Oxygen In Germanium Research Articles

Defect characteristic of oxygen-deficient Ge-doped preform using photoluminescence spectroscopy

Study has been made of the Photoluminescence properties of Ge-doped silica preforms fabricated using the MCVD process and subsequently subjected to γ-ray irradiation. The photoluminescence emissions pointed to the presence of defects related to oxygen vacancies. Two types of preform were fabricated, obtained using a different flow rate and deposition temperature for each case. Results from the absorption spectra of the samples named as P1 and P2, show a signature absorption peak at 5.1 eV and 6.8 eV, indicative of oxygen-deficient and oxygen-rich defects respectively. Photoluminescence investigation have been carried out before and after the irradiation process with both samples reveal two main peaks at 1.5 eV. The highest intensity at 1.5 eV is known as an interaction between the Non- Bridging Oxygen Hole Centre (NBHOC) with the presence of impurity in the glass matrix. Upon irradiation, weak peak can be observed at 1.8 eV, sample P1 and P2, the PL intensity increases by a factor of 20 × and 50 × , respectively. This peak is associated with the oxygen deficient state in the sample. The peak referring to defect known as Germanium Lone Pair Centre (GLPC) are observed in both samples, peak shown at 3.1 eV, regardless of the Germanium Oxygen Deficient Centre (GODC) content. In regard to this, it can be concluded that this defect is generated independently in all germanium samples and are not correlated with the GODC band observed in the absorption band.

Development of a ReaxFF Reactive Force Field for Interstitial Oxygen in Germanium and Its Application to GeO2/Ge Interfaces

We developed the ReaxFF force field parameters for Ge/O/H interactions, specifically targeted for the applications of Ge/GeO2 interfaces and O-diffusion in bulk Ge. The original training set, taken...

Indiffusion of oxygen in germanium induced by pulsed laser melting

A systematic study of the indiffusion of oxygen in germanium induced by pulsed laser melting (PLM) is reported. In order to evidence the impact of the experimental parameters, different processing conditions have been compared, i.e. with or without pre-PLM etching of the Ge native oxide by H2O or HF dip, Air or N2-rich atmosphere, and single or multi-pulse PLM. Oxygen indiffusion is always observed with surface concentration above 1 × 1019 cm−3 for all the processing conditions. Pre-PLM surface chemical treatments seem to have no significant influence in terms of the oxygen penetration, although HF allows lower surface roughening. On the contrary, a processing atmosphere with reduced oxygen concentration is more efficient in reducing the overall O indiffusion. The present experimental results are crucial in view of the implementation of the PLM technique for highly doped Ge as well as to design studies where contamination issue might be crucial.

Synthesis, Structure, and Reactivity of Carboranyl‐Supported Germylenes: Approaching Germanones

Two iminocarboranyl germylenes, 1,2‐[C(tBu)=N(Dipp)Ge(Cl)]‐1,2‐C2B10H10 (2) (Dipp = 2,6‐iPr2C6H3) and [1‐{C(tBu)=N(Dipp)}‐1,2‐C2B10H10]2Ge (3), have been prepared and structurally characterized. The reaction of 2 with Me3NO or S8 afforded the germanium oxygen‐ or sulfur‐bridged dimer [1‐{C(tBu)=N(Dipp)‐1,2‐C2B10H10}Ge(µ‐O)(Cl)]2 (4) or [1‐{C(tBu)=N(Dipp)‐1,2‐C2B10H10}Ge(µ‐S)(Cl)]2 (5) containing a four‐membered Ge2O2 or Ge2S2 ring, respectively. On the other hand, the reaction of 2 with K[CpFe(CO)2] led to the isolation of an iron–germylene compound featuring a Ge–Fe σ bond, 1,2‐{C(tBu)=N(Dipp)Ge[Fe(Cp)(CO)2]}‐1,2‐C2B10H10 (6). All new compounds were characterized by multiple NMR spectroscopic techniques and single‐crystal X‐ray analysis.

Diffusion of interstitial oxygen in silicon and germanium: a hybrid functional study

The minimum-energy paths for the diffusion of an interstitial O atom in silicon and germanium are studied through the nudged-elastic-band method and hybrid functional calculations. The reconsideration of the diffusion of O in silicon primarily serves the purpose of validating the procedure for studying the O diffusion in germanium. Our calculations show that the minimum energy path goes through an asymmetric transition state in both silicon and germanium. The stability of these transition states is found to be enhanced by the generation of unpaired electrons in the highest occupied single-particle states. Calculated energy barriers are 2.54 and 2.14 eV for Si and Ge, in very good agreement with corresponding experimental values of 2.53 and 2.08 eV, respectively.

