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Characteristics of the Current-Controlled Phase Transition of VO_{2} Microwires for Hybrid Optoelectronic Devices

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## Abstract

**:**

_{2}) enable the realization of power-efficient, miniaturized hybrid optoelectronic devices. This work studies the current-controlled, two-step insulator-metal phase transition of VO

_{2}in varying microwire geometries. Geometry-dependent scaling trends extracted from current-voltage measurements show that the first step induced by carrier injection is delocalized over the microwire, while the second, thermally-induced step is localized to a filament about 1 to 2 μm wide for 100 nm-thick sputtered VO

_{2}films on SiO

_{2}. These effects are confirmed by direct infrared imaging, which also measures the change in optical absorption in the two steps. The difference between the threshold currents of the two steps increases as the microwires are narrowed. Micron- and sub-micron-wide VO

_{2}structures can be used to separate the two phase transition steps in photonic and electronic devices.

## 1. Introduction

**Figure 1.**(

**a**) The cross-section and (

**b**) top views of the wavelength-sized hybrid Si-VO${}_{2}$ electro-absorption switch and photodetector presented in [11]. (

**c**) A scanning electron micrograph of an etched VO${}_{2}$ strip atop a Si rib waveguide. This would form the active region of an electro-absorption switch/modulator.

**Figure 2.**(

**a**) The top and side view schematics of a VO${}_{2}$ lateral junction. (

**b**) A scanning electron micrograph of the device and (inset) the magnified image of the gap. (

**c**) The equivalent circuit model of the device in the experiment. (

**d**) The normalized resistivity of different microwires measured as the substrate temperature, T, for $W=5$ μm and $L=$ 750 nm, 10 μm and 50 μm.

## 2. Fabrication and Device Geometry

## 3. Current-Induced Phase Transition

**Figure 3.**The (

**a**) voltage-current and (

**b**) power-current relationship of a the VO${}_{2}$ wire with $L=5$ μm and $W=10$μm. The expected temperature of the VO${}_{2}$ is included in the right axis. (

**c**) The voltage-current and (

**d**) current-voltage relationship of a the VO${}_{2}$ wire with $L=1.25$ μm and $W=$ 2.5 μm, 10 μm and 50 μm.

#### 3.1. Critical Electric Fields

#### 3.2. Threshold Current Densities

**Figure 4.**(

**a**) The “average” electric field and (

**b**) the transition voltage offset for both transitions vs. W. The transition currents for the (

**c**) first and (

**d**) second transitions as a function of W for several values of L. The dissipated power density for the (

**e**) first and (

**f**) second transitions as a function L for several values of W.

## 4. Optical Absorption

**Figure 5.**The (

**a**) infrared and (

**b**) visible optical images of the VO${}_{2}$ device with $W=10$ μm and $L=5$ μm. (

**c**) The decrease in the infrared optical transmission as the current is increased. Each sub-figure corresponds to a current labelled in Figure 3a. (

**d**) The decrease in the infrared optical transmission after each transition and (

**e**) the width of the filament as a function of W when $L=5$ μm.

## 5. Discussion

## 6. Conclusions

## Acknowledgements

## Author Contributions

## Conflicts of Interest

## Appendix A: Experimental Details

#### A1. VO${}_{2}$ Sputtering

#### A2. Fabrication of the Etched VO${}_{2}$ Microwires

#### A3. Measurements

## Appendix B. VO${}_{2}$ Modelling and Simulations

#### B1. Thermal Modelling

#### B2. Electrical Modelling

**Figure B1.**The measured (symbols) and calculated (solid lines) resistance of VO${}_{2}$ wires as a function of L for several values wire W.

**Figure B2.**The (

**a**) measured and (

**b**) calculated change in the resistance of VO${}_{2}$ wires as a function of L and W.

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**MDPI and ACS Style**

Joushaghani, A.; Jeong, J.; Paradis, S.; Alain, D.; Aitchison, J.S.; Poon, J.K.S.
Characteristics of the Current-Controlled Phase Transition of VO_{2} Microwires for Hybrid Optoelectronic Devices. *Photonics* **2015**, *2*, 916-932.
https://doi.org/10.3390/photonics2030916

**AMA Style**

Joushaghani A, Jeong J, Paradis S, Alain D, Aitchison JS, Poon JKS.
Characteristics of the Current-Controlled Phase Transition of VO_{2} Microwires for Hybrid Optoelectronic Devices. *Photonics*. 2015; 2(3):916-932.
https://doi.org/10.3390/photonics2030916

**Chicago/Turabian Style**

Joushaghani, Arash, Junho Jeong, Suzanne Paradis, David Alain, J. Stewart Aitchison, and Joyce K.S. Poon.
2015. "Characteristics of the Current-Controlled Phase Transition of VO_{2} Microwires for Hybrid Optoelectronic Devices" *Photonics* 2, no. 3: 916-932.
https://doi.org/10.3390/photonics2030916