Growth and Optoelectronic Properties of Diamond Films Prepared by Chemical Vapor Deposition.
The formation of diamond under metastable conditions (low pressure and temperature) is one of the most interesting problems in the science of crystal growth, since under such conditions graphite is expected to be the thermodynamically stable phase of carbon. In this dissertation, a number of issues related to the nucleation and growth as well as optoelectronic properties of diamond films are addressed. The films were deposited by decomposition of mixtures of hydrogen and carbon-containing molecules using various forms of microwave plasmas. The role of the nature, treatment, and electrical biasing of the substrates, as well as the role of impurities, such as oxygen and nitrogen on the growth and properties of the films were investigated. Growth at very low pressures using electron cyclotron resonance assisted plasmas leads to films with significantly different microstructure and kinetics of growth than films produced by alternative methods. As the temperature increases from 425^circC to 1050 ^circC, the dominant surface morphology changes from octahedral (111), to cubic (100), and then to multiple twinned (111) crystals. An Arrhenius plot of the growth rate as s function of temperature gives rise to an activation energy of 4 kcal/mol, much less than 20 -30 kcal/mol reported in other growth methods. The observed value is consistent with the notion that hydrogen removal from the growing surface controls the rate of film growth. The role of nitrogen impurities in the evolution of film morphology was investigated. It was found that when the ratio of N/C in the gas phase is 10% or larger, the surface morphology converts from (111) to (100). This result was attributed to the unique large distortion along the (111) directions of the C-N bond which prohibits epitaxy along this direction. The incorporation of impurities, such as boron and nitrogen, was also investigated by studying the electrical conductivity along the growth direction. A strong correlation was found between film morphology and electrical conductivity activation energy, and attributed to the preferential activation of boron and nitrogen when growth proceeds along the (111) and (100) directions respectively. Finally, the electronic properties of undoped diamond films were investigated by conductivity, photoluminescence, and electron paramagnetic resonance studies, and a model regarding the electronic defect structure of such films is proposed.
- Pub Date:
- January 1994
- Physics: Condensed Matter