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Engineer, physicist and entrepreuneredit
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We propose and analyze an electro-optical modulator based on a gated graphene structure and utilizing the electrically-controlled Pauli blocking. It is demonstrated that the resonant excitation of plasma oscillations can lead to a... more
We propose and analyze an electro-optical modulator based on a gated graphene structure and utilizing the electrically-controlled Pauli blocking. It is demonstrated that the resonant excitation of plasma oscillations can lead to a substantial enhancement of the modulation efficiency in the terahertz range of modulation frequencies.
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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... more
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 to surpass 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 with previously proposed GBL-based THz lasers.
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Scanning near-field photoluminescence (PL) spectroscopy was applied to study spatial variations of emission spectra of AlxGa1−xN epilayers with 0.6≤x≤0.7. PL spectra were found to be spatially uniform with peak wavelength standard... more
Scanning near-field photoluminescence (PL) spectroscopy was applied to study spatial variations of emission spectra of AlxGa1−xN epilayers with 0.6≤x≤0.7. PL spectra were found to be spatially uniform with peak wavelength standard deviations of only ∼2 meV and ratios between peak intensity standard deviations and average peak intensity values of 0.06. The observed absence of correlation between the PL peak wavelength and intensity shows that spatial distribution of nonradiative recombination centers is not related to band potential fluctuations. Our results demonstrate that the homogeneous broadening and the random cation distribution primarily determine PL linewidths for layers grown under optimized conditions.
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We experimentally and numerically analyze the charge transfer THz plasmons using an asymmetric plasmonic assembly of metallic V-shaped blocks. The asymmetric design of the blocks allows for the excitation of classical dipolar and... more
We experimentally and numerically analyze the charge transfer THz plasmons using an asymmetric plasmonic assembly of metallic V-shaped blocks. The asymmetric design of the blocks allows for the excitation of classical dipolar and multipolar modes due to the capacitive coupling. Introducing a conductive microdisk between the blocks, we facilitated the excitation of the charge transfer plasmons and studied their characteristics along with the capacitive coupling by varying the size of the disk.
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We report on fabrication of MoS2 thin-film transistors (TFTs) and experimental investigations of their high-temperature current-voltage characteristics. The measurements show that MoS2 devices remain functional to temperatures of at least... more
We report on fabrication of MoS2 thin-film transistors (TFTs) and experimental investigations of their high-temperature current-voltage characteristics. The measurements show that MoS2 devices remain functional to temperatures of at least as high as 500 K. The temperature increase results in decreased threshold voltage and mobility. The comparison of the direct current (DC) and pulse measurements shows that the direct current sub-linear and super-linear output characteristics of MoS2 thin-films devices result from the Joule heating and the interplay of the threshold voltage and mobility temperature dependences. At temperatures above 450 K, a kink in the drain current occurs at zero gate voltage irrespective of the threshold voltage value. This intriguing phenomenon, referred to as a “memory step,” was attributed to the slow relaxation processes in thin films similar to those in graphene and electron glasses. The fabricated MoS2 thin-film transistors demonstrated stable operation aft...
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Engineering, Physics, Low Frequency, Optoelectronics, Quantum Efficiency, and 12 moreQuantum Wells, Spontaneous Emission, Light Intensity, Quantum Well, Low Frequency Noise, Superposition, 1/f Noise, Noise Measurement, Spectral Density, Quantum Yield, Light Emitting Diode, and External Quantum Efficiency
Page 1. Low Frequency Noise in 4H-SiC MOSFETs Sergey L. Rumyantsev 1,a , Michael S. Shur 1,b , Michael E. Levinshtein 2,c , Pavel A. Ivanov 2,d , John W. Palmour 3,e , Mrinal K. Das 3,f and Brett A. Hull 3,g 1Rensselaer Polytechnic... more
Page 1. Low Frequency Noise in 4H-SiC MOSFETs Sergey L. Rumyantsev 1,a , Michael S. Shur 1,b , Michael E. Levinshtein 2,c , Pavel A. Ivanov 2,d , John W. Palmour 3,e , Mrinal K. Das 3,f and Brett A. Hull 3,g 1Rensselaer Polytechnic Institute, Troy NY 12180-3590, USA ...
