Germanium surface cleaning, passivation, and initial oxidation.

摘要

Germanium (Ge) is an attractive material to be incorporated into Si-based electronic devices because of its higher intrinsic low field carrier mobility. In order to fabricate devices using Ge, it is essential to understand the Ge surface chemistry and find an effective way to clean and passivate its surface. Systematic studies of these processes had not been performed prior to this work. In this work, synchrotron radiation photoelectron spectroscopy and atomic force microscopy are used to investigate the Ge surface cleaning, passivation, morphology and initial oxidation. In addition, other materials closely related to Ge are characterized.; The wet chemical cleaning and passivation of Ge surfaces are first studied. The etching mechanism determines the surface passivation. HF etching leads to rougher, hydrophobic, hydrogen passivated surfaces, and the hydrogen coverage is a function of the HF concentration. In contrast, HCl (HBr) etching results in smoother, hydrophilic, chlorine (bromine) passivated surfaces. Results from substrates with different orientations are compared, and the similarity and difference between Ge and Si are discussed.; The thermal stability of passivated Ge surfaces is probed by vacuum annealing. As the annealing temperature increases, the passivation layers desorb gradually from the surfaces, and surface states are formed. The thermal stability of different passivation layers is compared, and the influence of substrate orientations is stressed.; The passivated Ge surfaces are not stable in air at room temperature. Therefore, controlled experiments are performed to derive the initial oxidation mechanism. The stability of passivated surfaces relies on the coverage of the passivation layers, the size of the passivating atoms, the amount of hydroxide left on the surface after etching, and the difficulty of replacing the passivation layers.; Finally, other materials closely related to Ge are characterized. Results on strained Si and Si1-xGex surfaces show that the introduced strain does not alter the Si surface chemistry significantly, while the addition of Ge changes the Si surface chemistry dramatically. Both strained Si and Si1-xGex surfaces have enhanced oxidation rates. In addition, Ge nanowires have similar surface chemistry to Ge planar wafers, and a very nonstoichiometric GeO, layer exists at the HfO2/Ge(100) interface.