WS₂ Nanosheet/Si p–n Heterojunction Diodes for UV–Visible Broadband Photodetection

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).

Enhanced photodetection and a wider spectral range in the In2S3–ZnO 2D–3D heterojunction: combined optical absorption and enhanced carrier separation at the type-II heterojunction

“…The n–n heterojunction has a distinct band alignment for photogenerated charge carriers, which shows an energy barrier at the interface and leads to more separation and a lesser recombination of photogenerated charge carriers for type-II heterojunction samples, resulting in an enhancement of the current density at the 2D–3D interface. 43…”

Self‐Powered Photodetector Based on p‐Type CuBi2O4 with Fermi Level Engineering

“…As shown in Figure 1c, all peaks align strongly to those of the CBO film and Si substrate: four distinct vibrational peaks at 132, 264, 407, and 585 cm −1 correspond to the presence of CBO, and the peaks at 302 and 520 cm −1 correspond to Si substrate. [ 25,35 ]…”

“…202101443 Surface passivation or constructing heterostructure contacts are common strategies to overcome the drawback of leakage current in Si-based PDs. [22][23][24][25][26][27] Fang et al designed PDs with improved photoresponse and suppressed leakage current by chemically regrowing the interfacial SiO x layer and depositing a Ti 3 C 2 MXene layer on the surface of the Si. [28] Kang et al built a schematic layer structure for fused InGaAs/Si devices allowed for a low dark current and an improved signal-tonoise ratio for the device through built-in electric field.…”

“…As shown in Figure 1c, all peaks align strongly to those of the CBO film and Si substrate: four distinct vibrational peaks at 132, 264, 407, and 585 cm −1 correspond to the presence of CBO, and the peaks at 302 and 520 cm −1 correspond to Si substrate. [25,35] The crystalline structure of the CBO film is characterized by X-ray diffraction (XRD) patterns, Figure 1e. The diffraction peaks located at 20.9°, 28.2°, 33.5°, 37.6°, 47.0°, 53.3°, and 55.9° correspond to the (200), ( 211), (310), ( 202), ( 411), (213), and (332) crystal planes of CBO (JCPDS, 42-0334), respectively.…”

“…Additionally, metal oxide semiconductors are stable and easy to prepare and process, making them ideal for assembling high-performance PDs on a large scale. [15,25] So far, many metal oxide semiconductors like TiO 2 , ZnO, and GaN, have been used as the functional overlayer for Si based PDs. However, limited by the n-type conduction properties, they failed to match the demands of n-type substrate semiconductors.…”