Terahertz lasers based on optically pumped multiple graphene structures with slot-line and dielectric waveguides

Bukvic

J. Phys. D: Appl. Phys.

et al. 2016

Abstract. Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying electrical length of a resonator. Presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. Frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene-metal combined waveguide resonators are proposed in order to preserve excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices.

Section: Full-wave Electromagnetic Analysissupporting

confidence: 81%

Graphene-based waveguide resonators for submillimeter-wave applications

Bukvic

J. Phys. D: Appl. Phys.

et al. 2016

Applied Physics Letters

“…The THz gain of the TM mode in the laser under consideration is at least comparable the maximum THz gain (without the Drude losses) in the injection lasers utilizing the TE mode and the intra-GL radiative transitions (see, for instance, Ref. [6]). Hence the former device can exhibit advantages due to the effective suppression of the Drude absorption.…”

mentioning

confidence: 94%

“…[19,20]). This can provide the superiority of the double-GL lasers under consideration over the GL-based lasers using the intra-GL transitions discussed previously [4][5][6] and QCL lasers [12,31] at elevated temperatures in the low end of the THz range as well as in the range where the operation of QCLs is hampered by the optical phonon absorption.…”

mentioning

confidence: 99%

“…In particular, the interband population inversion and the pertinent negativity of the dynamic conductivity in GLs [2,3] due to the optical or injection pumping can be used in GL-based THz lasers [4][5][6][7][8][9]. First experimental results on the THz emission from optically excited GLs [10] (see also review paper [11] and references therein) instill confidence in the realization of such lasers.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Injection terahertz laser using the resonant inter-layer radiative transitions in double-graphene-layer structure

Ryzhii

Dubinov

Aleshkin

et al. 2013

Self Cite

We propose and substantiate the concept of terahertz (THz) laser enabled by the resonant electron radiative transitions between graphene layers (GLs) in double-GL structures. We estimate the THz gain for TM-mode exhibiting very low Drude absorption in GLs and show that the gain can exceed the losses in metal-metal waveguides at the low end of the THz range. The spectrum of the emitted photons can be tuned by the applied voltage. A weak temperature dependence of the THz gain promotes an effective operation at room temperature.The gapless energy spectrum of graphene layers (GLs) [1] enables the creation of different terahertz (THz) devices utilizing the interband transition. In particular, the interband population inversion and the pertinent negativity of the dynamic conductivity in GLs [2,3] due to the optical or injection pumping can be used in GL-based THz lasers [4][5][6][7][8][9]. First experimental results on the THz emission from optically excited GLs [10] (see also review paper [11] and references therein) instill confidence in the realization of such lasers. One of the obstacles, limiting the achievement of the negative dynamic conductivity in the range of a few THz, is the reabsorption of the photons with the in-plane polarization emitted at the interband transitions due to the intraband transitions (the Drude absorption). Similar situation takes place in the quantum cascade lasers (QCLs) based on multiple quantum well (MQW) structures [12]. However, in the case of the photon polarization perpendicular to the QW plane the intraband (intrasubband) absorption can be much weaker than that following from the semi-classical Drude formula [13].In this paper, we propose a device structure based on a double-GL structure shown in Fig. 1 (upper panel) with the injection of electrons to one n-doped GL and to another p-doped GL, which can be used for lasing of THz photons with the electric field perpendicular to the GL plane due to the tunneling inter-GL radiative processes. The structure band diagram under the applied bias voltage and tunneling transitions assisted with the emission of photons with the energy ω ∼ ∆, where ∆ is the energy distance (gap) between the Dirac points in GLs, are demonstrated in Fig. 1 (lower panel). These transitions take place from the conduction band of the GL with 2DEG to the empty conduction band of GL with 2DHG. The transition from the filled valence band the former GL to the empty portion of the valence band of the latter GL also contribute to the emission of photons with ω ∼ ∆. The structure comprises two GLs with the side contact at one of the GL edges. This double-GL structure plays the role of the laser active region. The opposite edge of GL is isolated from another contact. A narrow tunneling-transparent barrier separates GLs (its thickness d is about few nanometers). The applied bias voltage V provides the formation of the two-dimensional electron and hole gases (2DEG and 2DHG) in the upper and lower GLs, respectively owing to the injection from the side contacts, so that the ...

Journal of Applied Physics

“…The gapless energy spectrum of graphene layers allows to use them in terahertz and midinfrared detectors and lasers [5][6][7][8][9]. However, the gapless energy spectrum of GLs is an obstacle for creating transistor digital circuits based on graphene field-effect transistors (G-FETs) due to relatively strong interband tunneling in the FET offstate [10,11].…”

Section: Introductionmentioning

confidence: 99%

Analytical device model for graphene bilayer field-effect transistors using weak nonlocality approximation

Ryzhii

Satou

et al. 2011

Self Cite

We develop an analytical device model for graphene bilayer field-effect transistors (GBL-FETs) with the back and top gates. The model is based on the Boltzmann equation for the electron transport and the Poisson equation in the weak nonlocality approximation for the potential in the GBL-FET channel. The potential distributions in the GBL-FET channel are found analytically. The source-drain current in GBL-FETs and their transconductance are expressed in terms of the geometrical parameters and applied voltages by analytical formulas in the most important limiting cases. These formulas explicitly account for the short-gate effect and the effect of drain-induced barrier lowering. The parameters characterizing the strength of these effects are derived. It is shown that the GBL-FET transconductance exhibits a pronounced maximum as a function of the top-gate voltage swing. The interplay of the short-gate effect and the electron collisions results in a nonmonotonic dependence of the transconductance on the top-gate length.