Abstract-Line-defect photonic crystal terahertz quantum cascade laser

Journal of Applied Physics

A. Klimont, A. Ottomaniello,  R. Degl’Innocenti, L. Masini, F. Bianco, Y. Wu1,  Y. D. Shah, Y. Ren, D. S. Jessop,  A. Tredicucci, H. E. Beere,  D. A. Ritchie.

Scanning electron microscope (SEM) pictures of the line defect QCLs after reactive ion etching for three different line-defect waveguides. Figure (a) corresponds to D1, where the defects before BCB planarization are separated by one row of small pillars in the triangular PhC lattice. Figure (b) (D3) and (c) (D5) correspond to line-defect QCLs separated by three rows and five rows of small pillars, respectively. Figure (d) shows in more detail the defect area and identifies the main parameters of the PhC structure, such as the vectors on the direct triangular lattice, a1 and a2, the radius of the regular and defect pillars, r and R, respectively, as well as the line orientation. Figure (e) shows a typical line-defect QCL after the BCB planarization, leaving only the tops of ∼14 μm-tall pillars exposed.

https://aip.scitation.org/doi/full/10.1063/1.5120025

The terahertz (THz) quantum cascade laser (QCL) provides a versatile tool in a plethora of applications ranging from spectroscopy to astronomy and communications. In many of these fields, compactness, single mode frequency emission, and low threshold are highly desirable. The proposed approach, based on line defects in a photonic crystal (PhC) matrix, addresses all these features while offering unprecedented capabilities in terms of flexibility, light waveguiding, and emission directionality. Nine line-defect QCLs were realized in a triangular lattice of pillars fabricated in the laser active region (AR), centered around ∼2 THz by tuning the photonic design. A maximal 36% threshold reduction was recorded for these ultraflat dispersion line-defect QCLs in comparison to standard metal-metal QCL. The mode selectivity is an intrinsic property of the chosen fabrication design and has been achieved by lithographically scaling the dimension of the defect pillars and by acting on the PhC parameters in order to match the AR emission bandwidth. The measured line-defect QCLs emitted preferentially in the single frequency mode in the propagation direction throughout the entire dynamic range. An integrated active platform with multiple directional outputs was also fabricated as proof-of-principle to demonstrate the potential of this approach. The presented results pave the way for integrated circuitry operating in the THz regime and for fundamental studies on microcavity lasers.

Abstract-Terahertz detection by epitaxial-graphene field-effect-transistors on silicon carbide

F. Bianco^1,a), D. Perenzoni², D. Convertino³, S. L. De Bonis^1,b), D. Spirito^1,c),M. Perenzoni², C. Coletti³, M. S. Vitiello¹ and A. Tredicucci^2,4
 HIDE AFFILIATIONS
1 NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
2 Fondazione Bruno Kessler (FBK), Via Sommarive 18, 38123 Povo, Trento, Italy
3 CNI@NEST, Istituto Italiano di Tecnologia, Piazza S. Silvestro 12, 56127 Pisa, Italy
4 NEST, Istituto Nanoscienze-CNR and Dipartimento di Fisica “E. Fermi”, Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
a) Author to whom correspondence should be addressed. Electronic mail: federicabianco82@gmail.com
b) Present address: ICFO, Av. Carl Friedrich Gauss, Centre d'Investigació en Nanociència, Castelldefels, Barcelona 08860, Spain.
c) Present address: Istituto Italiano di Tecnologia, Nanochemistry department and Graphene labs, Via Morego 30, 16163 Genova, Italy.
Appl. Phys. Lett. 107, 131104 (2015); http://dx.doi.org/10.1063/1.4932091

http://scitation.aip.org/content/aip/journal/apl/107/13/10.1063/1.4932091?TRACK=RSS

We report on room temperature detection of terahertz radiation by means of antenna-coupledfield effect transistors (FETs) fabricated using epitaxial graphene grown on silicon carbide. The achieved photoresponsivity (∼0.25 V/W) and noise equivalent power (∼80 nW/ Hz−−−√ ) result from the combined effect of two independent detection mechanisms: over-damped plasma wave rectification and thermoelectric effects, the latter ascribed to the presence of carrier density junctions along the FET channel. The calculated plasmonic and thermoelectric response reproduces qualitatively well the measured photovoltages; the experimentally observed sign-switch demonstrates the stronger contribution of plasmonic detection compared to the thermoelectric one. These results unveil the potential of plasmonic detectors exploitingepitaxial graphene on silicon carbide for fast large area imaging of macroscopic samples.