J. Lusakowski

Non Resonant Response to Terahertz Radiation by Submicron CMOS Transistors

Experimental investigations on detection of terahertz radiation are presented. We used plasma wave instability phenomenon in nanometer Silicon field effect transistor. A 30 nm gate length transistor was illuminated by THz radiation at room temperature. We observe a maximum signal near to the threshold voltage. This result clearly demonstrates the possibility of plasma wave THz operation of these nanometer scale devices. The response was attributed to a non resonant detection. We also demonstrate the possibility to observe a resonant detection on the same devices.

Field effect transistors for terahertz detection - silicon versus III–V material issue

Resonant frequencies of the two-dimensional plasma in FETs reach the THz range for nanometer transistor channels. Non-linear properties of the electron plasma are responsible for detection of THz radiation with FETs. Resonant excitation of plasma waves with sub-THz and THz radiation was demonstrated for short gate transistors at cryogenic temperatures. At room temperature, plasma oscillations are usually over-damped, but the FETs can still operate as efficient broadband THz detectors. The paper presents the main theoretical and experimental results on detection with FETs stressing their possible THz imaging applications. We discuss advantages and disadvantages of application of III–V GaAs and GaN HEMTs and silicon MOSFETs.

Terahertz Emission and Detection by Plasma Waves in Nanometer Size Field Effect Transistors

Plasma oscillations in nanometer field effect transistors are used for detection and generation of electromagnetic radiation of THz frequency. Following first observations of resonant detection in 150 nm gate length GaAs HEMT, we describe recent observations of room temperature detection in nanometer Si MOSFETs, resonant detection in GaN/AlGaN HEMTs and improvement of room temperature detection in GaAs HEMTs due to the drain current. Experiments on spectrally resolved THz emission are described that involve room and liquid helium temperature emission from nanometer GaInAs and GaN HEMTs.

Asymmetric transmission of transverse magnetic or radially polarized THZ waves through sub-wavelength gratings

We have developed a metallic double circular grating with sub-wavelength slits which blocks radially polarized light incident from one of its sides and acts as a focusing diffractive element in the other direction. The proposed grating has been optimized for the sub-THz frequency range. Unidirectional transmission through the grating has been demonstrated experimentally at 0.1 THz. We have also developed a planar metallic double grating with sub-wavelength slits which blocks light with a transverse magnetic polarization incident from one of the grating sides and transmits radiation incident from the opposite direction into the +1 and -1 diffraction orders. These gratings which could be used as unidirectional couplers consist of optically linear materials and their operation respects the Lorentz reciprocity theorem.

Broadband asymmetric transmission of THz radiation through double metallic gratings

We analyse numerically and experimentally the asymmetric transmission through sub-wavelength double metallic gratings. The possibility of achieving a broadband unidirectional transmission of THz waves through the grating is confirmed. The proposed gratings allow for efficient one-way transmission in the wavelength range from 2.5 to 3.5 mm.

Plasma nonlinearities and terahertz detection by Field Effect Transistors

On overview of recent results concerning the plasma excitations in Field Effect Transistor is presented. We report on high magnetic field studies and we show evidences that the plasma waves are indeed propagating in the transistor channel. We show also how FET based THz detectors parameters can be determined using the static current voltage characteristics. The role of loading effects and temperature to enhance the THz responsivity is also demonstrated.

Spin related effect in Terahertz photovoltaic response of Si-MOSFETs

We report on investigations of photovoltaic response of Si-MOSFETs subjected to Terahertz radiation in high magnetic fields. The MOSFETs develop a dc drain-to-source voltage that shows singularities in magnetic fields corresponding to paramagnetic resonance conditions. These singularities are investigated as a function of incident frequency, temperature and two-dimensional carrier density. We tentatively attribute these resonances to spin transitions of the electrons bounded to Si dopants and discuss the possible physical mechanism of the photovoltaic signal generation.

Plasma waves Terahertz detection by field effect transistor in Quantinzing magnetic fields

Detection of THz radiation by a Field Effect Transistor InGaAs/InAlAs transistor was investigated at 4.2 K as a function of the magnetic field and gate voltage. We observed oscillations of the photovoltaic signal analogous to Shubnikov-de Haas oscillations, as well as their strong enhancement at the cyclotron resonance conditions. The results are successfully quantitatively described within the frame of a recent theory, taking into account a new source of nonlinearity related to Shubnikov-de Haas effect. We show that the detection is due to gated plasmon.

Plasma Wave HEMTs for THz applications

New THz chip solid-state detectors and sources are waited for many applications. The idea of new sources and detectors, based on the oscillations of bidimensional plasma, was theoretically and experimentally demonstrated. We present technological process of nanometric devices dedicated to THz emission. In this structure, a MIM gate-source capacitance is integrated to HEMT to achieve the boundary condition of plasma wave generation and to keep possible the gate biasing, necessary for frequency tuning. High electron mobility material like InAlAs/GalnAs heterostructure is used otherwise the plasma wave is dumped by electron scattering. Electrical and THz measurements are realized.

Plasma wave HEMTs for THz applications

New THz chip solid-state detectors and sources are waited for many applications. The idea of new sources and detectors, based on the oscillations of bidimensional plasma, was theoretically and experimentally demonstrated. We present technological process of nanometric devices dedicated to THz emission. In this structure, a MIM gate-source capacitance is integrated to HEMT to achieve the boundary condition of plasma wave generation and to keep possible the gate biasing, necessary for frequency tuning. High electron mobility material like InAlAs/GalnAs heterostructure is used otherwise the plasma wave is dumped by electron scattering. Electrical and THz measurements are realized.