Browsing by Author "Stokes, Scott Wilson"
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Item Laser-assisted metalorganic chemical vapor deposition of zinc sulfide(1997) Stokes, Scott Wilson; Wilson, William L., Jr.Laser-assisted metalorganic chemical vapor deposition (MOCVD) was used to grow crystalline zinc sulfide at temperatures as low as 200$\sp\circ$C. The metalorganic sources, dimethylzinc and diethylsulfide, were photodissociated with radiation from a 193 nm ArF excimer laser passing parallel to the substrate. Epitaxial films were grown on gallium arsenide by both the thermal and laser-assisted MOCVD methods. Zinc sulfide films grown on silicon substrates were polycrystalline possibly due to a reaction between sulfur and the silicon substrate creating an amorphous compound at the interface. X-ray diffraction and photoluminescence results indicate that films grown by laser-assisted MOCVD below 500$\sp\circ$C on either substrate were not as high quality as those grown above 500$\sp\circ$C. It is postulated that increased hydrocarbon contamination in the low temperature laser-assisted MOCVD grown films is responsible for the decrease in film quality.Item Low-frequency noise in spin valve sensors(1999) Stokes, Scott Wilson; Wilson, William L., Jr.Low frequency noise in giant magnetoresistive spin valves has been studied as a means of optimizing signal to noise ratios and characterizing device performance. The devices studied were sputter deposited NiFe/Cu/NiFe/FeMn spin valves with D R/R ∼ 4%. Static measurements demonstrated a strong dependence of the magnetic coupling and giant magnetoresistance (GMR) ratio on the thickness and quality of the Cu spacer layer and the bottom NiFe layer (free layer). These parameters were varied to determine how the noise in spin valve sensors would be affected. Noise power spectra were measured in patterned spin valves. The noise was observed to have a 1/f slope at low frequencies. The fluctuation-dissipation relation relating thermal fluctuations in magnetization to the resistance fluctuations was used to explain the origin of the 1/f noise. The noise was found to be sensitive to the anisotropy and defect density of the free layer. The noise was minimized for spin valves operating with parallel anisotropy axes and an applied field aligned along the hard axis of magnetization. Dynamic fields were used to measure the Barkhausen noise in the sense layer of the spin valve. The low frequency noise in the presence of dynamic fields was much greater than the 1/f noise background. Clustering of Barkhausen jumps was used to explain the observed dependence of the noise power on the magnitude and frequency of the applied field. Higher frequency signals resulted in lower Barkhausen noise. The noise was reduced when the applied field was aligned along the hard axis of magnetization.