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This paper reviews recent advances toward new types of terahertz (THz) lasers using active plasmonics in graphene. Optical gain originated from graphene ultrafast nonequilibrium carrier dynamics and phonon properties in the broadband THz... more
This paper reviews recent advances toward new types of terahertz (THz) lasers using active plasmonics in graphene. Optical gain originated from graphene ultrafast nonequilibrium carrier dynamics and phonon properties in the broadband THz frequency range might pave the way for the THz lasers but the challenge is to overcome the strong losses in the THz range. Graphene plasmons, quanta of the collective charge density waves excited by the two-dimensional carriers in graphene, can substantially enhance the light-matter (THz photons-graphene) interaction, leading to a “giant THz gain”. One possible implementation relies on superradiant plasmonic THz lasing in graphene-metal micro-ribbon array structures.
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The influence of strong magnetic field on the 1/f noise in AlGaN/GaN metal-oxide-Semiconductor heterostructure field effect transistors (MOSHFETs) has been studied. The independence of 1/f noise on the magnetic fields up to 10 T where the... more
The influence of strong magnetic field on the 1/f noise in AlGaN/GaN metal-oxide-Semiconductor heterostructure field effect transistors (MOSHFETs) has been studied. The independence of 1/f noise on the magnetic fields up to 10 T where the strong geometric magneto-resistance has been observed, shows that the carrier number fluctuations is the dominant mechanism of the noise in these devices.
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Optical gain in GaN epilayers was investigated by using the variable stripe length (VSL) technique. The light amplification was studied for the propagation directions along and perpendicular to the layer surface. Experimental stripe... more
Optical gain in GaN epilayers was investigated by using the variable stripe length (VSL) technique. The light amplification was studied for the propagation directions along and perpendicular to the layer surface. Experimental stripe length and excitation intensity dependencies were measured and saturation of gain modes and appearance of new modes was observed. The limitations of the VSL technique due to gain saturation and one-dimensional light propagation model are discussed. Gain peak values up to ∼7500cm−1 (which is the limit of applicability of the VSL technique) have been demonstrated in GaN epilayers grown on AlN buffer layers deposited on sapphire by migration enhanced metal-organic chemical vapor deposition.
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Low-frequency noise in Al 0.4 Ga 0.6 N thin films (50 nm) was measured at room and elevated temperatures as function of gate and drain voltages. Both 1/f noise and generation-recombination noise were observed. Hooge parameter, α, was... more
Low-frequency noise in Al 0.4 Ga 0.6 N thin films (50 nm) was measured at room and elevated temperatures as function of gate and drain voltages. Both 1/f noise and generation-recombination noise were observed. Hooge parameter, α, was estimated to be about 7. The activation energy for observed generation-recombination noise was found to be Ea ~ 1.0 eV . This activation energy is consistent with the activation energy observed for g-r noise in AlGaN/GaN HFETs.
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Low frequency fluctuations in light intensity of 340 nm and 280 nm GaN -based light emitting diodes (LEDs) are compared with noise properties of other commercially available UV and visible wavelength LEDs and halogen lamps. At low... more
Low frequency fluctuations in light intensity of 340 nm and 280 nm GaN -based light emitting diodes (LEDs) are compared with noise properties of other commercially available UV and visible wavelength LEDs and halogen lamps. At low frequencies, LEDs can exhibit lower levels of noise than halogen lamps. An LED noise quality factor β is estimated for the UV LEDs.
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Strain and polarization control achieved via strain energy band engineering is the key for achieving stable and reliable operation of wide bad gap devices. In this paper, we consider the application of this approach to novel... more
Strain and polarization control achieved via strain energy band engineering is the key for achieving stable and reliable operation of wide bad gap devices. In this paper, we consider the application of this approach to novel AlN/GaN/InN-based field effect transistors and ultraviolet light emitting diodes.
