In this paper, we have experimentally demonstrated the engineering of semi-metal single layer CVD Graphene’s bandgap by decorating with randomly distributed ZnO nano-seed grown by sonication of Zinc acetate dehydrate. The proximity of nanoparticles and Graphene breaks Graphene’s sublattice symmetry and opens-up a bandgap. The 2-D/G ratio of Raman spectroscopy of decorated Graphene along with a peak at 432.39 cm<sup>-1</sup> confirmed presence of ZnO on single layer Graphene. The introduced bandgap was measured from the slope of Arrhenius plot. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for digital and logic applications.
In this work, we propose a novel Graphene field effect transistor (GFET) with ohmic Source/Drain contacts having capacitive extension towards the Gate. The ohmic contacts of the proposed GFET are used for DC biasing as like as conventional GFETs whereas their extended parts which are capacitively coupled to the channel reduce access region length as well as the access resistance and provide a low impedance route for the high frequency RF signal. Reduction of access resistance along with the paralleling of ohmic contact resistance and real part of capacitive impedance result in an overall lower Source/Drain resistance which eventually increases the current gain cut-off frequency, <i>f<sub>T</sub></i>. We have studied and compared the DC and RF characteristics of the baseline conventional GFET and proposed GFET using analytical and numerical techniques.
We propose and extensively analyze a novel Graphene-FET (GFET) with two capacitively coupled field-controlling electrodes (FCE) at the ungated access regions between gate and source/drain. The FCEs are proposed to be positioned both on top and bottom of the device. The FCEs could be independently biased to modulate sheet carrier concentration and thereby the resistance in the ungated regions. The reduction of source/drain access resistance results in increased cut off frequency compared to those of conventional GFETs with the same geometry. The DC and improved RF characteristics of the proposed device have been studied using both analytical and numerical techniques and compared with the baseline designs.
We theoretically investigated and designed a tunable, compact THz source in 1-10 THz range based on a nonlinear
optical microdisk resonator. The lack of tunable THz source operating at room temperature is still one of the major
impediments for the applications of THz radiation. The proposed device on an insulated borosilicate glass substrate
consists of a nonlinear optical disk resonator on top of another disk capable of sustaining THz modes. A pair of Si
optical waveguides is coupled to the nonlinear microdisk in order to carry the two input optical waves. Another pair of Si
THz waveguides is placed beneath the input optical waveguides to couple out the generated THz radiation from the disk
to receiver antenna. Both optical and THz disks are engineered optimally with necessary effective mode indices in order
to satisfy the phase matching condition. We present the simulation results of our proposed device using a commercial
finite element simulation tool. A distinguished THz peak coincident exactly with the theoretical calculations involving
DFG is observed in frequency spectrum of electric field in the microdisk resonator. Our device has the potential to
enable tunable, compact THz emitters and on-chip integrated spectrometers.
Analytical and numerical studies of the dispersion properties of grating gated THz plasmonic structures show that
the plasmonic crystal dispersion relation can be represented in terms of effective index of the dielectric medium
around the 2DEG for the plasmons. Forbidden energy band gaps are observed at Brillion zone boundaries of the
plasmonic crystal. FDTD calculations predict the existence of the plasmonic modes with symmetrical, antisymmetrical
and asymmetrical charge distributions. Breaking the translational symmetry of the crystal lattice by
changing the electron concentration of the two dimensional electron gas (2DEG) under a single gate line in every 9th gate induces a cavity state. The induced cavity state supports a weekly-coupled cavity mode.
We designed and theoretically investigated nonlinear optical micro-ring resonators for tunable terahertz (THz) emission
in 1-10 THz range by using difference frequency generation (DFG) phenomenon with large second order optical
nonlinearity (χ(<sup>2</sup>)). Our design consists of a nonlinear ring resonator and another ring underneath capable of sustaining high-Q resonant modes for infrared pump beams and the generated THz radiation, respectively. The nonlinear ring
resonator generates THz through DFG by mixing the input waves carried by a pair of waveguides. The proposed device
can be a viable platform for tunable, compact THz emitters and on-chip integrated spectrometers.
We report on sub-wavelength THz plasmonic split ring resonators on 2 dimensional electron gas (2DEG) at AlGaN/GaN
hetero-interface and on oxide coated high mobility graphene. The investigated in this study guide THz electric field into
deep sub-wavelength scale by plasmonic excitations. Propagation of a broadband pulse of EM waves was simulated by
using a commercial FDTD simulation tool. The results show that split ring resonator structures can be used to guide THz
into deep sub-wavelength down λ/200 and achieve relatively higher quality factors than grating gate devices by
plasmonic confinement which can be used for THz detection, filtering and possibly for THz on-chip-spectrometer.
Moreover, ring resonator modes supported by system can be tuned with an applied voltage to gratings.
We report on sub-wavelength THz plasmonic lenses based on 2 dimensional electron gas (2DEG) at AlGaN/GaN
interface and also on few-layer graphene sheets. Circular gratings investigated in this study concentrate THz electric
field into deep sub-wavelength scale by plasmonic excitations polarization independently. Propagation of a broadband
pulse of EM waves in 0.5-10 THz was simulated by using a commercial FDTD simulation tool. The results show that
concentric plasmonic grating structures can be used to concentrate THz into deep sub-wavelength down to λ/350 spot
size and achieve very large field enhancements by plasmonic confinement which can be used for THz detection and
possibly for sub-wavelength imaging. Electric field intensity under the central point can be orders of magnitude higher
than the outer grating area. Moreover, plasmonic lens modes supported by system can be tuned with an applied voltage