Determination of the correlation between aluminum, tungsten doping and Hall Effect parameters on the optical properties of vo2 based thin films
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Date
2016
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Publisher
University of Dar es Salaam
Abstract
This study focused on the determination of the correlation between Al, W doping and Hall Effect parameters with a view to explain changes in the optical properties of V02 thin films. The films were prepared on soda lime glass slides by dc reactive magnetron sputtering of vanadium target, vanadium doped tungsten alloy target (V990/0 - W 1%) and vanadium doped tungsten alloy target stuck with aluminum pellets (V : W: Al) in a mixture of argon and oxygen gases. The working pressure was 5.6 —- 6.2 x 10-3 mbar and the substrate temperature was 450 oc. The argon flow rate was 75 mln/ min while oxygen flow rate was varied from 6.6 to 7.2mln/ min. Sheet resistance of the films was obtained using a two-point probe. The Hall Effect parameters of the films were investigated by using Ecopia HMS-3000 Hall Effect measurement system. A Perkin Elmer UV/VIS/NIR Lambda 9 spectrophotometer was used to measure the optical properties of the films in the wavelengths range of 300 — 2200 nm. The phase transition temperatures were obtained from both the transmittance -vs-temperature and sheet resistance - vs - temperature curves. A change in sheet resistance of 3 orders of magnitude across the phase transition temperature was recorded for all films. The carrier concentration and conductivity of all films increases with increase in temperature while carrier mobility was observed to decrease with increase in temperature. A change of 3 and 2 orders of magnitude for carrier concentration and conductivity across the transition temperature was recorded for both undoped, W doped and Al, W co-doped V02 thin films. Tungsten doped films had higher carrier concentration and conductivity on both sides of the MIT and low mobility compared to undoped and co-doped V02 thin films. The results further revealed that V02: W: Al thin films improved the luminous transmittance to about 58 % and reduced the transition temperature to 54 ℃ compared to 41 % and 68 ℃ respectively, for undoped V02 thin film. The W doped V02 films had a lower transition temperature of 33 ℃ but the luminous transmittance was as low as 36%. Optical properties for V02, V02: W and V02: W: Al thin films showed strong dependency on the Hall Effect parameters.
Description
Available in print form, Eat Africana Collection, Dr. Wilbert Chagula Library,(THS EAF QC176.84.O7M87)
Keywords
Thin films, Optical properties
Citation
Mussa, M. (2016) Determination of the correlation between aluminum, tungsten doping and Hall Effect parameters on the optical properties of vo2 based thin films. Masters dissertation, University of Dar es Salaam, Dar es Salaam.