S. L. Rumyantsev

Nonresonant detection of terahertz radiation in field effect transistors

We present an experimental and theoretical study of nonresonant detection of subterahertz radiation in GaAs/AlGaAs and GaN/AlGaN heterostructure field effect transistors. The experiments were performed in a wide range of temperatures (8–300 K) and for frequencies ranging from 100 to 600 GHz. The photoresponse measured as a function of the gate voltage exhibited a maximum near the threshold voltage. The results were interpreted using a theoretical model that shows that the maximum in photoresponse can be explained by the combined effect of exponential decrease of the electron density and the gate leakage current.

Plasma wave detection of terahertz radiation by silicon field effects transistors: Responsivity and noise equivalent power

Si metal oxide semiconductor field effect transistors (MOSFETs) with the gate lengths of 120–300nm have been studied as room temperature plasma wave detectors of 0.7THz electromagnetic radiation. In agreement with the plasma wave detection theory, the response was found to depend on the gate length and the gate bias. The obtained values of responsivity (⩽200V∕W) and noise equivalent power (⩾10−10W∕Hz0.5) demonstrate the potential of Si MOSFETs as sensitive detectors of terahertz radiation.

Plasma wave detection of sub-terahertz and terahertz radiation by silicon field-effect transistors

We report on experiments on photoresponse to sub-THz (120GHz) radiation of Si field-effect transistors (FETs) with nanometer and submicron gate lengths at 300K. The observed photoresponse is in agreement with predictions of the Dyakonov–Shur plasma wave detection theory. This is experimental evidence of the plasma wave detection by silicon FETs. The plasma wave parameters deduced from the experiments allow us to predict the nonresonant and resonant detection in THz range by nanometer size silicon devices—operating at room temperature.

Selective Gas Sensing with a Single Pristine Graphene Transistor

We show that vapors of different chemicals produce distinguishably different effects on the low-frequency noise spectra of graphene. It was found in a systematic study that some gases change the electrical resistance of graphene devices without changing their low-frequency noise spectra while other gases modify the noise spectra by inducing Lorentzian components with distinctive features. The characteristic frequency f(c) of the Lorentzian noise bulges in graphene devices is different for different chemicals and varies from f(c) = 10-20 Hz to f(c) = 1300-1600 Hz for tetrahydrofuran and chloroform vapors, respectively. The obtained results indicate that the low-frequency noise in combination with other sensing parameters can allow one to achieve the selective gas sensing with a single pristine graphene transistor. Our method of gas sensing with graphene does not require graphene surface functionalization or fabrication of an array of the devices with each tuned to a certain chemical.

Resonant detection of subterahertz and terahertz radiation by plasma waves in submicron field-effect transistors

We report on the experiments on resonant photoresponse of the gated two-dimensional electron gas to the terahertz radiation. The visible-light-induced, metastable increase of the carrier density in the transistor channel shifts the resonance position to the higher gate voltages, in agreement with plasma wave detection theory. In this way, an unambiguous proof of the origin of the observed resonant detection is provided. The visible light illumination also leads to an increase of the electron mobility and, as a result, to an increase of the resonant detection quality factor. Resonant detection of the harmonics of the Gunn diode-based emission system is demonstrated up to 1.2 THz.

Resonant and voltage-tunable terahertz detection in InGaAs∕InP nanometer transistors

The authors report on detection of terahertz radiation by high electron mobility nanometer InGaAs∕AlInAs transistors. The photovoltaic type of response was observed at the 1.8–3.1THz frequency range, which is far above the cutoff frequency of the transistors. The experiments were performed in the temperature range from 10to80K. The resonant response was observed and was found to be tunable by the gate voltage. The resonances were interpreted as plasma wave excitations in the gated two-dimensional electron gas. The minimum noise equivalent power was estimated, showing possible application of these transistors in sensing of terahertz radiation.

Resonant detection of subterahertz radiation by plasma waves in a submicron field-effect transistor

The resonant detection of subterahertz radiation by two-dimensional electron plasma confined in a submicron gate GaAs/AlGaAs field-effect transistor is demonstrated. The results show that the critical parameter that governs the sensitivity of the resonant detection is ωτ, where ω is the radiation frequency and τ is the momentum scattering time. By lowering the temperature and hence increasing τ and increasing the detection frequency ω, we reached ωτ∼1 and observed resonant detection of 600 GHz radiation in a 0.15 μm gate length GaAs field-effect transistor. The evolution of the observed photoresponse signal with temperature and frequency is reproduced well within the framework of a theoretical model.

Room-temperature plasma waves resonant detection of sub-terahertz radiation by nanometer field-effect transistor

We report on room-temperature, resonant detection of 0.6THz radiation by 250nm gate length GaAs∕AlGaAs heterostructure field-effect transistor. We show that the detection is strongly increased (and becomes resonant) when the drain current increases and the transistor is driven into the current saturation region. We interpret the results as due to resonant plasma wave detection that is enhanced by increasing the electron drift velocity.

Low-frequency electronic noise in the double-gate single-layer graphene transistors

We report results of experimental investigation of the low-frequency noise in the topgate graphene transistors. The back-gate graphene devices were modified via addition of the top gate separated by ~20 nm of HfO2 from the single-layer graphene channels. The measurements revealed low flicker noise levels with the normalized noise spectral density close to 1/f (f is the frequency) and Hooge parameter H  210 -3 . The analysis of noise spectral density dependence on the top and bottom gate biases helped us to elucidate the noise sources in these devices and develop a strategy for the electronic noise reduction. The obtained results are important for all proposed graphene applications in electronics and sensors.

Electrical and noise characteristics of graphene field-effect transistors: ambient effects, noise sources and physical mechanisms

Low frequency noise in virgin (not aged) graphene transistors might be relatively low (comparable to average Si MOSFETs), at least for high quality devices with the bottom gate configuration. Graphene channels are the dominant sources of noise, even though the contact resistances have an important effect on the noise magnitude due to the voltage re-distribution between the contacts and the channel. Gate voltage dependences of noise in graphene transistors reveal that the noise mechanism cannot be described by a conventional McWhorter model and might be linked to graphene mobility fluctuations. Aging in ambience causes a substantial degradation of device characteristics and increase of noise level. The temperature dependences of the current-voltage characteristics of graphene revealed a new effect of a “memory step” near the charge neutrality voltage. Further studies of low frequency noise under such conditions might help in understanding of this novel phenomenon.