Yanqing Deng

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.

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 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.

Spectroscopic characterization of explosives in the far-infrared region

Far infrared spectra of 14 commonly used explosive samples have been measured by using Fourier Transform Infrared Spectroscopy (FTIR) and THz Time-Domain Spectroscopy (THz TDS). New absorption resonances between 20 cm-1 and 650 cm-1 are reported. Below 20 cm-1, no clear absorption resonances are observed in all the explosives. There is a good consistency of far-IR spectrum measured by Far-FTIR and by THz TDS in explosives 3,5-DNA and 2,4-DNT. Observed far-IR spectrum of TNT is compared with a previously reported theoretical calculation.

Millimeter wave emission from GaN high electron mobility transistor

We report on millimeter wave electromagnetic radiation from a GaN high electron mobility transistor with the gate length of 1.5 μm at 8 K. The emission takes place at gate and drain voltages in the linear regime of operation but close to the saturation voltage with the principal emission peak at approximately 75 GHz, which is much higher than the device cut-off frequency. An explanation of this effect involves the “shallow water” plasma wave instability, with the frequency of the plasma waves decreased by the ungated regions of the device.

Low-frequency noise in GaN'AlGaN heterostructure field-effect transistors at cryogenic temperatures

The low-frequency noise in GaN/AlGaN heterostructure field-effect transistors (HFETs) was studied in the temperature range from 8 to 300 K. A contribution of generation-recombination noise with extremely small activation energy Ea=(1−3) meV was observed at T<50 K. At 70⩽T⩽150 K, the temperature dependence of noise in HFETs with a doped channel exhibited a broad maximum. The position of the maximum was practically independent of the frequency of analysis. The model linking this maximum to the electron tunneling from the channel to the silicon donor level in GaN is discussed.

On the low frequency noise mechanisms in GaN/AlGaN HFETs

The low frequency noise in GaN/AlGaN heterostructure field effect transistors (HFETs) was studied in the temperature range from 8 to 300 K. At gate biases close to the threshold, the noise came from the device region under the gate, and the Hooge parameter αch was inversely proportional to ns (α ~ 1/ns) in the entire temperature range. This dependence might be explained by electron tunnelling from the 2D gas into the traps in the adjoining GaN or AlGaN layers. At voltages close to zero, the ungated source-gate and gate-drain regions were responsible for the noise, and the Hooge constant was two orders of magnitude larger. This result is consistent with recent studies of the mechanism of the current collapse in GaN-based FETs. A notable contribution from the generation-recombination noise with activation energy 0.24 eV was observed in the temperature interval from 50 K to 150 K.

Modeling of high-dose-rate transient ionizing radiation effects in bipolar devices

We have developed a dynamic model for photoelectric effect in bipolar devices exposed to a wide range of ionizing radiation intensities. We represent the stationary and dynamic photocurrents by current sources in parallel with each p-n junction. These sources include the prompt photocurrent of the depletion regions and the delayed response associated with the buildup and discharge of excess charge carriers in the quasi-neutral (q-n) regions adjacent to the junctions. The latter are described in terms of dynamic delay times for each q-n region, which can be represented by RC equivalent delay circuits. The model has been implemented in the circuit simulator AIM-Spice and has been verified by numerical simulations.

Electron mobility and terahertz detection using silicon MOSFETs

Abstract Based on the mobility calculations, we investigate the possibility of using deep submicron silicon MOSFETs for the detection and emission of terahertz radiation via the excitation of the surface plasma waves in the device channels. This analysis shows the possibility of using the MOSFET-based terahertz detector and emitter pairs for the wireless interconnects for the future VLSI chips.

SPICE modeling of neutron displacement damage and annealing effects in bipolar junction transistors

For the purpose of simulating the effects of neutron radiation damage on bipolar circuit performance, we have developed a bipolar junction transistor SPICE model that incorporates displacement damage effects. A physics-based formalism is used for describing the radiation effects within the framework of the Gummel-Poon model. A model structure that includes the dependence of neutron fluence on the relevant SPICE parameters is outlined, from which a simplified radiation model is established. The latter is presented and implemented in AIM-Spice, and it is shown to agree quite well with experiments. Dynamic effects including annealing are also discussed.