Ge Defect

In substoichiometric germanium oxides, Ge02 x, the insufficiency of oxygen atoms can result in the formation of oxygen-deficient defects. The most typical of these defects is the so-called E -center (-Ge=) defect, which can also be combined with OV located in its nearest neighborhood. The E -center and the E -OV combination exhibit peculiar optical properties considered in this subsection. 

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Fig. 4.10. Model clusters used for simulation of the -Ge= defect (E ) and the combined -Ge= and oxygen vacancy defect (E -OV). Terminal H atoms are not shown.

There are a lot of defects in the germanium-doped core. The paramagnetic Ge( ) defects, where n refers to the number of next-nearest-neighbour Ge atoms surrounding a germanium ion with an associate unsatisfied single electron, were first identified by Friebele et al. These defects are shown schematically in Fig. 8.3. 

A schematic of proposed Ge defects of germania-doped silica. 

The tetrahedrally bonded materials, such as Si and Ge, possess only positional disorder however, materials of this type exhibit high density of defect states (DOS). It is only with the addition of elements such as hydrogen and/or a halogen, typically fluorine, that the DOS is reduced to a point such that electronic device appHcations emerge. These materials contain up to - 10 atomic % hydrogen, commonly called hydrogenated amorphous siHcon (i -Si H). 

They form a monolayer that is rich in defects, but no second monolayer is observed. The interpretation of these results is not straightforward from a chemical point of view both the electrodeposition of low-valent Ge Iy species and the formation of Au-Ge or even Au Ge h compounds are possible. A similar result is obtained if the electrodeposition is performed from GeGl4. There, 250 20 pm high islands are also observed on the electrode surface. They can be oxidized reversibly and disappear completely from the surface. With Gel4 the oxidation is more complicated, because the electrode potential for the gold step oxidation is too close to that of the island electrodissolution, so that the two processes can hardly be distinguished. The gold step oxidation already occurs at -i-lO mV vs. the former open circuit potential, at h-485 mV the oxidation of iodide to iodine starts. 

In a non-stoichiometric crystcd, the lattice may have either excess charge or excess cations and/or anions situated in the lattice. Consider the semiconductor, Ge. It is a homogeneous solid and is expected to contain excess charge. The defect reactions associated with the formation of p-type and n-type lattices are ... 

Despite such limitations, plasma-deposited a-C(N) H films were found to be used in a number of applications. The stress reduction induced by nitrogen incorporation [12] and consequent adhesion improvement, allowed the development of a-C(N) H antireflective coatings for Ge-based infrared detectors [13]. It was also found that N can electronically dope a-C H films, and can strongly decrease the defect density, which gives prospects on its use as a semiconductor material [14]. Nitrogen incorporation was also found to decrease the threshold electric field in electron-field emission process [15], making possible the use of a-C(N) H films as an overcoat on emission tips in flat-panel display devices [16]. 

Arefian NA, Shokuhfar A, Vaezi MR, Kandjani AE, Tabriz MF (2008) Sonochemical synthesis of SnO/ZnO nano-Composite the effects of temperature and sonication power. In Ochsner A, Murch GE (eds) Defect and diffusion forum, vol 273-276, Diffusion in solids and liquids III., pp 34-39... 

The direct proof that H is present in certain centers in Ge came from the substitution of D for H, resulting in an isotopic energy shift in the optical transition lines. The main technique for unraveling the nature of these defects, which are so few in number, is high-resolution photothermal ionization spectroscopy, where IR photons from an FTIR spectrometer excite carriers from the ls-like ground state to bound excited states. Phonons are used to complete the transitions from the excited states to the nearest band edge. The transitions are then detected as a photocurrent. 

As in other semiconductors, H effectively neutralizes deep-level defects in Ge, but the structure of these centers has so far remained elusive and calls for further investigation. 

Just as Si—FI bonds and the corresponding vibrational spectra occur in silanes, so similar P—H, As—H, Ge—H, etc. bonds and bands occur in molecules of these materials suggesting that a similar insight into defect processes in these materials can occur through infrared studies. We do not know of such work in germanium, but work in the III-Vs is beginning to appear. 

It is known that hydrogen incorporated into Si subsequently exposed to ionizing radiation inhibits the formation of induced secondary point defect (Pearton and Tavendale, 1982a). For example, in both Si and Ge a number of electron or y irradiation induced defect states appear to be vacancy-related, and exposure of the Si or Ge to a hydrogen plasma (or implantation of hydrogen into the sample) prior to irradiation induces a degree of... 

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