Abstract
The parameters of reactive pulsed laser deposition were successfully optimized for fabrication of vanadium dioxide thin films. It is observed that the
O
2
concentration in Ar gas and the total deposition pressure are critical in stabilizing the single
VO
2
phase. Thermochromic
VO
2
and
V
1−x
W
x
O
2
(x=0.014)
thin films were synthesized on various substrates (silicon, quartz, and sapphire) at 5% of
O
2
/
Ar
ratio gas and total pressure of 90 mTorr. The structural properties of the deposited films were analyzed by x-ray diffraction, while their semiconductor-to-metal phase transitions were studied by electrical resistivity using the four-point technique and infrared transmittance from room temperature up to 100 °C. The observed transition temperature was about 36 °C for W-doped
VO
2
compared to 68 °C for
VO
2
films. This transition temperature was then lowered by about 22.85 °C per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/°C for
VO
2
and about 1.90%/°C for W-doped
VO
2
.
Using the pump-probe experiment, the application of these thermochromic films as optical switches was demonstrated at the wavelength of 1.55 μm. The transmission switching was about 25 dB for
VO
2
and 28 dB for W-doped
VO
2
.
In addition, application of
VO
2
on optical fiber components was demonstrated by direct
VO
2
coating on the end faces of cleaved single mode optical fibers and optical fiber connectors.