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III-Nitride Metal-Oxide-Semiconductor Heterojunction (MOSH) structure consists of a thin dielectric layer deposited on top of a semiconductor heterostructure with a 2D electron gas at the heterojunction interface. MOSH structures are the... more
III-Nitride Metal-Oxide-Semiconductor Heterojunction (MOSH) structure consists of a thin dielectric layer deposited on top of a semiconductor heterostructure with a 2D electron gas at the heterojunction interface. MOSH structures are the key components for high-power low-loss, fast RF switches. The paper discusses two types of high-power switches using III-Nitride MOSH structures. The first type uses the MOSH structure as the gate region of an AlGaN/GaN HFET. The second type uses MOSH structure as a switching capacitor. In the 2GHz - 10 GHz frequency range, switching powers from 20 to 60 W/mm have been achieved with the insertion loss below 1 dB.
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Materials Science, Optoelectronics, Semiconductor, RF, Capacitor, and 5 moreOxide, Nitride, Switch, HEMT, and Heterojunction
We demonstrate a novel highly sensitive UV sensor based on RF LC oscillator with an optical frequency modulation due to the photocapacitive effect in an interdigitated aluminum-on-GaN/sapphire structure. In the range from 280 nm to 325... more
We demonstrate a novel highly sensitive UV sensor based on RF LC oscillator with an optical frequency modulation due to the photocapacitive effect in an interdigitated aluminum-on-GaN/sapphire structure. In the range from 280 nm to 325 nm, the sensor exhibits extremely high sensitivity of 60 KHz/¿W/cm2 at low UV powers (¿30 ¿W). The maximum oscillator frequency shift of 4 MHz
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ABSTRACT 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... more
ABSTRACT 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.
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ABSTRACT
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We propose a model of the 1∕f noise in GaN∕AlGaN heterojunction field-effect transistors that links the 1∕f noise to the tunneling from the two-dimensional electron gas in the device channel into the tail states near the conduction band... more
We propose a model of the 1∕f noise in GaN∕AlGaN heterojunction field-effect transistors that links the 1∕f noise to the tunneling from the two-dimensional electron gas in the device channel into the tail states near the conduction band of the GaN layer. The model predicts a fairly weak temperature dependence of the 1∕f noise in the temperature interval from 50 to 600 K with the value of the Hooge parameter α within the range of 10−3–10−5. Both these predictions are in agreement with experimental data.
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... 17, pp. 36173619, Oct. 2003. [5] P. Sharma, S. Kumar, and K. Sreenivas, Interaction of surface acoustic waves and ultraviolet light in ZnO films, J. Mater. Res., vol. 18, no. 3, pp. ... Phys. Lett., vol. 84, no. 16, pp. 31663168,... more
... 17, pp. 36173619, Oct. 2003. [5] P. Sharma, S. Kumar, and K. Sreenivas, Interaction of surface acoustic waves and ultraviolet light in ZnO films, J. Mater. Res., vol. 18, no. 3, pp. ... Phys. Lett., vol. 84, no. 16, pp. 31663168, Apr. 2004. [7] D. Ciplys, MS Shur, N. Pala, A. Sereika, R ...
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Abstract We report on a 0.15-μm gate length AlGaN/GaN doped channel heterostructure field effect transistor (DC-HFET) with maximum frequency of oscillation in excess of 97 GHz. HFETs based on our doped channel design exhibited CW... more
Abstract We report on a 0.15-μm gate length AlGaN/GaN doped channel heterostructure field effect transistor (DC-HFET) with maximum frequency of oscillation in excess of 97 GHz. HFETs based on our doped channel design exhibited CW microwave operation up to 15 ...
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Abstract—We report on the first metal–oxide–semiconductor AlGaN/GaN radio-frequency (RF) switch with capacitively cou-pled contacts using a HfO2 layer as the gate dielectric and sur-face passivation layer. The new insulating-gate RF... more
Abstract—We report on the first metal–oxide–semiconductor AlGaN/GaN radio-frequency (RF) switch with capacitively cou-pled contacts using a HfO2 layer as the gate dielectric and sur-face passivation layer. The new insulating-gate RF switch has a lower leakage current and can handle higher RF powers than AlGaN/GaN HFET switches. Index Terms—AlGaN/GaN, capacitive coupling, high-k dielec-tric, HfO2, radio-frequency (RF) switch. I.