Formation and stability of germanium oxide induced by atomic oxygen exposure (original) (raw)
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Effect of Substrate Orientation on the Growth of Germanium Oxide in Dry Oxygen Ambience
IOP Conference Series: Materials Science and Engineering, 2017
The present investigation deals with the effect of substrate orientation effect on the growth of thermally oxidized Ge. The thermal oxidation was performed at temperature between 375 and 550°C in dry oxygen ambient under atmospheric pressure. The thickness of thermally oxidized Ge films was measured by spectroscopic ellipsometry and the chemical bonding structures were characterized by using x-ray photoelectron spectroscopy (XPS). No orientation dependence was observed for the oxidation at temperature of 375°C while for oxidation at 490 and 550°C, Ge oxidation and GeO desorption rate of (100) orientation yield higher rate than (111). The larger atomic space of (100) orientation explains the higher oxidation and desorption rate at Ge surface.
Impact of O2 exposure on surface crystallinity of clean and Ba terminated Ge(100) surfaces
Applied Surface Science, 2008
In analogy with the case of Sr on Si [Y. Liang, S. Gan, M. Engelhard, Appl. Phys. Lett. 79 (2001) 3591], we studied surface crystallinity and oxidation behaviour of clean and Ba terminated Ge(1 0 0) surfaces as a function of oxygen pressure and temperature. The structural and chemical changes in the Ge surface layer were monitored by LEED, XPS and real-time RHEED. In contrast to the oxidation retarding effect, observed for 1/2 monolayer of Sr on Si, the presence of a Ba termination layer leads to a pronounced increase in Ge oxidation rate with respect to clean Ge. In fact, while the Ge(1 0 0) surface terminated with 1/2 ML Ba amorphizes for a pO 2 of 10 À2 Torr, LEED indicates that clean Ge forms a thin (4.5 Å), 1 Â 1 ordered oxide upon aggressive O 2 exposure (150 Torr, 200 8C, 30 min). We briefly discuss the origins for the difference in behaviour between Ba on Ge and Sr on Si.
Native Oxides Formed on Single‐Crystal Germanium by Wet Chemical Reactions
Journal of The Electrochemical Society, 1988
The preparation of stable oxide films on single-crystal germanium surfaces by a room temperature "wet" chemical oxidation technique is described. Characterization by IR-transmission, eUipsometry, x-ray photoelectron spectroscopy, Rutherford backscattering, and electron microscopy show that such films are dense, uniform, and free of defects. The oxides are a mixture of two germanium dioxide phases both of which have a cristobalite atomic configuration. Unlike hexagonal germania, these films are stable in both water and hydrofluoric acid. They can be totally converted to the hexagonal dioxide phase by heat-treatment in either oxygen or nitrogen ambient at 600~ The growth kinetics, mechanisms and morphologies of the oxides formed by this method are presented. Preliminary evaluation of the electronic character of the oxide/semiconductor interface is also included.
Role of the Oxygen Content in the GeO2 Passivation of Ge Substrates as a Function of the Oxidizer
Journal of The Electrochemical Society, 2012
The electrical quality of the GeO 2 /Ge interface, prior to and after Gd 2 O 3 deposition, has been investigated as a function of the oxidizer (atomic O, O 2 , O 3) used for the GeO 2 based passivation of the Ge surface. In particular, the density of interface traps depends on the details of the Ge oxidation process and on the reactivity of the GeO 2 passivation layer with the overlying Gd 2 O 3 film. Complementary compositional depth profiling analysis shows that the oxygen content in the interfacial layer varies as a function of the type of oxidizer and plays a key role in dictating the interface chemistry and the electrical features of the MOS structures.
Pressure effect on the growth of oxide layers on germanium substrates
Journal of Electron Spectroscopy and Related Phenomena, 2001
X-ray Photoelectron Spectroscopy (XPS) was used to investigate the growth of thin oxide layers obtained by dry oxidation on (011 ) germanium substrates. The heat treatments were carried out, in-situ, at T53808C under various values of air pressure. The quantitative analysis of the XPS spectra suggests the growth of non uniform oxide layers. An apparent thickness of the oxide film was defined as function of the fraction of the oxidized surface and of the actual thickness of the oxide islands. The results show a quasi linear dependence of the apparent thickness versus the air pressure.
