Gate-field-induced phase transitions in VO2: Monoclinic metal phase separation and switchable infrared reflections

Abstract

In a metal-oxide-semiconductor VO2 active layer under uniaxial stress, gate-field-induced phase transitions are revealed by strongly field-dependent Raman scattering and infrared reflections. A metal-insulator transition (MIT) is demonstrated by a strongly correlated monoclinic metal phase separation that percolates, thereby making the reflections switchable. In addition, the MIT occurs at a gate voltage around 3.36V, much lower than the threshold of a structural phase transition (SPT). Hence, the MIT is easily controlled by the gate field to avoid the SPT-caused fatigue and breakdown in high-speed operation.

Optical properties for the Mott transition in VO2

“…17,20 In accordance with past results, the rutile tetragonal phase is observed near 70 • C after the MIT occurs. In our Raman measurements, although the rutile tetragonal phase indicating the SPT is not observed, a significant change of crystalline structure is shown above 75 • C. Thus, the SPT temperature may be regarded as 75 • C and it may be considered that a first-order MIT in VO 2 is not a structure-driven MIT.…”

“…At room temperature, seven peaks regarding as the phonon modes of the monoclinic phase for VO 2 are observed. [15][16][17] The modes observed at 192, 222, 259, 308, 338, 388, and 498 cm -1 are confirmed as A g symmetry of the phonons. 16,17 The peaks at 142 and 613 cm -1 are also assigned to the B 1g and A 1g symmetric modes, respectively.…”

“…[15][16][17] The modes observed at 192, 222, 259, 308, 338, 388, and 498 cm -1 are confirmed as A g symmetry of the phonons. 16,17 The peaks at 142 and 613 cm -1 are also assigned to the B 1g and A 1g symmetric modes, respectively. 17 In the temperature range from room temperature to 72 • C, all peaks of the typical Raman-active modes for the monoclinic phase significantly weaken and broaden.…”

“…16,17 The peaks at 142 and 613 cm -1 are also assigned to the B 1g and A 1g symmetric modes, respectively. 17 In the temperature range from room temperature to 72 • C, all peaks of the typical Raman-active modes for the monoclinic phase significantly weaken and broaden. The peaks disappear at 75 • C. In our measurements, although the tetragonal A 1g peak indicating the SPT from the monoclinic to the rutile tetragonal structure 17,18 is not observed, the disappearance of the typical Raman-active modes for the monoclinic phase above 75 • C points out a variation of crystalline structure in VO 2 .…”

Transport behavior and electronic structure of phase pure VO2 thin films grown on c-plane sapphire under different O2 partial pressure

“…Thanks to the improvements in the quality of VO 2 thin films, there has been a growing emphasis on exploring logic and memory device applications of this intriguing phenomenon. Recent efforts on a Mott field effect transistor (MottFET) have demonstrated that VO 2 can be employed as the channel in a MottFET, and the applied external gate voltage switches the channel resistance between the insulating OFF state and the metallic ON state [4][5][6] . There are still several challenges for these so called "Mott devices" 7 , among which is a concern over the repeatability/reproducibility of the Mott transition because the properties of these materials are sensitive to oxygen vacancy concentration, strain, and other factors.…”