High performance bilayer-graphene Terahertz detectors (1312.3737v1)

Abstract: We report bilayer-graphene field effect transistors operating as THz broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity $\sim 1.2V/W (1.3 mA/W)$ and a noise equivalent power $\sim 2\times 10^{-9} W/Hz^{-1/2}$ in the 0.29-0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.

Overview of Bilayer-Graphene Terahertz Detectors

This paper presents significant advancements in terahertz (THz) broadband photodetection through the utilization of bilayer-graphene field effect transistors (BLG-FETs). By exploring the plasma-wave excitation in such devices, the authors achieve enhanced responsivity and minimized noise equivalent power (NEP) compared to existing technologies. These detectors were shown to operate efficiently in the 0.29-0.38 THz range at room temperature, in both photovoltage and photocurrent modes, highlighting the potential for scalable applications in higher frequency detection systems and flexible device configurations.

Key Technical Contributions

• Device Architecture: Two primary configurations were employed: devices with large gate lengths (1 µm) and buried gate geometries. The bilayer graphene was selected as the material for the FETs due to its superior modulation of carrier density, which has been found more effective in bilayer than single-layer graphene for achieving higher responsivity at THz frequencies.
• Experimental Setup and Findings: The experiments were conducted using mechanically exfoliated bilayer graphene flakes on silicon substrates. The devices obtained were characterized both electrically and optically, revealing a consistent shift in the channel neutrality point upon THz radiation exposure. Maximum responsivities of 1.2 V/W and 1.3 mA/W were achieved, complemented by NEP as low as 2×10^-9 W√Hz.

Analysis and Results

The unique configuration of the BLG-FETs led to the excitation of overdamped plasma waves, enabling broadband THz detection. This mechanism was confirmed by the frequency-independence of the detector's response, validating its potential for various high-frequency and tunable applications. The observed responsivity was significantly higher than those reported in prior studies, attributed to optimized gating and efficient radiation coupling, which minimizes competing thermoelectric effects and negates observable interband transitions.

Implications and Future Directions

This research points towards impactful applications in strategic fields such as biomedical diagnostics, environmental monitoring, and security due to the non-ionizing nature of THz radiation, which allows penetration through conventional dielectrics. The increased responsivity and performance metrics of the BLG-FETs indicate that these devices could readily be employed in commercial THz detection systems. Future research may explore expanded tunability in THz ranges, further integration into flexible and large-area architectures, and advances in material sciences to push these devices beyond current performance limits for more demanding applications.

In summary, this paper provides a intellectually rigorous investigation into BLG-FETs for THz detection, bridging critical gaps in solid-state detector technologies and opening pathways for novel device integrations in numerous practical domains.