Systèmes électroniques bidimensionnels dans des nano-hétérostructures de semi-conducteurs comme sources de rayonnement térahertz

This paper reviews recent advances in emission of terahertz radiation from two-dimensional (2D) electron systems in semiconductor nano-heterostructures. 2D plasmon resonance is first presented to demonstrate intense broadband terahertz emission from InGaP/InGaAs/GaAs material systems. The device structure is based on a high-electron mobility transistor and incorporates the author's original interdigitated dual-grating gates. Second topic focuses on graphene, a monolayer carbon-atomic honeycomb lattice crystal, exhibiting unique carrier transport and optical properties owing to massless and gapless energy spectrum. Coherent stimulated terahertz emission from femtosecond infrared-laser pumped epitaxial graphene is experimentally observed, reflecting the occurrence of negative dynamic conductivity and population inversion

Effects of valence fluctuation and pseudogap formation on phonon thermal conductivity of Ce-based compounds with ε-TiNiSi-type structure

We have measured the thermal conductivity of isostructural compounds CePtSn, CeNiSn, CeRhSb, and CeRhAs with the orthorhombic ε-TiNiSi-type structure. It is found that the phonon thermal conductivity is reduced in a systematic way with increasing Kondo temperature TK. The scattering of phonons by valence fluctuations should play a dominant role in such a reduction. The gap formation in the electronic density of states enhances the phonon thermal conductivity significantly in CeRhAs with a gap width of 280 K, while it is weak in CeNiSn or CeRhSb with a pseudogap of 20-30 K. A phenomenological model is proposed for the unusual temperature dependence of phonon thermal conductivity by taking account of the strong dependence of the electron-phonon scattering rate on both TK and the energy gap

Improved stability in wide-recess InP HEMTs by means of a fully passivated two-step-recess gate

We report two-step-recess gate InP HEMTs with a new process option suitable for producing a wide recess. In the new devices the gate recess is completely covered with a passivation film. Though the gate recess is extremely wide, a transconductance of 1S/mm and a cutoff frequency of 208GHz are achieved with 100-nm gate devices. Moreover, a huge improvement in the drain reliability is achieved by the wide recess which reduces hot-carrier-induced degradation, and by the full passivation which eliminates the instability related to the recess surface