Reactions of monomethylgallium, dimethylgallium, and trimethylgallium on silicon(100) and indium phosphide(100)
Lin, Robert
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Permalink
https://hdl.handle.net/2142/20168
Description
Title
Reactions of monomethylgallium, dimethylgallium, and trimethylgallium on silicon(100) and indium phosphide(100)
Author(s)
Lin, Robert
Issue Date
1992
Doctoral Committee Chair(s)
Masel, Richard I.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
Trimethylgallium (TMGa) is a common source gas in GaAs film production by MOCVD, MOMBE, and ALE. The first of three sections explores the low pressure gas phase production of dimethylgallium (DMGa) and monomethylgallium (MMGa) in a heated metal tube reactor. Quantitative measurements of Ga-alkyls species were obtained by a mass spectrometer in ultrahigh vacuum. TMGa pyrolyzes by breaking a Ga-C bond forming DMGa at 300 K. Two more Ga-C bonds are cleaved producing MMGa and Ga at 710 and 800 K respectively. The primary hydrocarbon products are methyl radicals and methane. Apparent activation energy for TMGa decomposition was measured at 4.7 kcal/mol.
The second section explores reactions of TMGa multilayert on Si(100) using TPD and XPS. At TMGa exposures ${>1}\times 10\sp{16}$ molecules/cm$\sp2$, TMGa transiently populates a weakly bound state which desorbs if the sample is held in vacuum for several minutes at 300 K. However, the multilayer TMGa will react if the sample is flashed immediately after dosing. The weakly bound TMGa decomposes at 400-600 K to yield DMGa$\sb{\rm (abs)}$, methane, and CH$\sb{\rm x}$ groups. The DMGa reacts upon further heating to yield MMGa$\sb{\rm (abs)}$, methane and additional CH$\sb{\rm x}$ groups. The MMGa decomposes above 700 K to yield methyl radicals and gallium. Traces of ethylene are also seen. These results verify that carbon deposition is an intrinsic part of TMGa decomposition on Si(100). In contrast, MMGa can decompose cleanly. Hence, MMGa may be a promising intermediate for MOMBE.
The third section explores the reactions of TMGa, DMGa, and MMGa on single crystal InP(100). Results of TPD and XPS experiments show that TMGa is relatively unreactive on InP(100) compared to DMGa and MMGa. Adsorbed DMGa disproportionates to TMGa and MMGa. Adsorbed MMGa disproportionates to DMGa and elemental Ga. Therefore, DMGa and MMGa are useful Ga sources even though TMGa is unreactive. Additionally, there is some evidence of elemental gallium displacing indium in the InP lattice forming GaP. This work is the first to examine the decomposition of metalorganics on single crystal InP using thermal desorption techniques.
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