year devices will be misalignment angles of about 1 degree.
Right after we will conducted terahertz (THz) photo-emission and detection measurements. We expect few order of magnitude improvement in the devices sensitivity and emission power. The second year experiments will be similar to those performed in the first year with the reference devices. Additional type of experiments will also be carried out in terms of THz time domain spectroscopy to measure THz gain in devices with NDC. The THz gain is associated with photon assisted resonant tunneling transitions and will confirm the possibility of realization of efficient THz photo-detectors and lasers using DGL heterostructures. Devices sensitivity, emission spectra, responsivity and noise equivalent power and frequency tunability range will be evaluated.
The theoretical analysis will be done in collaboration with Prof. Victor Ryzhii and Dr Akira Satou, visiting and assistant professors in my current team
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