Date of Award

1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

First Advisor

Pratul K. Ajmera

Abstract

Photochemical means have been utilized to deposit arsenic, gallium and gallium arsenide thin films in an attempt to achieve deposition of gallium arsenide at substrate temperatures lower than those utilized in conventional organometallic chemical vapor deposition. Photolysis, Hg-photosensitization and light-driven pyrolysis have been utilized to obtain thin films on quartz, fused silica, gallium arsenide and silicon substrates. Triethylgallium and arsine served as the reactants with a low pressure Hg lamp, a high pressure Hg-Xe arc lamp and an ArF excimer laser serving as the ultraviolet radiation sources. Deposition of arsenic and gallium arsenide thin films on quartz was investigated utilizing Hg-photosensitization. Arsenic thin films were deposited on quartz by means of Hg-sensitized decomposition of arsine at substrate temperatures ranging from 50 to 240$\sp\circ$C. Films deposited below 200$\sp\circ$C were found to be amorphous while those deposited above 200$\sp\circ$C consisted of rhombohedral arsenic. Gallium arsenide deposition at temperatures less than 250$\sp\circ$C utilizing Hg-photosensitization occurred only in the presence of an additional broadband ultraviolet light source. Polycrystalline gallium arsenide thin films were obtained on quartz substrates using both a low pressure Hg lamp and a Hg-Xe arc lamp. Direct photochemical vapor deposition of gallium arsenide was also achieved on fused silica, gallium arsenide and silicon substrates. The film stoichiometry was highly dependent on the substrate temperature with arsenic-rich films obtained for substrate temperatures below approximately 250$\sp\circ$C. Single crystal gallium arsenide thin films were obtained on gallium arsenide substrates at a substrate temperature of approximately 315$\sp\circ$C with room temperature Hall mobility values as high as 4000 cm$\sp2$/V-sec. It was found that, for perpendicular beam geometry, both photolytic and pyrolytic mechanisms contributed to the thin film growth. A mass spectroscopic study of the photolytic decomposition of the two reactants was also performed. In addition, a simple first-order model is presented for light-driven chemical vapor deposition of gallium arsenide at low substrate temperatures for which both gas-phase and surface-adsorbed species photodissociate. Results of this work indicate that the photodissociation of surface-adsorbed species is the more useful process for achieving stoichiometric GaAs deposition at low temperatures using photochemical means.

Pages

189

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