WS<sub>2</sub> Nanosheet/Si p–n Heterojunction Diodes for UV–Visible Broadband Photodetection
Suparna Pal, Subhrajit Mukherjee, Ravindra Jangir, Mangla Nand, Dipankar Jana, S.K. Mandal, S. Bhunia, C. Mukherjee, S. N. Jha, S. K. Ray
Abstract
High-quality, continuous transition-metal dichalcogenide (TMD) thin films with large-area coverage are the prerequisites for practical device applications. To address the growing demand, here we report high photoresponse and high detectivity of WS2 nanosheet/Si p–n heterojunction diodes for potential application in UV–visible broadband photodetection based on the wafer-scale deposition of WS2 nanosheets. Monolayer equivalent efficiency, i.e., high responsivity and high detectivity, has been achieved in these devices utilizing its nanotextured morphology. Nanotexturization in the surface morphology increased the effective area for absorption as well as contributed to quantization, leading to superior device performance. RF sputtering followed by high-temperature annealing in the sulfur-rich environment has been adopted to achieve stoichiometric WS2 films with high crystalline quality. The valence band offset for the WS2/Si heterointerface has been determined to be 0.48 ± 0.2 eV, for the band alignment of heterojunction devices. The fabricated n-WS2/p-Si junction diode displayed excellent rectifying characteristics (rectification ratio of ∼630) with a low leakage current (∼1 × 10–7 A). The photodiode exhibits a superior photo-to-dark current ratio (∼1200) and very high photoresponsivity (>4 A/W) under the reverse bias condition. Moreover, a high detectivity of ∼4.8 × 1012 Jones with a linear dynamic range (LDR) of 62 dB at −3 V has also been achieved. A reasonably fast response time, of approximately a few milliseconds of the fabricated photodiode, has made them excellent candidates for large-area photodetectors, operational for the broadband spectral range (300–800 nm).