arXiv subjects

Karuppasamy Pandian Soundarapandian

Publications and source records attributed to Karuppasamy Pandian Soundarapandian.

4 recordsLinked to original sources

arXiv2026

Graphene-enabled coherent (sub-)terahertz wave detection and thickness determination

Phase-sensitive terahertz (THz) detection enables applications ranging from astronomy to non-destructive testing. However, current THz detectors lack phase sensitivity, unless they are combined with external interferometers, or through photomixing. This implies a large footprint and sensitive dependence on alignment. Here, we demonstrate a graphene-enabled, on-chip, integrated (sub-)THz detector-interferometer with optical cavity and antenna, exhibiting high sensitivity to the phase of incident THz light. We exploit this by determining the thickness of thin films placed in front of the detector-interferometer, obtaining a deep sub-wavelength thickness accuracy of a few micrometer, while we predict that an improved accuracy is within reach. This is relevant for a range of industrial application domains, including automotive, construction, and health. We furthermore achieve a record-high external responsivity - considering bias-free graphene-based (sub-)THz detectors - of 172 mA/W and a noise-equivalent power of 26 pW$~\rm{Hz}^{-1/2}$. This performance is due to enhanced absorption at the resonant cavity mode around 89 GHz, in agreement with multi-physics simulations. These results pave the way to exploiting coherent wave detection in the (sub-)THz regime with utility in spectroscopy, next-generation wireless communication, and beyond.

physics.optics↗

arXiv2026

C-band 160 Gbs-1 Zero-bias Graphene Photodetectors: Breaking the Responsivity-Bandwidth Trade-off by Heterostructure Engineering

Graphene photodetectors offer ultrafast response and broadband operation, but their responsivity is typically limited by rapid hot-carrier cooling, leading to a trade-off between sensitivity and speed. Here, we demonstrate that modifying the dielectric environment provides an effective route to control hot-carrier cooling and enhance device performance. By employing a WSe2 encapsulation architecture, we suppress out-of-plane energy dissipation, leading to an increased cooling length (~2.68 um) and a reduced heat-exchange coefficient. As a result, we obtain zero-bias graphene photodetectors with responsivities up to ~0.12 A/W (potentially ~0.4 A/W) while maintaining ultrafast operation beyond the setup-limited 110 GHz bandwidth. The devices enable direct detection at data rates of 120 Gb s-1 (NRZ) and 160 Gb s-1 (PAM-4), with performance achieved using minimal digital signal processing. These results establish dielectric engineering as a key design axis for controlling hot-carrier dynamics, enabling energy-efficient, high-speed optical receivers for next-generation interconnects and AI-driven data systems.

physics.optics↗

arXiv2024

High-Speed Graphene-based Sub-Terahertz Receivers enabling Wireless Communications for 6G and Beyond

In recent years, the telecommunications field has experienced an unparalleled proliferation of wireless data traffic. Innovative solutions are imperative to circumvent the inherent limitations of the current technology, in particular in terms of capacity. Carrier frequencies in the sub-terahertz (sub-THz) range (~0.2-0.3 THz) can deliver increased capacity and low attenuation for short-range wireless applications. Here, we demonstrate a direct, passive and compact sub-THz receiver based on graphene, which outperforms state-of-the-art sub-THz receivers. These graphene-based receivers offer a cost-effective, CMOS-compatible, small-footprint solution that can fulfill the size, weight, and power consumption (SWaP) requirements of 6G technologies. We exploit a sub-THz cavity, comprising an antenna and a back mirror, placed in the vicinity of the graphene channel to overcome the low inherent absorption in graphene and the mismatch between the areas of the photoactive region and the incident radiation, which becomes extreme in the sub-THz range. The graphene receivers achieve a multigigabit per second data rate with a maximum distance of ~3 m from the transmitter, a setup-limited 3 dB bandwidth of 40 GHz, and a high responsivity of 0.16 A/W, enabling applications such as chip-to-chip communication and close proximity device-to-device communication.

physics.optics↗

arXiv2022

Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

High mobility is a crucial requirement for a large variety of electronic device applications. The state-of-the-art for high quality graphene devices is based on heterostructures made with graphene encapsulated in $>80\,$nm-thick flakes of hexagonal boron nitride (hBN). Unfortunately, scaling up multilayer hBN while precisely controlling the number of layers remains an elusive challenge, resulting in a rough material unable to enhance the mobility of graphene. This leads to the pursuit of alternative, scalable materials, which can be simultaneously used as substrate and encapsulant for graphene. Tungsten disulfide (WS$_2$) is a transition metal dichalcogenide, which was successfully grown in large ($\sim$mm-size) multi-layers by chemical vapour deposition. However, the resistance \textit{vs} gate voltage characteristics when gating graphene through WS$_2$ exhibit largely hysteretic shifts of the charge neutrality point (CNP) in the order of $Δn\sim$2.6$\cdot$10$^{11}$ cm$^{-2}$, hindering the use of WS$_2$ as a reliable encapsulant. The hysteresis originates due to the charge traps from sulfur vacancies present in WS$_2$. In this work, we report for the first time the use of WS$_2$ as a substrate and the overcoming of hysteresis issues by chemically treating WS$_2$ with a super-acid, which passivates these vacancies and strips the surface from contaminants. The hysteresis is significantly reduced below the noise level by at least a factor five (to $Δn<$5$\cdot$10$^{10}$ cm$^{-2}$) and, simultaneously, the room-temperature mobility of WS$_2$-encapsulated graphene is as high as $\sim$6.2$\cdot$10$^{4}$ cm$^{-2}$V$^{-1}$s$^{-1}$ at a carrier density $n$ $\sim$1$\cdot$ 10$^{12}$ cm$^{-2}$. Our results promote WS$_2$ to a valid alternative to hBN as encapsulant for high-performance graphene devices.

cond-mat.mes-hall↗