The advent of low-dimensional materials with peculiar structure and superb band properties provides a new canonical form for the development of photodetectors. However, the limited exploitation of basic properties makes it difficult for devices to stand out. Here, we demonstrate a hybrid heterostructure with ultrathin vanadium dioxide film and molybdenum ditelluride nanoflake. Vanadium dioxide is a classical semiconductor with a narrow bandgap, a high temperature coefficient of resistance, and phase transformation. Molybdenum ditelluride, a typical two-dimensional material, is often used to construct optoelectronic devices. The heterostructure can realize three different functional modes: (i) the p–n junction exhibits ultrasensitive detection (450 nm–2 μm) with a dark current down to 0.2 pA and a response time of 17 μs, (ii) the Schottky junction works stably under extreme conditions such as a high temperature of 400 K, and (iii) the bolometer shows ultrabroad spectrum detection exceeding 10 μm. The flexible switching between the three modes makes the heterostructure a potential candidate for next-generation photodetectors from visible to longwave infrared radiation (LWIR). This type of photodetector combines versatile detection modes, shedding light on the hybrid application of novel and traditional materials, and is a prototype of advanced optoelectronic devices.

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Nanoscale morphology of vanadium dioxide (VO 2 ) thin films can be controlled to realize smooth ultrathin crystalline films (<10 nm) with a simple way of DC sputtering. Here, crystallization annealing conditions determine whether a continuous ultrathin film or nanoparticle morphology is obtained. The experiments show that ultrathin VO 2 thin films possess both a highly crystal orientation (020) and an obvious metal-insulator transition (MIT). Meanwhile, optical transmittance between the visible and near-infrared regions can be modulated by thin film thickness, and the strain in the VO 2 lattice is also found to be dependent on the thin film thickness. The 8 nm thickness thin film shows that the change of resistance and visible transmittance is 2.8 orders of magnitude and 77.5%, respectively.

Vanadium dioxide (VO2), due to its electrically induced metal-to-insulator transition with dramatic changes in electrical and optical properties, is considered to be a powerful material for electro-optical devices. However, there are still some controversies about phase transition mechanism under voltage. Here, based on optical characterizations on VO2 crystal nanofilm during the whole process of phase transition, temporal evolution and spatial distribution of changes in electricity, optic and temperature are investigated simultaneously, to explore the mechanism. The variations of Raman spectrum and reflected spectrum, and changes in current and temperature are evidences for occurrence of phase transition, which exhibit different changing behaviors with time and space. These results offer a better understanding of the phase transition mechanism, implying that lattice structure of VO2 changes gradually after applying voltage until the structure is completely converted to metallic structure, which causes a rapid increase in carrier density, resulting in a rapid change in current, reflected spectrum and temperature. Temperature rise before phase transition and applied electric field alone are not enough for triggering metal-insulator transition, but these two factors can act synergistically on structural transformation to induce phase transition.

CuIn5S8 was prepared by gradient freeze techniques. Doping was done, and annealing was carried out under various sulfur atmosphere vapor pressures and vacuum. HgIn2S4 was prepared by chemical vapor phase transport and was annealed under various sulfur vapor pressures. Both materials showed increased photocurrent density with photoetching at short circuit, which was particularly dramatic for HgIn2S4 . Purely n‐type response was seen for HgIn2S4 samples as well as for CuIn5S8 , except where phosphorus plus sulfur dopants were used (both n‐ and p‐type responses). Quantum efficiencies of carrier collection were 10–15% at short circuit for CuIn5S8 (maximum of 77%) and ∼22% for HgIn2S4 (maximum of 83%) in a polysulfide couple. Considerable increase in the short‐circuit current density and open‐circuit photovoltage could be obtained for CuIn5S8 in a Ce4+/3+ couple, but this was offset by substantial photocorrosion. Power efficiencies up to ∼0.4% and ∼0.2% were obtained for CuIn5S8 and HgIn2S4 , respectively. Stability in a polysulfide couple was up to ∼97% for CuIn5S8 and >99% for HgIn2S4 .