Multifield-Modulated Spintronic Terahertz Emitter Based on a Vanadium Dioxide Phase Transition

The efficient generation and active modulation of terahertz (THz) waves are strongly required for the development of various THz applications such as THz imaging/spectroscopy and THz communication. In addition, due to the increasing degree of integration for the THz optoelectronic devices, miniaturizing the complex THz system into a compact unit is also important and necessary. Today, integrating the THz source with the modulator to develop a powerful, easy-to-adjust, and scalable or on-chip THz emitter is still a challenge. As a new type of THz emitter, a spintronic THz emitter has attracted a great deal of attention due to its advantages of high efficiency, ultrawide band, low cost, and easy integration. In this study, we have proposed a multifield-modulated spintronic THz emitter based on the VO2/Ni/Pt multilayer film structure with a wide band region of 0–3 THz. Because of the pronounced phase transition of the integrated VO2 layer, the fabricated THz emitter can be efficiently modulated via thermal or electric stimuli with a modulation depth of about one order of magnitude; the modulation depths under thermal stimulation and electrical stimulation were 91.8% and 97.3%, respectively. It is believed that this multifield modulated spintronic THz emitter will provide various possibilities for the integration of next-generation on-chip THz sources and THz modulators

Hole Carriers Doping Effect on the Metal–Insulator Transition of N‑Incorporated Vanadium Dioxide Thin Films

The coupling of doped charge carriers with the crystal lattice is an efficient route to modulate the phase transition behavior of VO₂. In the current work, the N-incorporated VO₂ samples are prepared through the low-energy N₂⁺ ion sputtering of the crystalline VO₂ films. The critical temperatures (<i>T</i>_c) of the metal–insulator transition (MIT) process are observed to decrease with a value of ∼18 °C for VO_1.9N_0.1 and VO_1.87N_0.13 samples. The effects of nitrogen incorporation on the MIT depression have been revealed by the electronic structural characterizations via the X-ray adsorption near-edge structure (XANES) spectroscopy and photon electronic spectroscopy (SRPES). The implanted nitrogen atoms are identified to coordinate with the V⁴⁺ ions at the substituent position of oxygen atoms. The p-type dopant provides the hole carriers into the d_∥ sub-bands, resulting in the attenuation of the interaction within V–V dimer and the narrowing of the energy band gap in M1 phase. Both aspects unanimously facilitate the depression of the MIT temperature in N-incorporated VO₂