A new high-pressure strontium germanate, SrGe2O5.

The Sr-Ge-O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca-Si-O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3 high-pressure perovskite phase is the first Ge-based transparent electronic conductor make the Sr-Ge-O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high-pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co-existent phase with SrGeO3 perovskite single crystals in the sample recovered in the compression experiment of SrGeO3 pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium-oxygen framework layers stacked along [001], with Sr atoms located at the 12-coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6 octahedra and between GeO6 octahedra and GeO4 tetrahedra. The present SrGe2O5 is thus isostructural with the high-pressure phases of SrSi2O5 and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6 and GeO4 polyhedra to cation substitution at the Sr site are much less than that of the SrO12 cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.

The influence of impurity and isotopic composition of single-crystal germanium on optical transmission in the range of 520–1000 cm−1

The optical properties of pure and doped germanium single crystals of natural isotopic composition and isotopically pure 70Ge and 74Ge single crystals have been investigated. The influence of dopants and the presence of residual oxygen in germanium on the position and shape of phonon absorption peaks and on the attenuation coefficients for these peaks in the spectral range of 520–1000 cm−1 is experimentally revealed. The decrease in the frequency of peaks in phonon absorption bands with an increase in the mass number of germanium isotopes is analyzed.

On the germanium–oxygen coordination number in lead germanate glasses

Knowledge of the Ge–O coordination number, nGeO, in germanate glasses is of paramount importance for understanding the germanate anomaly and relating the glass structure to its thermophysical properties. By careful measurement using high resolution neutron diffraction on two samples of 40PbO.60GeO2 glass, it is clearly demonstrated that the average Ge–O coordination number, nGeO, is much less than the value, 4.77(5), previously obtained by use of neutron diffraction [Umesaki et al., Physica B 213 (1995) 490]. However, it is also clear that nGeO is still significantly greater than four (~4.1), and this is supported by the observed asymmetry of the Ge–O peak in the real-space total correlation functions. The average Pb–O coordination number is a little in excess of three, typical of Pb2+ with a sterically active lone-pair of electrons.

Luminescence of unfused 95%SiO2–5%GeO2 amorphous films with fluorine additive: No evidence for presence of GeODC(I) defects found

Photoluminescence (PL) of unfused amorphous germanosilicate films with fluorine additive is studied in 2–8.5eV spectral range. Experiments are based on films deposited on silica substrates by means of the surface-plasma chemical vapor deposition (SPCVD). Films of about 100μm in thickness with “high F” (~4.2wt.%) and “low F” (~0.5wt.%) fluorine content have been fabricated for the experiments. KrF (248nm), ArF (193nm) and F2 (157nm) excimer lasers are used to pump PL. It is found that absorption and luminescence associated with germanium oxygen deficient centers (GeODCs) in “high F” and “low F” films differ. In the “high F” unfused film absorption coefficient of the band at 5eV as well as intensity of the blue PL band at 3.1eV are significantly greater. This film proves features of the so called GeODCs(II), which symbolize twofold coordinated germanium defects in silica network. In the “low F” unfused film absorption band at 5eV is feebly marked. Poorly resolved PL intrinsic to GeODCs(II) can be detected in this film under the KrF laser pump. The most significant PL features are revealed under deeper UV pump by ArF and F2 lasers. Spectral positions of PL bands excited by these lasers correspond to GeODCs(II). However PL decay kinetics dramatically differs from that one intrinsic to GeODCs(II). Noticeable growth of PL intensity caused by permanent (half an hour and more) exposure to ArF and/or F2 lasers takes place, indicating GeODC(II) formation. It is found that considerable body of fluorine additive has the same effect as profusion for “low F” and/or fluorine free germanosilicate amorphous material synthesized by SPCVD. In the “high F” film yield of GeODC(II) PL pumped by the F2 laser remains high. This speaks for the suppression of the competitive 7.6eV absorption band associated with SiODCs(I) by fluorine additive indicating a decrease in the content of this type of defects in the material. High yield of GeODC(II) luminescence pumped by deep UV photons as well as hypothetical similarity of SiODC(I) and GeODC(I) permit one to conclude that GeODCs(II) are the only defects dominating in the materials under study.

Interaction of n-type dopants with oxygen in silicon and germanium

Density functional theory calculations are employed to gain a fundamental insight on the interaction of n-type dopants such as phosphorous and arsenic with oxygen interstitials and A-centers (vacancy-oxygen interstitial pairs) in silicon and germanium. We propose the formation of the phosphorous-vacancy-oxygen interstitial and arsenic-vacancy-oxygen interstitial cluster in both silicon and germanium.

