D. Coquillat

Ultrahigh sensitive sub-terahertz detection by InP-based asymmetric dual-grating-gate high-electron-mobility transistors and their broadband characteristics

We report on room-temperature plasmonic detection of sub-terahertz radiation by InAlAs/InGaAs/InP high electron mobility transistors with an asymmetric dual-grating-gate structure. Maximum responsivities of 22.7 kV/W at 200 GHz and 21.5 kV/W at 292 GHz were achieved under unbiased drain-to-source condition. The minimum noise equivalent power was estimated to be 0.48 pW/Hz0.5 at 200 GHz at room temperature, which is the record-breaking value ever reported for plasmonic THz detectors. Frequency dependence of the responsivity in the frequency range of 0.2–2 THz is in good agreement with the theory.

AlGaN/GaN HEMT’s photoresponse to high intensity THz radiation

Abstract We report on the photoresponse dependence on the terahertz radiation intensity in ALGaN/GaN HEMTs. We show that the ALGaN/GaN HEMT can be used as a THz detector in CW and in pulsed regime up to radiation intensity of several kW/cm2. The dynamic range in the pulsed regime of detection can be more than 2 decades. We observed that the photoresponse of the HEMT could have a compound composition if two independent parts of the transistor are involved in the detection process; this result indicates that a more simple one channel device may be preferable on the detection purpose.

Arrays of selectively grown GaN micro-pyramids: photonic and optical-frequency phonon properties

An array of GaN micro-pyramids containing a near-surface InxGa1-xN/GaN single quantum well has been fabricated using selective area epitaxial overgrowth above a patterned silica mask. The pyramid array has been studied by means of angle-resolved reflection measurements in the near- and mid- infrared optical ranges. We have found that the periodic array of flat-topped pyramids shows marked resonances in the near-infrared optical range due to resonant Bloch modes within the extraction cone and that the angular dispersion of these modes exhibits strong photonic crystal characteristics. The experimental results are in good agreement with the photonic band structure calculated using a scattering matrix formalism. The mid-infrared optical anisotropy properties of the micro-pyramids were investigated to probe the infrared active phonons of the pyramid array. The A1(LO) phonon of the InxGa1-xN/GaN single quantum well was identified and the InN mole fraction was estimated from the mode behaviour.

Enhancement of second harmonic generation due to quasi-phase matching condition in a GaN-based one-dimensional photonic crystal

This paper reports measurements of the the giant second harmonic generation (SHG) enhancement of a 1D thin-film GaN-based photonic structure. The extraordinary enhancement has been obtained in specular reflection when the angular configuration satisfies the quasi-phase-matching (QPM) conditions, i.e. when both the fundamental and SH fields are resonant with radiative Bloch modes.

Equifrequency surfaces in a two-dimensional GaN photonic crystal for second-harmonic generation with tuning range

The equifrequency surface plot is demonstrated as a powerful tool in obtaining the angular geometries that maintain quasi-phase matched (QPM) conditions for enhanced SHG with extended tuning range. These results are promising for the practical realisation of nonlinear frequency conversion devices based on GaN and related materials.