Native Oxidation Growth on Ge(111) and (100) Surfaces
Japanese Journal of Applied Physics, 2011
We studied the native oxide growth on Ge(100) and (111) surfaces treated by HCl and HF cleaning in clean room air by high-resolution X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The native oxidation of both HCl- and HF-last Ge(100) surfaces exhibited likely layer-by-layer fashion. The native oxide growth of the n-Ge(100) was significantly faster than the p-Ge(100) at the early stage of native oxidation. This can be explained by the formation of an O2- ion through free electron transfer from the Ge to the adsorbed O2 molecules, which induces the surface electric field that can initiate the oxidation. In the case of different crystallographic orientations, the oxide rate of the Ge(100) surface was faster than that of the Ge(111) surface. This might be attributed to larger open space of the Ge(100) surface than that of the Ge(111) surface.
Materials Today: Proceedings, 2019
The evolution of different oxidation states during thermal oxidation of (100) oriented Ge substrate was investigated with X-ray photoelectron spectroscopic analysis. The thermally grown oxides in the temperature range of 380 to 500 o C were found to consist of four different oxidation states of Ge, namely, Ge 1+ , Ge 2+ , Ge 3+ , and Ge 4+. The fractional composition of the oxide species is seen to be dependent on oxidation temperature. Spectroscopic depth profiling reveals variation of oxide composition along the depth of the oxide layer with a large concentration of GeO 2 near the oxide surface and a large concentration of suboxides near the oxide/Ge interface. The results obtained in the investigation will help in achieving greater insight into the thermal oxidation process of Ge.
An atomic view of Fermi level pinning of Ge(100) by O2
Surface Science, 2008
An experimental atomic-level study of the structural and electronic properties of the oxidation of the Ge(100) surface was performed using scanning tunneling microscopy (STM) and spectroscopy (STS). Room-temperature O 2 -dosed Ge(100) surfaces at sub-monolayer coverages (with and without post-oxidation annealing) were imaged via STM in order to identify the bonding geometries of the oxidation reaction products, and STS spectra were taken for the characterization of the surface electronic structures resulting from those structures. DFT modeling, including STM simulations, was performed for the various potential adsorbate structures indicated by STM imaging in order to elucidate the most likely bonding geometries. Long, low-temperature post-oxidation anneals (325°C) were used to eliminate some metastable oxidation reaction products and to drive the coalescence of the stable products. The O 2 -reacted Ge(100) surfaces, both the disordered pre-annealed and the ordered post-annealed (325°C), were found to exhibit Fermi level pinning near the valence band. However, proper Fermi level position was restored upon desorption of the GeO at 500°C, indicating that the presence of germanium suboxide at the Ge(100) surface is a source of Fermi level pinning for annealed surfaces. The pinning observed on the room-temperature as-oxidized surface is most likely also due to the suboxide coverage; it is likely that additional components to the pinning states also arise from the displaced Ge ad-species.
Interactions of germanium atoms with silica surfaces
Applied Surface Science, 2005
GeH 4 is thermally cracked over a hot filament depositing 0.7-15 ML Ge onto 2-7 nm SiO 2 /Si(1 0 0) at substrate temperatures of 300-970 K. Ge bonding changes are analyzed during annealing with X-ray photoelectron spectroscopy. Ge, GeH x , GeO, and GeO 2 desorption is monitored through temperature programmed desorption in the temperature range 300-1000 K. Low temperature desorption features are attributed to GeO and GeH 4. No GeO 2 desorption is observed, but GeO 2 decomposition to Ge through high temperature pathways is seen above 750 K. Germanium oxidization results from Ge etching of the oxide substrate. With these results, explanations for the failure of conventional chemical vapor deposition to produce Ge nanocrystals on SiO 2 surfaces are proposed.