Multifield‐Inspired Tunable Carrier Effects Based on Ferroelectric‐Silicon PN Heterojunction

Abstract

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

Optically Controlled Ultrafast Terahertz Metadevices with Ultralow Pump Threshold

“…[ 46,49 ] Electrical control of THz modulation provides an effective strategy to realize the miniaturized setup and regional independence. [ 47,50,52,55,56,64 ] Inspired by our previous work, [ 47 ] current‐bias may support another feasible method to excite electro‐induced carriers aiding in switching off the Fano resonance. To validate this proposal, the pump fluence was firstly set 0, and we measured the THz transmission of the device under different current‐bias, shown in Figure a.…”

“…The terahertz (THz) waves residing in the frequency domain between infrared and microwave spectrum, [1][2][3] have earned considerable attention in the cutting edge of scientific fields meta-atoms always holds permanent optical properties, which is hard to be tuned actively. To achieve the dynamically control over THz waves across multiple dimensions of phase, frequency, and amplitude, continued progress has been devoted to this field by integrating metasurfaces with active materials, embracing traditional semiconductors, [44][45][46][47][48][49][50][51] liquid crystals, [52] phase change materials, [53,54] 2D materials (graphene and transition metal dichalcogenide), [55][56][57][58][59][60][61] and perovskites. [62,63] Besides, depending on the various properties of active materials, series of external stimulus including thermal, [53,54] optical, [44][45][46]48,49,51,57,58,62,63] voltage and current-biased met hods [47,50,52,55,56,64] have jointly promoted the development of THz metasurfaces in a more intelligent and multidimensional direction.…”

“…[58,62,63] For seeking miniaturized solution and spatial reconfiguration, electricalstimulus performs better than other methods to design active metasurfaces denoted as metadevices, due to the controllable selection property solely determined by the electrode configuration. [47,50,52,55,56,64] Nevertheless, most THz metadevices are usually responsive to single external driving field, being vulnerable if the single-stimulus equipment cannot operate well in some extreme conditions or if the power cannot meet the expected requirements.…”

“…To achieve the dynamically control over THz waves across multiple dimensions of phase, frequency, and amplitude, continued progress has been devoted to this field by integrating metasurfaces with active materials, embracing traditional semiconductors, [44][45][46][47][48][49][50][51] liquid crystals, [52] phase change materials, [53,54] 2D materials (graphene and transition metal dichalcogenide), [55][56][57][58][59][60][61] and perovskites. [62,63] Besides, depending on the various properties of active materials, series of external stimulus including thermal, [53,54] optical, [44][45][46]48,49,51,57,58,62,63] voltage and current-biased met hods [47,50,52,55,56,64] have jointly promoted the development of THz metasurfaces in a more intelligent and multidimensional direction. In terms of the modulation speed, optical pump has the unique advantage in achieving ultrafast switching at nanosecond or picosecond levels, owing to the merit of ultrashort relaxation time of photo-generated carriers.…”

Dual‐Sensitivity Terahertz Metasensor Based on Lattice–Toroidal‐Coupled Resonance

“…All measurements were carried out at room temperature and relatively dry condition with a humidity of 35% to eliminate the absorption of THz waves by water vapor. The transmission amplitude was obtained by , with and being the electric‐field amplitudes transmitted through the sample and reference substrate, [ 55 ] respectively.…”