Epitaxial Growth of Germanium on GaAs substrates by UHVCVD for Post P-Channel and CMOS Applications
| Autor: | Tang, Shih Hsuan, 唐士軒 |
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| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 High-quality epitaxial Ge films were grown on GaAs substrates by ultra high vacuum chemical vapor deposition (UHVCVD). High crystallinity and smooth surface were observed for these films by X-ray diffraction, transmission electron microscopy and atomic force microscopy. Direct band gap emission (1550nm) from this structure was detected by photoluminescence. Valence band offset of 0.16 eV at the Ge/GaAs interface was measured by XPS. N-type arsenic self-doping of 1018/cm-3 in the grown Ge layers was determined using electrochemical capacitance voltage measurement. Epitaxial germanium metal-oxide-semiconductor capacitors (MOSCAP) were also fabricated on GaAs substrate using atomic layer deposited Al2O3 gate dielectric with surface treatments including pure HF and HF plus rapid thermal oxidation (RTO). The electrical characteristics of 10 nm Al2O3/Ge MOSCAP showed p-type behavior with excellent C-V responses and low leakage current. Interface state density in the order of 1011 eV-1cm-2 was determined from the conductance method and the HF plus RTO treatment exhibits better Al2O3/Ge interface quality than that of pure HF treatment. Epitaxial Ge films were also grown on GaAs (100), (110) and (111) substrates by using ultra-high vacuum chemical vapor deposition and studied with various methods. The incubation times and growth rates were quite different for these three GaAs substrates because the surface arsenic coverage on GaAs and hydrogen desorption energy on Ge are different for each orientation. High-resolution x-ray diffraction measurements, direct band-gap emission of photoluminescence measurements, and cross-sectional transmission electron microscopy showed that the Ge films had high crystal quality, low defect density and sharp Ge/GaAs interfaces. Our atomic force microscopy analysis found that the Ge films grow on GaAs (100) and (111) via the Frank van der Merwe mode, while the Ge film grows on GaAs (110) via the Volmer-Weber mode at the initial growth stage, which can be explained by the thermodynamic theory of capillarity. Interestingly, when the thickness of the Ge film on the GaAs (110) substrate increases to ~ 220 nm, the 3D Ge islands merge and form a smooth surface (rms roughness of 0.3 nm), which is useful for devices. We also fabricated Ge metal-oxide-semiconductor capacitors (MOSCAPs) on GaAs (100) and (110) substrates. Both Ge/GaAs (100) and Ge/GaAs (110) MOSCAPs exhibit good capacitance-voltage responses with strong inversion behaviors, which means the grown material has reached device quality. The Ge/GaAs (110) structure especially offers optimal integration of Ge pMOSFETs on GaAs substrates because Ge (110) has a high hole mobility compared with Ge (100) and (111). |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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