Graduation Year

2006

Document Type

Thesis

Degree

M.A.

Degree Granting Department

Physics

Major Professor

Sarath Witanachchi, Ph.D.

Committee Member

Dale Johnson, Ph.D.

Committee Member

Myung K. Kim, Ph.D.

Keywords

pulse laser deposition, hall voltage measurements, iron probe, iv characteristics

Abstract

Iron Silicide (FeSi) films deposited on silicon substrates with the native SiO2 layer have shown a Metal-to-Insulator Transition (MIT) of more than four order of magnitude change in resistance. Modification of the SiO2/Si interface due to Fe diffusion has been attributed to the formation of this effect. In this research a systematic experimental investigation has been carried out to study the effect of the growth parameters and substrate doping type in the transition. In addition, transport properties of continuous and discontinuous films have been investigated to understand the mechanism of this metal-to-insulator transition.

Four probe measurements of films deposited in p- and n-type doped Si substrates with resistivity in the range of 1-10 Ωcm showed similar temperature dependent resistance behavior with transition onsets at 250 K and 300 K respectively. These results indicate that the current transport takes place via tunneling through the SiO2 layer into the Si substrate up to the transition temperature. Current appears to switch to the film after the transition point due to the development of high interface resistance. Discontinuous FeSi films on silicon substrates showed similar resistance behavior ruling out possibility of current transport through inversion layer at the SiO2/Si interface.

To investigate the role of the magnetic ion Fe, transport measurements of FeSi films were compared with those of non-magnetic metals such as Platinum (Pt) and Aluminum (Al). Absence of Metal-to-insulator transition on Pt and Al films show that the presence of magnetic moment is required for this transition.

Temperature dependent Hall voltage measurements were carried out to identify the carrier type through the substrate for FeSi films deposited on p- and n-type Si substrates. Results of Hall voltage measurements proved that the type of conductivity flips from majority carriers to minority after the transition.

Metal-to-insulating transition behavior of FeSi films depending on different laser fluences has been also investigated. Our results revealed as laser fluence is increased observed transition of the FeSi films reduces rapidly showing a highest magnitude of transition of about 1 MΩ for the films deposited with lowest laser fluence (0.64 J/cm2 ) and a lowest of about 10 Ω for the films deposited with highest laser fluence (3.83 J/cm2 ). Ion probe measurements indicated that the average kinetic energy of the ablated ion in the plume is considerably increased with the increase of the laser fluence. Consequently, magnitude drop in the transition can be considered due to the deeper penetration on Fe ion through the SiO2 layer.

Thickness dependence study carried out for FeSi films deposited with high and low laser fluencies indicated transition slightly drops as thickness is increased, concluding the current transportation through the film becomes dominant after the transition temperature.

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