Deepika Yadav

Terahertz wave generation and detection in double-graphene layered van der Waals heterostructures

We report on the first experimental observation of terahertz emission and detection in a double graphene layered (GL) heterostructure which comprises a thin hexagonal-boron nitride tunnel-barrier layer sandwiched between two separately contacted GLs. Inter-GL population inversion is induced by electrically biasing the structure. Resonant tunneling and negative differential resistance is expected when the two graphene band structures are perfectly aligned. However, in the case of small misalignments we demonstrate that the photon-absorption/emission-assisted non-resonant- and resonant-tunneling causes all excess charges in the n-type GL to recombine with the holes in the p-type GL giving rise to an increased measured dc current. This work highlights a novel strategy for the realization of efficient voltage-tunable terahertz emitters and detectors.

Terahertz light-emitting graphene-channel transistor toward single-mode lasing

Abstract A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabricated as a current-injection terahertz (THz) light-emitting laser transistor. We observed a broadband emission in a 1–7.6-THz range with a maximum radiation power of ~10 μW as well as a single-mode emission at 5.2 THz with a radiation power of ~0.1 μW both at 100 K when the carrier injection stays between the lower cutoff and upper cutoff threshold levels. The device also exhibited peculiar nonlinear threshold-like behavior with respect to the current-injection level. The LED-like broadband emission is interpreted as an amplified spontaneous THz emission being transcended to a single-mode lasing. Design constraints on waveguide structures for better THz photon field confinement with higher gain overlapping as well as DFB cavity structures with higher Q factors are also addressed towards intense, single-mode continuous wave THz lasing at room temperature.

Terahertz LED based on current injection dual-gate graphene-channel field effect transistors

Previous studies have shown that optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers and light-emitting devices [1-4]. Recently we obtained preliminary results of single-mode THz lasing in a forward-biased graphene structure with a lateral p-i-n junction in a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) [5]. In this work, we experimentally observe amplified spontaneous broadband THz emission from 1 to 7.6 THz at 100K by carrier-injection in a population-inverted DFB-DG-GFET, demonstrating the birth of a new type of THz light-emitting diodes.

Graphene-based van der Waals heterostructures for emission and detection of terahertz radiation

This paper reviews recent advances in the research of graphene-based van der Waals heterostructures for emission and detection of terahertz radiation. A gated double-graphene-layer (DGL) nanocapacitor is the core shell under consideration, in which a thin tunnel barrier layer is sandwiched by outer graphene layers at both sides. The DGL can support symmetric optical and anti-symmetric acoustic coupled plasmon modes in the GLs. The latter mode can modulate the band-offset between the GL, giving rise to modulation of the inter-GL-layer resonant tunneling. This can dramatically enhance the THz gain or responsivity via plasmon-assisted inter-GL resonant tunneling.

Terahertz emitters and detectors based on double-graphene-layer van der Waals heterostructures

Summary form only given. Double-graphene-layer (DGL) heterostructures have recently attracted much attention due to their potential applications in high speed modulators of terahertz (THz) and infrared (IR) radiation, transistors, and THz photomixers. In this work we report experimental observation of THz emission and detection in the DGL device structures. We demonstrate that the photon-assisted resonant radiative inter-GL transitions enable the applications of such devices for THz/IR lasers and photodetectors (PDs).The main element of both the lasers and PDs under consideration is a D-GL heterostructure with the independently contacted GLs (in red) separated by the thin transparent tunnel-barrier layer. The bias voltage V applied between the GLs contacts induces the electron and hole gases in the opposing GLs. The electron and hole densities in GLs are also controlled by the gate voltage Vg. SEM image of the fabricated devices were shown where the metal contact connected to the upper and lower graphene sheets can be seen as well as the active area of devices (700 nm × 1500 nm). The voltage-dependent band-offset energy between the Dirac points of the GLs and the depolarization shift determine the energies of the photons emitted (in the lasers) or absorbed (in the PDs) in the resonant-tunneling inter-GL transitions. The tunneling causes all excess charges in the n-type GL to recombine with the holes in the p-type GL. The inter-GL radiative C-C and V-V transitions in D-GL laser were shown.