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Title: Surface passivation and high-k dielectrics integration of Ge-based FETs: First-principles calculations and in situ characterizations.
Authors: YANG MING
Keywords: Ge-FETs, surface passivation, high K dielectric
Issue Date: 1-Jul-2009
Citation: YANG MING (2009-07-01). Surface passivation and high-k dielectrics integration of Ge-based FETs: First-principles calculations and in situ characterizations.. ScholarBank@NUS Repository.
Abstract: Surface passivation and high-K dielectrics integration are two critical issues for fabricating high performance Ge-based CMOS devices. In this presentation, we will present result of first-principles calculations and experimental characterizations on these two issues.Stoichiometric GeO2 dielectrics with good quality were grown on Ge (001). Their band alignments and interface stability with/without nitrogen incorporation have been studied. The calculated PDOS indicates that oxygen and Ge vacancies cause the reduction of VBO at reduced GeOx/Ge(001) interface, which clarified the large difference of VBOs determined by different methods.First-principles calculations were carried out to study electronic, optical, and intrinsic defect properties of bulk Ge3N4. The results show that nitrogen vacancies would be the main source of intrinsic defects due to their low formation energies. It was also found that the lattice constant of beta-Ge3N4 matches well with that of Ge (111) surface. Two interface structures were proposed for beta-Ge3N4 (0001)/Ge (111), and the calculated interface formation energies indicate that the interface structure without dangling bonds are much more energetically favorable. The calculated VBO and CBO at the stable interface are 1.23 and 2.10 eV, respectively. Experimentally, crystalline Ge3N4 were grown on Ge (111) substrate using atomic source nitridation. The measured band offsets are consistent with theoretical predictions.High K dielectrics SrZrO3 were prepared on Ge (001) substrate by using PLD. The corresponding VBO and CBO were measured by XPS to be 3.26 eV and 1.77 eV, respectively. The SrZrO3 on Ge substrate remains stable after annealing at centigrade of 600 degree, but the HRTEM images indicate that the amorphous SrZrO3 would become polycrystalline after annealing. Theoretically, various interface structures of cubic SrZrO3 (001)/Ge (001) were proposed. The calculated interface formation energies show that Zr-O terminated interface is more stable in oxygen rich ambient. This suggests that to grow a monolayer of ZrO2 on Ge surface might be favorable to epitaxially grow SrZrO3. It was also found that oxygen chemical potential would affect the band offsets and interface stability greatly.
Appears in Collections:Ph.D Theses (Open)

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