Graphene Tunneling Transit-Time Terahertz Oscillator Based on Electrically Induced p–i–n Junction (original) (raw)
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Negative terahertz dynamic conductivity in electrically induced lateral p–i–n junction in graphene
Physica E: Low-dimensional Systems and Nanostructures, 2010
We analyze a graphene tunneling transit-time device based on a heterostructure with a lateral p-i-n junction electrically induced in the graphene layer and calculate its ac characteristics. Using the developed device model, it is shown that the ballistic transit of electrons and holes generated due to interband tunneling in the i-section results in the negative ac conductance in the terahertz frequency range. The device can serve as an active element of terahertz oscillators
Journal of Applied Physics, 2013
We develop a device model for p-i-n tunneling transit-time diodes based on single-and multiple graphene layer structures operating at the reverse bias voltages. The model of the graphene tunneling transit-time diode (GTUNNETT) accounts for the features of the interband tunneling generation of electrons and holes and their ballistic transport in the device i-section, as well as the effect of the self-consistent electric field associated with the charges of propagating electrons and holes. Using the developed model, we calculate the dc current-voltage characteristics and the small-signal ac frequency-dependent admittance as functions of the GTUNNETT structural parameters, in particular, the number of graphene layers and the dielectric constant of the surrounding media. It is shown that the admittance real part can be negative in a certain frequency range. As revealed, if the i-section somewhat shorter than one micrometer, this range corresponds to the terahertz frequencies. Due to the effect of the self-consistent electric field, the behavior of the GTUNNETT admittance in the range of its negativity of its real part is rather sensitive to the relation between the number of graphene layers and dielectric constant. The obtained results demonstrate that GTUNNETTs with optimized structure can be used in efficient terahertz oscillators. V C 2013 American Institute of Physics. [http://dx.
Graphene-Based Periodic Gate Field Effect Transistor Structures for Terahertz Applications
We report on theoretical investigation of graphene based Field Effect Transistor (FET) structures for resonant absorption of terahertz (THz) radiation by the plasmons excited in the high sheet concentration and high carrier mobility active layers. Metallic grating gates with varying periods were used to couple the THz radiation into the plasmons in the active region of the devices. Such grating gates not only improve the coupling by providing momentum match between the incident radiation and the plasmons but also allows the control of carrier concentration in the channel by external bias. Our studies demonstrate that the proposed periodic gate FET structures of Graphene can resonantly absorb THz radiation up to 6th harmonic at room temperature. Moreover, these structures have the advantage of tunability since the resonant absorption modes strongly depend on the sheet carrier concentration in the channel which could be controlled by gate bias.
Graphene-based devices in terahertz science and technology
Journal of Physics D: Applied Physics, 2012
Graphene is a one-atom-thick planar sheet of a honeycomb carbon crystal. Its gapless and linear energy spectra of electrons and holes lead to nontrivial features such as giant carrier mobility as well as broadband flat optical response. In this paper recent advances in graphene-based devices in terahertz science and technology are reviewed. First, fundamental basis of the optoelectronic properties of graphene is introduced. Second, synthesis and crystallographic characterization of graphene material are described, particularly focused on the authors' original heteroepitaxial graphene-on-silicon technology. Third, nonequilibrium carrier relaxation and recombination dynamics in optically or electrically pumped graphene is described to introduce a possibility of negative dynamic conductivity in a wide terahertz range. Fourth, recent theoretical advances toward the creation of current-injection graphene terahertz lasers are described. Fifth, unique terahertz dynamics of the two-dimensional plasmons in graphene are described. Finally, the advantages of graphene devices for terahertz applications are summarized.
Broadband graphene terahertz modulators enabled by intraband transitions
2012
Terahertz technology promises myriad applications including imaging, spectroscopy and communications. However, one major bottleneck at present for advancing this field is the lack of efficient devices to manipulate the terahertz electromagnetic waves. Here we demonstrate that exceptionally efficient broadband modulation of terahertz waves at room temperature can be realized using graphene with extremely low intrinsic signal attenuation. We experimentally achieved more than 2.5 times superior modulation than prior broadband intensity modulators, which is also the first demonstrated graphene-based device enabled solely by intraband transitions. The unique advantages of graphene in comparison to conventional semiconductors are the ease of integration and the extraordinary transport properties of holes, which are as good as those of electrons owing to the symmetric conical band structure of graphene. Given recent progress in graphene-based terahertz emitters and detectors, graphene may offer some interesting solutions for terahertz technologies.
