Engineering the Photodetection, Strain and Neuromorphic Performance of 2D-TMD Transistors

In recent years, researchers have leveraged the unique physical properties of layered two-dimensional (2D) van der Waals (vdW) materials, such as a wide range of thickness-dependent bandgaps and facile fabrication of heterostructures with defect-free heterointerfaces, for several electronic and optoelectronic applications. At the same time, their optical and electrical properties can be controlled using strain tuning of band structure parameters because of their high tensile strength, as well as via electrostatic gating-based tuning of carrier concentrations because of their ultra-thin nature.<br/><br/>The first part of the presentation will cover results on engineering photo-detection of transistors based on 2D vdW transition metal dichalcogenide (TMD) semiconductors and their heterostructures. Photoresponsivity and speed of few-layer TMD photodetectors are fundamentally traded-off with each other by modulation of the effective trap concentration, as shown through electrostatically gated supported and suspended ReS₂ photodetectors.[1] This trade-off can be attenuated by nearly 2× using an electrostatically tunable in-plane p-n homojunction integrated laterally with a WSe₂ phototransistor, enabling enhanced photoresponsivity (&gt;100 A/W), and high detectivity (&gt;10¹² Jones) along with switching speed in the ms range at the same time.[2] Beyond single-TMD photodetection, TMD/TMD heterostructures offer the possibilities of interlayer interface engineering for improving photodetection parameters. For instance, engineering the band alignment from type-II to type-III in a WSe₂/SnSe₂ p-n heterodiode helps realize a high negative responsivity of 2 × 10⁴ A/W with a fast response time of ~1 ms due to a tunneling photocurrent.[3]<br/><br/>The next part will describe the strain-modulated performance of 2D-TMD transistors, wherein an electrically actuated piezo-stack is employed to fine-tune optical and electrical parameters of MoS₂ field-effect transistors with tensile as well as compressive strain, offering improved control and integration possibilities over existing mechanical methods.[4] Finally, we will describe the use of independent electrostatic gating of contact and channel barriers in 2D TMD transistors towards realizing neuronal spiking behaviour, closely mimicking biological neurons with functionalities such as spike-frequency adaptation and post-inhibitory rebound, at a low energy consumption of 3.5 pJ/spike.[5]<br/><br/><b>References</b><br/>[1] K. Thakar, B. Mukherjee, S. Grover, N. Kaushik, M. Deshmukh, S. Lodha, ACS Applied Materials and Interfaces, 10, 42, 36512 (2018).<br/>[2] S. Ghosh, A. Varghese, K. Thakar, S. Dhara, S. Lodha, Nature Communications, 12, 3336 (2021).<br/>[3] S. Ghosh, A. Varghese, H. Jawa, Y. Yin, N. V. Medhekar, S. Lodha, ACS Nano, 16, 4578−4587 (2022).<br/>[4] A. Varghese, A. Pandey, P. Sharma, Y. Yin, N. Medhekar, S. Lodha, to appear in Nano Letters (2024).<br/>[5] K. Thakar, B. Rajendran, S. Lodha, npj 2D Materials and Applications, 7 (68), 2023.