Paving The Way To Dislocation Reduction In Ge/Si(001) Heteroepitaxy Using C-Based Strained Layer Superlattices
JOURNAL OF APPLIED PHYSICS(2020)
摘要
Epitaxial Ge films were grown on Si(001) substrates by molecular beam epitaxy. During epitaxial growth, two carbon interlayers were deposited at varying substrate temperatures (140 - 620mml:mspace width=".1emmml:mspace degreesC) and with varying C quantity (0 - 1.5 mml:mspace width=".1em"mml:mspacemonolayers). The influence of the second carbon interlayer on in-plane strain was investigated using high-resolution x-ray diffraction and transmission electron microscopy (TEM). All samples exhibited compressive strain, which was attributed to substitutional incorporation of carbon atoms. In-plane strain decreases with increasing substrate temperature during carbon deposition, indicating that enhanced surface mobility of carbon adatoms leads to formation of carbon clusters. This was confirmed by cross-sectional TEM investigations. Variation of C quantity at180mml:mspace width=".1em"mml:mspace degreesC reveals maximum strain at an intermediate quantity of 0.8 monolayers. Omission of the second C interlayer results in much lower strain, indicating a mismatch between the two Ge layers separated by a C interlayer. This could be used to enforce dislocation filtering following the principle of strained layer superlattices. An upper estimate of1 x10- 3 was found for the mismatch strain, resulting in a critical thickness for dislocation filtering ofh c = 153 mml:mspace width=".1em"mml:mspacenm. A sample just exceedingh c exhibited a clear dislocation reduction effect as shown by TEM.
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