H. Marinchio

Terahertz spectroscopy of plasma waves in high electron mobility transistors

We report on systematic measurements of resonant plasma waves oscillations in several gate-length InGaAs high electron mobility transistors (HEMTs) and compare them with numerical results from a specially developed model. A great concern of experiments has been to ensure that HEMTs were not subject to any spurious electronic oscillation that may interfere with the desired plasma-wave spectroscopy excited via a terahertz optical beating. The influence of geometrical HEMTs parameters as well as biasing conditions is then explored extensively owing to many different devices. Plasma resonances up to the terahertz are observed. A numerical approach, based on hydrodynamic equations coupled to a pseudo-two-dimensional Poisson solver, has been developed and is shown to render accurately from experiments. Using a combination of experimental results and numerical simulations all at once, a comprehensive spectroscopy of plasma waves in HEMTs is provided with a deep insight into the physical processes that are involved.

Hydrodynamic modeling of optically excited terahertz plasma oscillations in nanometric field effect transistors

We present a hydrodynamic model to simulate the excitation by optical beating of plasma waves in nanometric field effect transistors. The biasing conditions are whatever possible from Ohmic to saturation conditions. The model provides a direct calculation of the time-dependent voltage response of the transistors, which can be separated into an average and a harmonic component. These quantities are interpreted by generalizing the concepts of plasma transit time and wave increment to the case of nonuniform channels. The possibilities to tune and to optimize the plasma resonance at room temperature by varying the drain voltage are demonstrated.

Problems of noise modeling in the presence of total current branching in high electron mobility transistor and field-effect transistor channels

In the framework of analytical and hydrodynamic models for the description of carrier transport and noise in high electron mobility transistor/field-effect transistor channels the main features of the intrinsic noise of transistors are investigated under continuous branching of the current between channel and gate. It is shown that the current-noise and voltage-noise spectra at the transistor terminals contain an excess noise related to thermal excitation of plasma wave modes in the dielectric layer between the channel and gate. It is found that the set of modes of excited plasma waves can be governed by the external embedding circuits, thus violating a universal description of noise in terms of Norton and Thevenin noise generators.

Room temperature coherent and voltage tunable terahertz emission from nanometer-sized field effect transistors

We report on reflective electro-optic sampling measurements of terahertz emission from nanometer-gate-length InGaAs-based high electron mobility transistors. The room temperature coherent gate-voltage tunable emission is demonstrated. We establish that the physical mechanism of the coherent terahertz emission is related to the plasma waves driven by simultaneous current and optical excitation. A significant shift of the plasma frequency and the narrowing of the emission with increasing channel’s current are observed and explained as due to the increase in the carriers’ density and drift velocity.

Room-temperature terahertz mixer based on the simultaneous electronic and optical excitations of plasma waves in a field effect transistor

A method for the heterodyne detection of terahertz (THz) signals is proposed. A high electron mobility transistor is used as a nonlinear element, while the optical beating of two laser beams exciting plasma waves in the transistor channel plays the role of the THz local oscillator. High efficiency and room-temperature operation of such a mixer are demonstrated by numerical simulations.

Plasma waves subterahertz optical beating detection and enhancement in long-channel high-electron-mobility transistors: experiments and modeling

A photomixed laser beam of two 1.55 mum continuous-wave lasers is used for interband photoexcitation in submicron gate length InAlAs/InGaAs transistors. Results show the clear excitation of plasma oscillation modes in the transistor channel. A strong amplification of the optical beating detection in the 0-600 GHz range is observed as a function of drain-source voltage. Numerical results, using hydrodynamic model coupled to a pseudo-2D Poisson equation, are in good agreement with experiments concerning the plasma frequency dependence with gate voltage. Moreover, this model confirms both optical beating detection at subterahertz frequencies and the enhancement observed when drain-source voltage increases.

Enhanced THz Detection Through Phase-Controlled Current Response in Field-Effect Transistors

A field effect transistor can be used as a nonlinear element for the resonant detection of incident terahertz (THz) radiation at room temperature. The excitation of the plasma modes in the channel significantly increases the detection efficiency in the THz range. By means of a numerical hydrodynamic model, we study the drain-current response of a high electron mobility transistor to a THz signal applied on its gate and/or on its drain contacts to obtain the optimal configuration in terms of detection. We demonstrate that the amplitudes of the harmonic and average drain-current responses associated with the presence of plasma modes in the channel strongly depend on which transistor terminal collects the incident THz radiation and that a maximum dcresponse can be obtained by appropriately dephasing the two electrode signals.

Terahertz emission induced by optical beating in nanometer-length field-effect transistors

We report on photo-induced terahertz radiation with a high spectral purity generated by a submicron sized InGaAs-based high-electron-mobility transistor. The emission peak is due to the electron-hole pairs photocreated in the transistor channel at the frequency of the beating of two cw-laser sources. The radiation frequency corresponds to the lowest fundamental plasma mode in the gated region of the transistor channel. The observed high emission quality factor at 200 K is interpreted as a result of stream-plasma instability in the two-dimensional electron gas whose appearance is emphasized by the reduction of the velocity relaxation rate with the temperature.

Plasma resonances in a gated semiconductor slab of arbitrary thickness

We present an analytical model suitable for the study of the plasma modes in gated semiconductor slabs of arbitrary thickness. A pseudo-two-dimensional Poisson equation allows us to consider both transverse and longitudinal electric field variations. We calculate the dispersion relation demonstrating the dispersive nature of the slab. We express the frequencies of the plasma modes appearing in a cavity. A transition from a two-dimensional to a three-dimensional behavior is revealed when the transverse dimension of the device or the order of modes grow. These analytical results show a good agreement with Monte Carlo calculations of the voltage noise spectrum.

Monte Carlo investigation of terahertz plasma oscillations in gated ultrathin channel of n-InGaAs

By numerical simulations we investigate the dispersion of the plasma frequency in a gated channel of n-type InGaAs layer of thickness W and submicron length L at T=300 K. In the presence of a source-drain voltage and for a carrier concentrations of 1018 cm−3 the spectra evidences a peaked shape with two main bumps, the former at high frequency corresponding to the three-dimensional plasma frequency and the latter at a low frequency. The frequency value of the latter peak exhibits a dispersion as the inverse of the channel length in agreement with the predictions of gradual channel approximation. At increasing drain voltages the instabilities associated with the presence of Gunn domains are responsible for a suppression of the plasma peak in favor of the onset of a peak in the subterahertz domain associated with transit time effects.