Degree Type

Dissertation

Date of Award

1991

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

Major

Solid State Physics

First Advisor

Howard R. Shanks

Second Advisor

Bruce N. Harmon

Abstract

Undoped and boron doped diamond thin films have been successfully grown by microwave plasma chemical vapor deposition from CH[subscript]4, H[subscript]2, and B[subscript]2H[subscript]6. The films were characterized using x-ray diffraction techniques, Raman and infrared spectroscopies, scanning electron microscopy, secondary ion mass spectrometry, and various electrical measurements. The deposition rates of the diamond films were found to increase with the CH[subscript]4 concentration, substrate temperature, and/or pressure, and at 1.0% methane, 900°C, and 35 Torr, the value was measured to be 0.87 [mu]m/hour. The deposition rate for boron doped diamond films, however, decreases as the diborane concentration increases. The morphologies of the undoped diamond films are strongly related to the deposition parameters. As the temperature increases from 840 to 925°C, the film morphology changes from cubo-octahedron to cubic structures, while as the CH[subscript]4 concentration increases from 0.5 to 1.0%, the morphology changes from triangular (111) faces with a weak preferred orientation to square (100) faces. Furthermore, at 2.0% CH[subscript]4 or higher the films become microcrystalline with cauliflower structures. Scanning electron microscopy analyses also demonstrate that selective deposition of undoped diamond films has been successfully achieved using a lift-off process with a resolution of at least 2 [mu]m. The x-ray diffraction and Raman spectra demonstrate that high quality diamond films have been achieved. The concentration of the nondiamond phases in the films grown at 1.0% CH[subscript]4 can be estimated from the Raman spectra to be less than 0.2% and increases with the CH[subscript]4 concentration. The Raman spectra of the boron doped diamond films also indicate that the presence of boron tends to suppress the nondiamond phases in the films. Infrared spectra of the undoped diamond films show very weak CH stretch peaks which suggest that the hydrogen concentration is very low. Infrared measurements on the boron doped diamond films provide a rapid way to detect the presence of boron in the films with a lower limit of less than 5.2 x 10[superscript]19 cm[superscript]-3. Secondary ion mass spectrometry analyses and various electrical measurements demonstrate that p type semiconducting diamond films have been successfully deposited. The boron concentration in the films depends strongly upon the boron concentration in the gas phase. The resistivity of the films and its activation energy were found to decrease as the boron concentration in the films increases. As the doping level increases from 3.0 x 10[superscript]19 to 42.0 x 10[superscript]19 cm[superscript]-3, the resistivity decreases from 43.57 to 0.08 [omega] cm. The activation energy of the films was measured to be from 0.013 to 0.158 eV depending upon the doping level. Blue-green electroluminescence has been observed from the undoped diamond films deposited using a step etching progress. The mechanism can be explained by donor-acceptor pair recombination. The donor and the acceptor are believed to be N and B, respectively. ftn*DOE Report IS-T-1558. This work was performed under contract No. W-7405-eng-82 with the U.S. Department of Energy.

DOI

https://doi.org/10.31274/rtd-180813-10874

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Moeljanto W. Leksono

Language

en

Proquest ID

AAI9212159

File Format

application/pdf

File Size

139 pages

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