Two-dimensional layered semiconductors such as MoS₂ and WSe₂ have attracted considerable interest in recent times. Exploring the full potential of these layered materials requires precise spatial modulation of their chemical composition and electronic properties to create well-defined heterostructures. Here, we report the growth of compositionally modulated MoS₂-MoSe₂ and WS₂-WSe₂ lateral heterostructures by in situ modulation of the vapour-phase reactants during growth of these two-dimensional crystals. Raman and photoluminescence mapping studies demonstrate that the resulting heterostructure nanosheets exhibit clear structural and optical modulation. Transmission electron microscopy and elemental mapping studies reveal a single crystalline structure with opposite modulation of sulphur and selenium distributions across the heterostructure interface. Electrical transport studies demonstrate that the WSe₂-WS₂ heterojunctions form lateral p-n diodes and photodiodes, and can be used to create complementary inverters with high voltage gain. Our study is an important advance in the development of layered semiconductor heterostructures, an essential step towards achieving functional electronics and optoelectronics.
Band gap engineering of atomically thin two-dimensional layered materials is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here we report, for the first time, a simple one-step chemical vapor deposition approach for the simultaneous growth of alloy MoS2xSe2(1-x) triangular nanosheets with complete composition tunability. Both the Raman and the photoluminescence studies show tunable optical properties consistent with composition of the alloy nanosheets. Importantly, all samples show a single bandedge emission peak, with the spectral peak position shifting from 668 nm (for pure MoS2) to 795 nm (for pure MoSe2), indicating the high quality for these complete composition alloy nanosheets. These band gap engineered 2D structures could open up an exciting opportunity for probing their fundamental physical properties in 2D and may find diverse applications in functional electronic/optoelectronic devices.
Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently emerged as a new class of atomically thin semiconductors for diverse electronic, optoelectronic, and valleytronic applications. To explore the full potential of these 2D semiconductors requires a precise control of their band gap and electronic properties, which represents a significant challenge in 2D material systems. Here we demonstrate a systematic control of the electronic properties of 2D-TMDs by creating mixed alloys of the intrinsically p-type WSe2 and intrinsically n-type WS2 with variable alloy compositions. We show that a series of WS2xSe2-2x alloy nanosheets can be synthesized with fully tunable chemical compositions and optical properties. Electrical transport studies using back-gated field effect transistors demonstrate that charge carrier types and threshold voltages of the alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. A highly p-type behavior is observed in selenium-rich alloy, which gradually shifts to lightly p-type, and then switches to lightly n-type characteristics with the increasing sulfur atomic ratio, and eventually evolves into highly n-doped semiconductors in sulfur-rich alloys. The synthesis of WS2xSe2-2x nanosheets with tunable optical and electronic properties represents a critical step toward rational design of 2D electronics with tailored spectral responses and device characteristics.
Although great efforts have been devoted to the synthesis of halide perovskites nanostructures, vapor growth of high-quality one-dimensional cesium lead halide nanostructures for tunable nanoscale lasers is still a challenge. Here, we report the growth of high-quality all-inorganic cesium lead halide alloy perovskite micro/nanorods with complete composition tuning by vapor-phase deposition. The as-grown micro/nanorods are single-crystalline with a triangular cross section and show strong photoluminescence which can be tuned from 415 to 673 nm by varying the halide composition. Furthermore, these single-crystalline perovskite micro/nanorods themselves function as effective Fabry-Perot cavities for nanoscale lasers. We have realized room-temperature tunable lasing of cesium lead halide perovskite with low lasing thresholds (∼14.1 μJ cm) and high Q factors (∼3500).
Cesium lead halide perovskite nanowires have emerged as promising low-dimensional semiconductor structures for integrated photonic applications. Understanding light-matter interactions in a nanowire cavity is of both fundamental and practical interest in designing low-power-consumption nanoscale light sources. In this work, high-quality in-plane aligned halide perovskite CsPbX (X = Cl, Br, I) nanowires are synthesized by a vapor growth method on an annealed M-plane sapphire substrate. Large-area nanowire laser arrays have been achieved based on the as-grown aligned CsPbX nanowires at room temperature with quite low pumping thresholds, very high quality factors, and a high degree of linear polarization. More importantly, it is found that exciton-polaritons are formed in the nanowires under the excitation of a pulsed laser, indicating a strong exciton-photon coupling in the optical microcavities made of cesium lead halide perovskites. The coupling strength in these CsPbX nanowires is dependent on the atomic composition, where the obtained room-temperature Rabi splitting energy is ∼210 ± 13, 146 ± 9, and 103 ± 5 meV for the CsPbCl, CsPbBr, and CsPbI nanowires, respectively. This work provides fundamental insights for the practical applications of all-inorganic perovskite CsPbX nanowires in designing light-emitting devices and integrated nanophotonic systems.
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