Chemical vapor deposition and physical characterization of gallium, and carbon-related structures on Si (001) and GaP/Si (001) templates for the growth of graphene layers

This study aimed at the deposition of graphene on Si(001) via CVD by depositing Ga on Si, which was then treated with C. Ga has been shown to have a catalytic effect on the growth of graphene. This study focussed on examining the growth surface and the deposition of Ga on this. Si(001) was primarily...

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Bibliographic Details
Main Author: Werner, Katharina
Contributors: Stolz, Wolfgang (Dr. habil.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2015
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Summary:This study aimed at the deposition of graphene on Si(001) via CVD by depositing Ga on Si, which was then treated with C. Ga has been shown to have a catalytic effect on the growth of graphene. This study focussed on examining the growth surface and the deposition of Ga on this. Si(001) was primarily used as substrate, but as an intermixing of Ga and Si was observed, the usage of a GaP interlayer was also studied. Finally the deposition of C on Ga-pretreated Si and on GaP was investigated. Ga deposition was examined for the Ga precursors TEGa and TMGa. The results obtained for the precursors differ from each other due to the different reaction pathways for decomposition. For all utilized conditions Ga etches into Si, forming pyramidal structures. Mounds occur on the surface above these. The pyramidal structures exhibit boundaries on the Si{111} lattice planes due to the greater stability of these. The dimensions of the pyramidal structures and mounds are increased for TMGa compared to TEGa deposition. This might result from an organic layer formed by the residual groups on the Si surface for TEGa deposition. This might restrict the mobility of Ga. A preferential ordering of Ga aggregates at SB step edges was observed for low surface coverage. Like the preferential annihilation of Si vacancies at SB step edges, this might be caused by a change in the electronic structure at these particular step edges. Considerable intermixing of Ga and Si was observed for TMGa deposition, resulting in the growth of new crystalline Si structures at the edges of the Ga-containing structures during the sample cool-down. To prevent this intermixing a GaP interlayer was grown on Si(001) prior to Ga deposition. The stability of GaP at high temperatures and the GaP growth on Si(001) was examined. A GaP buffer on GaP(001) as well as a GaP layer on Si(001) remains intact during annealing in H2 at 50mbar and temperatures up to 800°C, without a stabilization. Earlier studies have shown that a high-quality growth of GaP on Si(001) is possible when a TBP preflow is applied. The precise processes at the interface were analyzed here. The usage of a sufficient amount of TBP led to an absence of Ga-containing aggregates for both Ga precursors. GaP growth at 450°C only occurred in combination with TEGa. TBP only decompose at 450°C in the presence of a catalyst such as TEGa. TMGa does not have a catalytic effect. As no Ga structures appear on the Si either for TMGa when a TBP preflow is used, the Si surface is presumably covered by a protective layer of TBP after the preflow. The TBP molecules preferentially order in rows perpendicular to the dimer rows on the Si(001) surface. This is probably due to H vacancies having a stabilized position on the next-row dimer next to a TBP molecule, constituting a favored adsorption site for further TBP molecules. Ga deposition on GaP(001) substrate and GaP on Si(001) was also studied for TEGa and TMGa. Here, too, Ga etches into the crystalline substrate and mounds form above the etched formations. For thin GaP layers on Si(001), Ga etches through the GaP and reaches the Si, forming pyramidal structures there. For thicker GaP layers and GaP substrates, less Ga diffuses into the GaP and structures with boundaries on lattice planes with a higher index than {111} form. An annealing of Ga-pretreated samples led to a disappearance of Ga at a temperature of 800°C. An annealing at a lower temperature results in a further intermixing of Ga with the substrate. No Ga was observed at the Si(001) surface after annealing, while on GaP metallic Ga is still present. Only samples with a GaP interlayer were therefore used for C deposition. A supply of C on Ga-pretreated samples led to etching of the initially existing Ga aggregates. This was observed for all C precursors studied, namely TBEthyne, TBEthylene and benzene, and most conditions applied. C deposition was therefore also studied on GaP surfaces without a prior deposition of Ga. Small amounts of C could be deposited at a growth temperature of 800°C, using the C precursor ethylene and H2 as carrier gas. Considerable amounts of material were deposited for the usage of N2 as carrier gas. But no signal induced by ordered C was detected by Raman spectroscopy, indicating that purely amorphous material was deposited. The most successful growth of C structures was achieved by supplying TBP during a high-temperature treatment of GaP. Considerable amounts of C were detected by SIMS and graphene-induced vibrational bands were found by Raman spectroscopy. No graphene layer was detected yet. However, a C containing layer exhibiting sp²-bonds was deposited for all conditions applied for a high-temperature treatment with TBP supply. As no sp²-bonded C atoms exist in the TBP molecule, these bonds must have formed during or after deposition. This could be used as starting point for further investigations of the deposition of graphene on Si(001).
Physical Description:156 Pages