Optical switching of vanadium dioxide thin films deposited by reactive pulsed laser deposition

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 VO2 phase. Thermochromic VO2 and V1-xWxO2(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 degreesC. The observed transition temperature was about 36 degreesC for W-doped VO2 compared to 68 degreesC for VO2 films. This transition temperature was then lowered by about 22.85 degreesC per 1 at. % of W added. The temperature coefficient of resistance was about 1.78%/degreesC for VO2 and about 1.90%/degreesC for W-doped VO2. Using the pump-probe experiment, the application of these thermochromic films as optical switches was demonstrated at the wavelength of 1.55 mum. The transmission switching was about 25 dB for VO2 and 28 dB for W-doped VO2 - In addition, application of VO2 on optical fiber components was demonstrated by direct VO2 coating on the end faces of cleaved single mode optical fibers and optical fiber connectors. (C) 2004 American Vacuum Society.