Epitaxial Growth and Mobility Enhancement of Group IV Semiconductors by Chemical Vapor Deposition
Date Issued
2016
Date
2016
Author(s)
Huang, Shih-Hsien
Abstract
Group IV semiconductors such as SiGe, Ge and GeSn are attractive materials for the application of the metal-oxide-semiconductor field effect transistors and photonic devices due to their several benefits, such as the high carrier mobility, the possibility of achieving a direct bandgap, and the compatibility with conventional Si technology. In this dissertation, epitaxial growth and characterization of group IV semiconductor by chemical vapor deposition are investigated. In the first part of this thesis, the challenges of growing high quality epitaxial group IV semiconductors are discussed. The low temperature Ge layer is used to improve the surface roughness for Ge growth on Si. To improve the crystallinity and decrease the threading dislocation density, SiGe graded relaxed buffers, post-deposition annealing and laser annealing are proposed. In addition, in order to allow GeSn growth with high Sn concentration and avoid Sn segregation, Ge2H6 and SnCl4 are proposed as the precursors for the low temperature GeSn growth. After the discussion on the growth of high quality epitaxial group IV semiconductors, strained Si/SiGe heterostructures are grown and investigated for the high mobility of two-dimensional electron gas (2DEG). The dominant factors that limit the 2DEG mobility are further exploration. The dominant factors that limit the 2DEG mobility are Coulomb scattering of background charges, interface roughness scattering and threading dislocation scattering. The highest 2DEG mobility has reached 2.4 × 106 cm2 /V s by lowering background doping in the strained Si quantum well. In the third part of this thesis, high electron concentration and high tensile strained of phosphorus-doped Ge on Si(100) is investigated. The phosphorus incorporation by chemical vapor deposition and the activation by laser annealing reaches the electron concentration of ∼3 × 1020 cm−3. The pulsed laser not only activates the phosphorus but also produces the biaxial tensile strain of 0.35%. In addition, circular transmission line model and refined transfer length method are investigated to measure the contact resistivity of the sample with the electron concentration of ∼3 × 1020 cm−3. With the nickel germanide contact, the specific contact resistivity reaches as low as 1.5×10−8 Ω-cm2 by greatly reducing the tunneling distance. Finally, the material and thermal stability characteristics of strained GeSn layers is investigated. The Sn concentration, strain, and thickness are obtained by X-ray diffraction and transmission electron microscopy. The effects of oxidation temperature on GeSn material characteristics are further exploration during thermal process.
Subjects
Epitaxy
Chemical vapor deposition
Group IV semiconductors
2DEG mobility
Dopant activation
Contact resistivity
GeSn
Type
thesis