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Probing interlayer excitons in a vertical van der Waals p-n junction using scanning probe microscopy technique
摘要： Two dimensional (2D) semiconductors feature exceptional optoelectronic properties controlled by strong confinement in one dimension. In this contribution, we studied interlayer excitons in a vertical p-n junction made of bilayer n-type MoS2 and few layers of p-type GaSe using current sensing atomic force microscopy (CSAFM). The p-n interface is prepared by mechanical exfoliation onto highly ordered pyrolytic graphite (HOPG). Thus the heterostructure creates an ideal layered system with HOPG serving as the bottom contact for the electrical characterization. Home-built Au tips are used as the top contact in CSAFM mode. During the basic diode characterization, the p-n interface shows strong rectification behavior with a rectification ratio of 104 at ±1 V. The I-V characteristics reveal pronounced photovoltaic effects with a fill factor of 0.55 by an excitation below the band gap. This phenomenon can be explained by the dissociation of interlayer excitons at the interface. The possibility of the interlayer exciton formation is indicated by density functional theory (DFT) calculations on this heterostructure: the valence band of GaSe and the conduction band of MoS2 contribute to an interface-specific state at an energy of about 1.5 eV. The proof of excitonic transitions to that state is provided by photoluminescence measurements at the p-n interface. Finally, photocurrent mapping at the interface under an excitation wavelength of 785 nm provides evidence of efficient extraction of such excitons. Our results demonstrate a pathway towards a two dimensional device for future optoelectronics and light harvesting assisted by interlayer excitons in a van der Waals heterostructure.
关键词： optoelectronics,van der Waals heterojunction,GaSe,density functional theory,MoS2,interlayer exciton,p-n junction
更新于2025-09-23 15:23:52
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MoS2/silicon-on-insulator Heterojunction Field-Effect-Transistor for High-performance Photodetection
摘要： In this letter, we demonstrate a novel junction field effect transistor (JFET) by transferring MoS2 onto silicon-on-insulator (SOI) substrate to control the thin Si channel. By combining high light absorption coefficient in MoS2 with high internal gain in thin Si channel, the device can be used for photodetection and achieve high responsivity up to ~1.78×104 A/W, high detectivity over 3×1013 Jones, and short response time down to 1.44 ms. Furthermore, unlike conventional SOI photodetector which is only sensitive to UV light, the response spectrum of our proposed device peaks in visible/near-infrared region, which is interesting for imaging and optical communication applications.
关键词： SOI,High photoresponsivity,Van der Waals heterojunction,MoS2,Junction field effect transistor
更新于2025-09-23 15:22:29
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Hexagonal Boron Nitride for Surface Passivation of Two-dimensional van der Waals Heterojunction Solar Cells
摘要： Two-dimensional (2D) semiconductors can be promising active materials for solar cells due to their advantageous electrical and optical properties, in addition to their ability to form high-quality van der Waals (vdW) heterojunctions using a simple process. Furthermore, the atomically thin nature of these 2D materials allows them to achieve light-weighted and transparent thin-film solar cells. However, strategies appropriate for optimizing their properties have not been extensively studied yet. In this paper, we propose a method for reducing the electrical loss of 2D vdW solar cells by introducing hexagonal boron nitride (h-BN) as a surface passivation layer. This method allowed us to enhance the photovoltaic performance of a MoS2/WSe2 solar cell. In particular, we observed ~74 % improvement of the power conversion efficiency owing to a large increase in both short-circuit current and open-circuit voltage. Such a remarkable performance enhancement was due to the reduction of the recombination rate at the junction and surface of non-overlapped semiconductor regions, which was confirmed via time-resolved photoluminescence analysis. Furthermore, the h-BN top layer was found to improve the long-term stability of the tested 2D solar cell under ambient conditions. We observed the evolution of our MoS2/WSe2 solar cell for a month and found that h-BN passivation effectively suppressed its degradation speed. In particular, the degradation speed of the passivated cell was twice as low as that of a non-passivated cell. This work reveals that h-BN can successfully suppress the electrical loss and degradation of 2D vdW heterojunction solar cells under ambient conditions.
关键词： surface passivation,solar cell,MoS2,WSe2,2D material,van der Waals heterojunction,h-BN
更新于2025-09-16 10:30:52
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Integration of MoS <sub/>2</sub> with InAlAs/InGaAs Heterojunction for Dual Color Detection in Both Visible and Near‐Infrared Bands
摘要： At present, dual-channel or even multi-channel recording is a developing trend in the field of photodetection, which is widely applied in environment protection, security, and space science and technology. This paper proposes a novel MoS2/InAlAs/InGaAs n–i–n heterojunction phototransistor by integrating multi-layered MoS2 with InGaAs-based high electron mobility transistors (InGaAs-HEMTs). Due to the internal photocurrent amplification in the InGaAs channels with a narrow energy bandgap of 0.79 eV, this device exhibits high photoresponsivity (R) of over 8 × 105 A W–1 under near-infrared illumination of 1550 nm at 500 pW. Furthermore, with the combination of the photoconductance effect in the vertical MoS2/InAlAs/InGaAs n–i–n heterojunction and the photogating effect in the lateral phototransistor, this device possesses a unique characteristic under visible illumination that its photoresponsivity can be tuned by the top gate electrode from 6 × 105 A W–1 to -4 × 105 A W–1 by gate voltage. This may lead to a new application as an optically controlled electronic inverter, which needs further study in depth. This MoS2/InAlAs/InGaAs phototransistor builds up a new bridge between 2D materials and conventional ternary compounded semiconductor devices.
关键词： MoS2/InAlAs/InGaAs van der Waals heterojunction,gate-tunable negative/positive responsivity,dual-band photodetection,2D electron gas
更新于2025-09-11 14:15:04