研究目的
To investigate the enhancement of in-plane tensile strain in Ge epitaxial layers grown on Si-on-quartz wafers compared to those on Si-on-insulator wafers, for potential applications in photodetectors operating in the L band of optical communications.
研究成果
The research demonstrates that Ge epitaxial layers on SOQ wafers exhibit an enhanced tensile strain of 0.36±0.03%, which is 2–3 times larger than on SOI wafers, due to increased thermal expansion mismatch with the quartz substrate. This strain reduction in direct bandgap to 0.75 eV makes it suitable for photodetectors operating in the L band (up to 1.625 μm), advancing Si photonics applications.
研究不足
The study is limited to specific growth conditions and wafer types; potential limitations include the uniformity of Ge layers and the accuracy of strain measurements. Optimization could involve varying growth parameters or exploring other substrate materials.
1：Experimental Design and Method Selection:
The study involved growing Ge epitaxial layers on Si-on-quartz (SOQ) and Si-on-insulator (SOI) wafers using ultrahigh-vacuum chemical vapor deposition (UHV-CVD) with a two-step growth process at 370°C and 600°C. Theoretical calculations of tensile strain were performed based on thermal expansion coefficients.
2：Sample Selection and Data Sources:
SOQ wafers with a 160-nm-thick top (001) Si layer were fabricated by Shin-Etsu Chemical Co. Ltd. using a wafer bonding technique. Ge layers of 500 nm thickness were grown.
3：List of Experimental Equipment and Materials:
Equipment included a scanning electron microscope (SEM) for imaging, X-ray diffraction (XRD) at SPring-8 with a wavelength of
4：0827 nm for strain measurement, Raman spectroscopy for strain analysis, photoreflectance (PR) spectroscopy for bandgap measurement, and photoluminescence (PL) spectroscopy for optical characterization. Materials included SOQ and SOI wafers, and Ge for epitaxial growth. Experimental Procedures and Operational Workflow:
Ge layers were grown on SOQ and SOI wafers. Cross-sectional SEM images were taken. XRD mapping was conducted to measure in-plane strain. Raman spectra were obtained. PR and PL spectra were measured to determine direct bandgap energies and optical properties.
5：Data Analysis Methods:
Strain values were calculated from XRD and Raman data. Bandgap energies were derived from PR spectra using theoretical fitting. PL peaks were analyzed for wavelength shifts.
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