the entire modulation process. Due to their unique electronic and optical characteristics, 2D and quasi-2D materials are emerging as exciting material systems for a new generation of layered optoelectronics, [11,12] such as photodetectors, [13,14] polarizers, [15] solar cells, [3,[16][17][18] and optical modulators. [19,20] For instance, graphene has many intriguing mechanical, electronic, thermal, and optical properties because the electrons behave as massless Dirac fermions and exhibit the highest mobility. [21,22] 2D transition-metal dichalcogenides (TMDs) change from indirect semiconductors to direct semiconductors when thinned to monolayers, showing remarkable optoelectronic properties. [23] The formation mechanism of traditional carrier layers is usually based on the high carrier mobility of 2D and quasi-2D materials. Although significant progress has been achieved through years of research, the preparation technology of new 2D materials, such as graphene and monolayer TMDs, is not mature and stable. To meet the demand for large-scale preparation of 2D materials with stable performance, improving the preparation technology, exploring new design mechanisms, or seeking other stable materials as candidates is urgent.Ferroelectrics are such stable materials with simple preparation methods. Additionally, the domains can be controlled via electric, thermal, optical, and mechanical fields, [24][25][26][27][28] meaning that the bound surface charges of ferroelectrics can be modulated under single-field or multifield coupling. Inspired by the PN heterojunction effect, in which the generation of current carriers in the space charge region can be extremely high, [29][30][31][32][33][34][35] combining ferroelectrics and semiconductors with high carrier mobility to construct PN heterojunctions may be an effective way to form a carrier layer and achieve carrier modulation.To demonstrate this concept, N-type silicon with a bandgap of 1.12 eV is chosen as the semiconductor material, which can guarantee sufficient free electrons under optical field. Ferroelectrics usually have a Curie temperature T 0 above which they are in a paraelectric phase state. Due to its good dielectric performance with significant dielectric nonlinearity over a wide temperature range near T 0 , Ba 0.7 Sr 0.3 TiO 3 (BST) thin film is chosen as the ferroelectric material. By depositing the BST thin film directly onto a silicon substrate, the BST-silicon PN heterojunction is constructed, deriving from the interaction between

With the drafting of the 6G white paper, terahertz (THz) modulators reshow profound significance in wireless communication, data storage, and imaging. Active tuning of THz waves through hybrid meta-structure incorporated with smart materials has attracted keen interest due to the deliberate structural design and dynamic transition of material properties. However, until now, these meta-devices have usually been responsive to a single driving field, such as electrical, thermal, or optical stimuli, which hinders their applicability for multidimensional manipulation of THz waves. Herein, to the best of our knowledge, a Ba0.6Sr0.4TiO3–silicon hybrid meta-modulator to achieve opposite tuning of the amplitude characteristic with two different types of stimuli is proposed for the first time. When driven by an external voltage, the proposed meta-modulator exhibits enhanced transmittance. In contrast, the transmission coefficient gradually decays as the external current increases. This outstanding performance is systematically studied by analyzing the carrier transport in the meta-structure as well as the change in the dielectric constant. Our research provides a novel idea for the development of actively tunable THz meta-devices and paves the way for robust multifunctionality in electrically controlled THz switching, and biosensors.

In this paper we propose a design method for a thermally tunable frequencyselective surface (FSS) in the THz frequency range employing barium strontium titanate (BST) thin film. Due to the excellent thermoelectric properties of BST, different relative permittivities can be obtained at different temperatures. With this ability, the passband frequency of the FSS can be tuned by changing the temperature of the BST thin film. The metallic element array of the FSS is designed using the metamaterial method. A convenient method for thermal control is proposed that uses microfabricated electric heating wires; these can provide different temperatures by altering the input electric current. Full wave simulations show good performance of thermally tunable frequency selective transmission at THz frequencies. The proposed FSS is then fabricated and measured. The experimental results agree well with the simulation. By changing the temperature of the BST thin film, the passband can be tuned from 0.826 THz to 0.905 THz. This work proposes a THz tunable FSS based on BST thin film, which promotes connections between ferroelectric films and tunable THz functional devices.

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Vanadium oxide (VO2), as one of the classical strongly correlated oxides with a reversible and sharp insulator-metal transition (IMT), enables many applications in dynamic terahertz (THz) wave control. Recently, due to the inherent phase transition hysteresis feature, VO2 has shown favorable application prospects in memory-related devices once combined with metamaterials or metasurfaces. However, to date, VO2-based memory meta-devices are usually in a single-channel read/write mode, which limits their storage capacity and speed. In this paper, we propose a reconfigurable meta-memory based on VO2, which favors a two-channel read/write mode. Our design consists of a pair of large and small split-ring resonators, and the corresponding VO2 patterns are embedded in the gap locations. By controlling the external power supply, the two operation bands can be controlled independently to achieve at least four amplitude states, including “00”, “01”, “10”, and “11”, which results in a two-channel storage function. In addition, our research may provide prospective applications in fields such as THz switching, photon storage, and THz communication systems in the future.