Stephane Boubanga-Tombet

InP- and GaAs-Based Plasmonic High-Electron-Mobility Transistors for Room-Temperature Ultrahigh-Sensitive Terahertz Sensing and Imaging

This paper reviews recent advances in the design and performance of our original InP- and GaAs-based plasmonic high-electron-mobility transistors (HEMTs) for ultrahighly-sensitive terahertz (THz) sensing and imaging. First, the fundamental theory of plasmonic THz detection is briefly described. Second, single-gate HEMTs with parasitic antennae are introduced as a basic core device structure, and their detection characteristics and sub-THz imaging potentialities are investigated. Third, dual-grating-gate (DGG)-HEMT structures are investigated for broadband highly sensitive detection of THz radiations, and the record sensitivity and the highly-sensitive THz imaging are demonstrated using the InP-based asymmetric DGG-HEMTs. Finally, the obtained results are summarized and future trends are addressed.

Current-driven detection of terahertz radiation using a dual-grating-gate plasmonic detector

We report on the detection of terahertz radiation by an on-chip planar asymmetric plasmonic structure in the frequency region above one terahertz. The detector is based on a field-effect transistor that has a dual grating gate structure with an asymmetric unit cell, which provides a geometrical asymmetry within the structure. Biasing the detector with a dc source-to-drain current in the linear region of the current-voltage characteristic introduces an additional asymmetry (electrical asymmetry) that enhances the detector responsivity by more than one order of magnitude (by a factor of 20) as compared with the unbiased case due to the cooperative effect of the geometrical and electrical asymmetries. In addition to the responsivity enhancement, we report a relatively low noise equivalent power and a peculiar non-monotonic dependence of the responsivity on the frequency, which results from the multi-plasmonic-cavity structure of the device.

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.

Ultrahigh sensitive plasmonic terahertz detectors based on an asymmetric dual-grating gate HEMT structure

We report on ultrahigh sensitive, broadband terahertz (THz) detectors based on asymmetric double-grating-gate (A-DGG) high electron mobility transistors, demonstrating a record responsivity of 2.2 kV/W at 1 THz with a superior low noise equivalent power of 15 pW/√Hz using InGaAs/InAlAs/InP material systems. When THz radiation is absorbed strong THz photocurrent is first generated by the nonlinearity of the plasmon modes resonantly excited in undepleted portions of the 2D electron channel under the high-biased sub-grating of the A-DGG, then the THz photovoltaic response is read out at high-impedance parts of 2D channel under the other sub-grating biased at the level close to the threshold. Extraordinary enhancement by more than two orders of magnitude of the responsivity is verified with respect to that for a symmetric DGG structure.

Helicity sensitive terahertz radiation detection by dual-grating-gate high electron mobility transistors

We report on the observation of a radiation helicity sensitive photocurrent excited by terahertz (THz) radiation in dual-grating-gate (DGG) InAlAs/InGaAs/InAlAs/InP high electron mobility transistors (HEMT). For a circular polarization the current measured between source and drain contacts changes its sign with the inversion of the radiation helicity. For elliptically polarized radiation the total current is described by superposition of the Stokes parameters with different weights. Moreover, by variation of gate voltages applied to individual gratings the photocurrent can be defined either by the Stokes parameter defining the radiation helicity or those for linear polarization. We show that artificial non-centrosymmetric microperiodic structures with a two-dimensional electron system excited by THz radiation exhibit a dc photocurrent caused by the combined action of a spatially periodic in-plane potential and spatially modulated light. The results provide a proof of principle for the application of DGG HEMT for all-electric detection of the radiations polarization state.

Recent advances in the research toward graphene-based terahertz lasers

This paper reviews recent advances in the research and development toward the graphene-based terahertz (THz) lasers. Mass-less Dirac Fermions of electrons and holes in gapless and linear symmetric band structures in graphene enable a gain in a wide THz frequency range under optical or electrical pumping. The excitation of the surface plasmon polaritons in the population-inverted graphene dramatically enhances the THz gain. Photon-emission-assisted resonant tunneling in a double-graphene-layered nano-capacitor structure also strongly enhances the THz gain. Novel graphene-based heterostructures using these physical mechanisms for the current-injection driven THz lasing are discussed. Their superior gain-spectral properties are analyzed and the laser cavity structures for the graphene THz laser implementation are discussed.

Coherent and tunable terahertz emission from nano-metric field effect transistor at room temperature

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. Our results shows that properly exciting nanotransistors can pave the way for new class of coherent and easily tunable THz sources.