研究目的
To analyze the band bending and charge characteristics at the GeO2/Ge interface using x-ray photoemission spectroscopy (XPS) to understand the impact on device performance and reliability in Ge-based CMOS technology.
研究成果
The research demonstrates that HF-last cleaned Ge surfaces tend to be p-type regardless of bulk conductivity. HPO and LOA treatments effectively passivate negatively charged interface traps in n-Ge/GeO2 interfaces and annihilate positive fixed charges in p-Ge/GeO2 interfaces, reducing band bending. Time-dependent XPS measurements reveal electron traps in thermally-grown GeO2, which are also passivated by HPO and LOA. Four types of charges (interface traps, fixed charges, hole traps, electron traps) influence band bending and device reliability, with quality-dependent variations.
研究不足
The study is limited by the inability to quantitatively evaluate charge densities of net hole and electron traps due to the distribution of charges along the GeO2 surface and low density, as well as limitations in sample current measurement accuracy. Environmental influences were minimized but not entirely eliminated during sample transfer.
1：Experimental Design and Method Selection:
The study uses XPS to measure band bending and charge characteristics at GeO2/Ge interfaces. The method involves monitoring shifts in Ge 3d and O 1s core-level spectra under x-ray irradiation to evaluate charge densities and trapping phenomena.
2：Sample Selection and Data Sources:
Both p-type (Na ~ 1.5–3.2 × 10^16 cm^-3) and n-type (Nd ~ 1.1–1.4 × 10^16 cm^-3) Ge substrates were used. Samples were chemically cleaned with methanol, diluted HCl, and diluted HF. GeO2 films were thermally grown under high pressure (70 atm, HPO-GeO2) or atmospheric pressure (1 atm, APO-GeO2), with some APO samples further annealed at 380°C in O2 (LOA-GeO2).
3：5–2 × 10^16 cm^-3) and n-type (Nd ~ 1–4 × 10^16 cm^-3) Ge substrates were used. Samples were chemically cleaned with methanol, diluted HCl, and diluted HF. GeO2 films were thermally grown under high pressure (70 atm, HPO-GeO2) or atmospheric pressure (1 atm, APO-GeO2), with some APO samples further annealed at 380°C in O2 (LOA-GeO2).
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: XPS chamber with monochromatic Al Kα x-ray source (1486.7 eV), calibrated using Au 4f7/2, Ag 3d5/2, and Cu 2p3/2 peaks. Ge substrates, chemicals for cleaning (methanol, HCl, HF), and equipment for thermal oxidation and annealing.
4：7 eV), calibrated using Au 4f7/2, Ag 3d5/2, and Cu 2p3/2 peaks. Ge substrates, chemicals for cleaning (methanol, HCl, HF), and equipment for thermal oxidation and annealing.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Cleaned Ge surfaces were oxidized to form GeO2 layers. XPS measurements were performed at a photoelectron take-off angle of 80° immediately after sample preparation to avoid environmental influence. Spectra were collected with minimal data step (0.05 eV) and averaged over multiple scans. Time-dependent measurements were conducted to observe peak shifts with prolonged x-ray irradiation.
5：05 eV) and averaged over multiple scans. Time-dependent measurements were conducted to observe peak shifts with prolonged x-ray irradiation.
Data Analysis Methods:
5. Data Analysis Methods: Shirley background subtraction was used for spectra. Ge 3d signals were fitted with Voigt functions for decomposition into components (e.g., Ge1+, Ge2+, Ge3+, Ge4+). Band bending was analyzed based on peak shifts, and charge neutrality equations were applied to interpret results.
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