研究目的
Investigating the reduction of threading dislocation density (TDD) in Ge layers selectively grown on Si with semicylindrical voids on SiO2 masks.
研究成果
The study demonstrates a new approach to reduce TDD in Ge epilayers on Si using semicylindrical voids formed through SEG and coalescence. TEM observations confirm the termination of TDs at voids and the suppression of 2D defects, achieving a large TD-free area. Further reductions in TDD are possible with optimized growth conditions.
研究不足
The study is limited by the resolution of the electron beam lithography system used, which affects the minimum widths of growth windows and SEG masks. The maximum process temperature is constrained to 700°C to prevent Si-Ge intermixing and P dopant out diffusion.
1：Experimental Design and Method Selection
The study employs selective epitaxial growth (SEG) technique to form Ge layers with semicylindrical voids over SiO2 masks on Si substrates. Cross-sectional and plan-view transmission electron microscope (TEM) observations are used to analyze the defects and their reduction.
2：Sample Selection and Data Sources
B-doped p-Si (001) substrates with thermally oxidized SiO2 layers patterned into line-and-space stripes are used. The samples include both coalesced Ge layers and blanket Ge layers for comparison.
3：List of Experimental Equipment and Materials
Ultrahigh-vacuum chemical vapor deposition chamber, GeH4 source gas, JEM-2010HC TEM (JEOL, Japan), focused Ga ion beam (FIB) for TEM specimen preparation.
4：Experimental Procedures and Operational Workflow
The process involves thermal oxidation of Si substrates, patterning of SiO2 masks, Ge epitaxial growth at 700°C, and TEM specimen preparation via FIB micro sampling and ion milling. TEM and STEM observations are conducted to analyze the Ge layers.
5：Data Analysis Methods
TEM and STEM images are analyzed to observe the termination of threading dislocations at semicylindrical voids and the suppression of two-dimensional defects. TDD is quantified from plan-view TEM images.
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