Optimizing the Charge Carrier Dynamics of Thermal Evaporated TexSe1-x Films for High-Performance Short-Wavelength Infrared Photodetection

Short-wavelength infrared photo-sensing materials are dominated by germanium, indium gallium arsenide, indium antimonide, and mercury cadmium telluride. However, the complex fabrication process and high production cost hinder their widespread applications. Recently, Te_xSe_1-x has shown great potential for infrared photodetection, but Te_xSe_1-x-based devices are still suffering from extremely high dark current and poor device performance. In this work, high-quality Te_xSe_1-x films are fabricated by thermal evaporation and low-temperature annealing. The optoelectronic properties of the Te_xSe_1-x thin films are systematically investigated and optimized. The absorption spectrum is carefully tuned to cover the broad range from 300 to 1600 nm by modulating the ratio of Te and Se. Photodiodes based on the optimized Te_xSe_1-x thin films are also fabricated, and achieve high responsivity, reduced dark and low noise current density, and a fast response time of <850 ns. Then, prototypical devices based on Te_0.65Se_0.35 thin films are demonstrated for optical communications, indicating the great potential for next-generation, low-cost short-wavelength infrared photodetection.     

3D Bicontinuous Nanoporous Reduced Graphene Oxide for Highly Sensitive Photodetectors

Reduced graphene oxide (RGO) is an important graphene derivative for applications in photonics and optoelectronics because of the band gap created by chemical oxidation. However, most RGO materials made by chemically exfoliated graphite oxide are 2D flakes. Their optoelectronic performance deteriorates significantly as a result of weak light‐matter interaction and poor electrical contact between stacking flakes. Here we report a bicontinuous 3D nanoporous RGO (3D np‐RGO) with high optoelectronic performance for highly sensitive photodetectors. 3D np‐RGO demonstrates a over 40 times higher light absorption than monolayer graphene materials and at least two orders of magnitude higher electron mobility than conventional RGO from discrete RGO flakes. The np‐RGO with an optimal reduction state shows ultrahigh photoresponse of 3.10 3 10⁴ A W^?1 at room temperature, approximately four orders of magnitude higher than graphene and other graphene derivatives at similar levels of light intensity radiations, and the excellent external quantum efficiency of 1.04 3 10⁷% better than commercial silicon photodetector. The ultrahigh capability of conversing photons to photocurrent originates from strongly enhanced light absorption, facilitated photocarrier transport, and tunable oxygenous defects and reduction states in the 3D interconnected bicontinuous RGO network.     

Highly In-Plane Anisotropic 2D PdSe2 for Polarized Photodetection with Orientation Selectivity

Polarized photodetection based on anisotropic two-dimensional materials display promising prospects for practical application in optical communication and optoelectronic fields. However, most of the reported polarized photodetection are limited by the lack of valid tunable strategy and low linear dichroism ratio. A peculiar noble metal dichalcogenide—PdSe₂ with a puckered pentagonal structure and abnormal linear dichroism conversion—potentially removes these restrictions and is demonstrated in this study. Herein, azimuth-dependent reflectance difference microscopy combined with anisotropic electrical transport measurements indicate strong in-plane anisotropic optical and electrical properties of two-dimensional PdSe₂. Remarkably, the typical polarization-resolved photodetection exhibits anisotropic photodetection characteristics with a dichroic ratio up to ≈1.8 at 532 nm and ≈2.2 at 369 nm, and their dominant polarization orientation differs by 90° corresponding to the a-axis and b-axis, respectively. The unique orientation selection behavior in polarization-dependent photodetection can be attributed to the intrinsic linear dichroism conversion. The results make 2D PdSe₂ a promising platform for investigating anisotropic structure–property correlations and integrated optical applications for novel polarization-sensitive photodetection.     

Growth of Highly Anisotropic 2D Ternary CaTe2O5 Flakes on Molten Glass

Two‐dimensional (2D) ternary compounds (2DTCs) have attracted intensive attention due to the new degree of freedom of modulating physical and chemical properties. However, the controllable synthesis of 2DTCs still remains a great challenge impeding further research and applications. Here, for the first time, ultrathin (≈7.4 nm) ε‐CaTe₂O₅ flakes with high anisotropy are obtained by a chemical vapor deposition method using soda‐lime glass as the capture substrate. The molten glass adsorbs Te vapor in the gas flow to its surface, which reacts with CaO in the molten substrate leading to the precipitation of ε‐CaTe₂O₅. Interestingly, ε‐CaTe₂O₅ flakes display highly anisotropic band structures and optical properties. Furthermore, low‐temperature electrical measurements show that the metal–semiconductor/insulator transition of ε‐CaTe₂O₅ is exhibited at about 130 K, and optical phonon assisted hopping of small polarons becomes dominant within the temperature range of 130–300 K. Employing soda‐lime glass as the capture substrate may provide a new approach for the synthesis of 2DTCs.     

Simultaneous Edge‐on to Face‐on Reorientation and 1D Alignment of Small π‐Conjugated Molecules Using Room‐Temperature Mechanical Rubbing

In this study, room‐temperature mechanical rubbing is used to control the 3D orientation of small π‐conjugated molecular systems in solution‐processed polycrystalline thin films without using any alignment substrate. High absorption dichroic ratio and significant anisotropy in charge carrier mobilities (up to 130) measured in transistor configuration are obtained in rubbed organic films based on the ambipolar quinoidal quaterthiophene (QQT(CN)4). Moreover, a solvent vapor annealing treatment of the rubbed film is found to improve the optical and charge transport anisotropy due to an increased crystallinity. X‐ray diffraction and atomic force microscopy measurements demonstrate that rubbing does not only lead to an excellent 1D orientation of the QQT(CN)4 molecules over large areas but also modifies the orientation of the crystals, moving molecules from an edge‐on to a face‐on configuration. The reasons why a mechanical alignment technique can be used at room temperature for such a polycrystalline film are rationalized, by the plastic characteristics of the QQT(CN)4 layer and the role of the flexible alkyl side chains in the molecular packing. This nearly complete conversion from edge‐on to face‐on orientation by mechanical treatment in polycrystalline small‐molecule‐based thin films opens perspectives in terms of fundamental research and practical applications in organic optoelectronics.