Date of Award

Summer 2003

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering - (M.S.)

Department

Electrical and Computer Engineering

First Advisor

Leonid Tsybeskov

Second Advisor

Durgamadhab Misra

Third Advisor

Marek Sosnowski

Abstract

The dc current-voltage characteristics, ac conductivity, equivalent capacitance, photocurrent transients of the n-Si/nanocrystalline-Si/amorphous-SiO2/Al heterostructure were measured in a wide range of illumination intensities for temperatures from 4.2 K to 300 K. Electrical transport properties of the nanocrystalline-Si/amorphous-SiO2 superlattices were discussed. The observed domination of the electron component at negative bias and of the hole component at positive bias above 0.7 V in a dc current allows to separate transport features of electrons and holes in a nc-Si/a-SiO2 superlattices. Transport of electrons is thermally activated if potential barrier at c-Si/SL interface of 70 meV is suppressed and several activation energies for different temperature regions were determined. Transport of holes is well described by the Fowler-Nordheim tunneling theory for a number of illumination intensities in the measured temperature region. Tunneling mechanism is additionally supported by an independence of the photocurrent decay on temperature. Two maxima in ac conductivity at 0 V and at 0.8 V were related to trap-assisted conductivity and to alignment of energy levels in the heterostructure (photoconductivity resonance), respectively. Time-dependent photocurrent measurements proved a decrease of the photoconductivity due to a decreasing mobility of holes and misalignment of the energy levels at bias above O.8V. Density of traps of 3.5x1011cm-2 and trapping time of 30 μs were found. An application of nanocrystalline Si/amporphous SiO2 superlattices in non-volatile memory devices is discussed.

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