Journal of Applied Physics, 2003
We have considered interactions between ballistic ͑or quasiballistic͒ electrons accelerated by a dc electric field in an undoped transit space ͑T space͒ and a small ultrahigh frequency ac electric field and have calculated the linear admittance of the T space. Electrons in the T space have a conventional, nonparabolic dispersion relation. After consideration of the simplest specific case when the current is limited by the space charge of the emitted electrons, we turned to an actual case when the current is limited by a heterostructural tunnel barrier ͑B barrier͒ separating the heavily doped cathode contact and the T space. We assumed that the B barrier is much thinner than the T space and both dc and ac voltages drop mainly across the T space. The emission tunnel current through the B barrier is determined by the electric field E(0) in the T space at the boundary B barrier/T space. The more substantial is, the tunnel current limitation the higher the electric field E(0) becomes. We have shown that for a space-charge limited current the change from parabolic dispersion to the nonparabolic branch induces narrowing and closing of the frequency windows of transit-time negative conductance starting with the lowest-frequency windows. These narrowing and closing frequency windows become effective only for very high voltages U across the T space: UӷmV S 2 /2e, where m is the effective mass for the parabolic branch and V S is the saturated velocity for the nonparabolic branch. For moderate voltages U, the effects of nonparabolicity are not very substantial. The tunnel current limitation decreases the space-charge effects in the T space and diminishes the role of the detailed electron dispersion relation. As a result, restoration of the frequency windows of transit-time negative conductance and an increase in the value of this negative conductance occur. The implementation of the considered tunnel injection transit time oscillator diode promises to lead to efficient and powerful sources of terahertz range radiation.
Terahertz-wave generation using graphene
MRS Proceedings, 2012
ABSTRACTIn this paper recent advances in terahertz-wave generation in graphene are reviewed. First, fundamental basis of the optoelectronic properties of graphene is introduced. Second, nonequilibrium carrier relaxation and recombination dynamics in optically or electrically pumped graphene is described to introduce a possibility of negative dynamic conductivity in a wide terahertz range. Third, recent theoretical advances toward the creation of current-injection graphene terahertz lasers are described. Fourth, unique terahertz dynamics of the two-dimensional plasmons in graphene are described. Finally, the advantages of graphene materials and devices for terahertz-wave generation are summarized.
Negative terahertz conductivity in remotely doped graphene bilayer heterostructures
Injection or optical generation of electrons and holes in graphene bilayers (GBLs) can result in the interband population inversion enabling the terahertz (THz) radiation lasing. The intraband radiative processes compete with the interband transitions. We demonstrate that remote doping enhances the indirect interband generation of photons in the proposed GBL heterostructures. Therefore such remote doping helps surpassing the intraband (Drude) absorption and results in large absolute values of the negative dynamic THz conductivity in a wide range of frequencies at elevated (including room) temperatures. The remotely doped GBL heterostructure THz lasers are expected to achieve higher THz gain compared to previously proposed GBL-based THz lasers.
Graphene-based field-effect transistor structures for terahertz applications
SPIE Proceedings, 2012
We propose Terahertz (THz) plasmonic devices based on linearly integrated FETs (LFETs) on Graphene. LFET structures are advantageous for (THz) detection since the coupling between the THz radiation and the plasma wave is strongly enhanced over the single gate devices and accordingly higher-order plasma resonances become possible. AlGaN/GaN heterostructure LFETs with their high sheet carrier concentration and high electron mobility are promising for plasmonic THz detection. Nevertheless, our numerical studies show that room temperature resonant absorption of THz radiation by the plasmons in AlGaN/GaN LFETs is very weak even if the integration density is sufficiently large. Our simulations also demonstrate that similar LFETs on Graphene, which has very large electron mobility, can resonantly absorb THz radiation up to 5th harmonic at room temperature. Additionally, we investigated LFETs with integrated cavities on Graphene. Such Periodic Cavity LFETs substantially enhance the quality factor of the resonant modes.