Defect configurations of high-k cations in germanium

At germanium/high-k interfaces cations and oxygen interstitials can diffuse into the germanium substrate. Here we employ density functional theory calculations to investigate the interaction of a range of such cations (Al, Y, Zr, Nb, La, and Hf) with intrinsic defects and oxygen in germanium. It is predicted that high-k cations strongly bind with lattice vacancies, oxygen interstitials, and A-centers. The implications for microelectronic device performance are discussed.

A-centers and isovalent impurities in germanium: Density functional theory calculations

Abstract In the present study density functional theory calculations have been used to calculate the binding energies of clusters formed between lattice vacancies, oxygen and isovalent atoms in germanium. In particular we concentrated on the prediction of binding energies of A-centers or oxygen interstitials that are at nearest and next nearest neighbor sites to isovalent impurities (carbon, silicon and tin) in germanium. The A-center is an oxygen interstitial atom near a lattice vacancy and is an important impurity-defect pair in germanium. In germanium doped with carbon or silicon, we calculated that most of the binding energy of the cluster formed between A-centers and the carbon or silicon atoms is due to the interaction between the oxygen interstitial atom and the carbon or silicon atoms. For tin-doped germanium most of the binding energy is due to the interaction of the oversized tin atom and the lattice vacancy, which essentially provide space for tin to relax. The nearest neighbor carbon–oxygen interstitial and the silicon–oxygen interstitial pairs are significantly bound, whereas the tin–oxygen interstitial pairs are not. The results are discussed in view of analogous investigations in isovalently doped silicon.

Decay mechanism of theν3865 cm−1vibration of oxygen in crystalline germanium

The nu(3) (862.5 cm(-1)) vibration of oxygen in crystalline germanium is shown to decay into one nu(1) local mode of the oxygen center plus two lattice modes. This description predicts increases in the linewidths in O-16-doped germanium, and decreases in the linewidths in O-18-doped germanium, as the Ge mass in the Ge-O-Ge complex increases, in agreement with observation. The decay time is expected to vary only slightly with the isotope of oxygen, as observed, and the smallest reported linewidths are consistent with the measured decay times.

Application of UV laser induced Ge-oxygen defect fluorescence for fibre characterisation

A new technique to monitor germanium oxygen deficiency centre defects (GeODC) and their relation to the refractive index profile in Ge-Si optical fibre have been developed. This method is based on UV excited luminescence of GeODC in silica based optical fibres. The GeODC defect profiles are unique to the fibre refractive index (profile of GeO2) and method of fibre making.

Effect of processing parameters on control of defect centers associated with second-order harmonic generation and photosensitivity in SiO2:GeO2 glass preforms

In this research, the effect of the H2/O2 ratio and the processing temperature parameters on the inducing and enhancement of the defect centers associated to the second-order optical non-linearity in SiO2:GeO2 glass preforms, prepared by vapor-phase axial deposition method, have been investigated. The formation of germanium oxygen deficient centers and the development of paramagnetic structures induced in the glass preforms after X-ray irradiation were investigated using UV–Vis absorption spectroscopy and electronic spin resonance. The results indicate that the concentration of germanium oxygen deficient centers increases exponentially when the H2/O2 ratio decreases, while the processing temperature increases, simultaneously. The electronic spin resonance spectra profiles, shows that defects of the electron trapped centers type [Ge(1), Ge(2)] are induced by the effect of X-ray irradiation. An efficient generation of defect centers associated to the second-order optical non-linearity in SiO2:GeO2 glass preforms, occurring in samples prepared with low H2/O2 ratios and high processing temperatures, have been observed.

Simulation of point defect diffusion in germanium

First results are presented of the simulation of the thermodynamic properties of intrinsic point defects and interstitial oxygen in single crystal germanium. The results are based on molecular dynamics calculations using a Stillinger–Weber potential and on the Einstein equation. Two different molecular dynamics codes are used and compared. A novel molecular dynamics algorithm was implemented, which allows describing the migration path of interstitial oxygen without assumptions on saddle point and positions of neighbouring atoms.

Vacancy defect reactions associated with oxygen and bismuth in irradiated germanium

Defect reactions occurring in Ge:Bi, O crystals upon electron and gamma irradiations at room temperature and the following isochronal annealing in the temperature range 80–350 °C have been studied by means of deep level spectroscopy (DLTS) and high-resolution Laplace DLTS. It is shown that bismuth and oxygen impurity atoms are the most effective traps for mobile vacancies created by irradiation in the crystals. Both the vacancy–oxygen (VO or A center) and vacancy–bismuth (Bi–V or E center) defects in Ge have three charge states and introduce two energy levels into the gap. The ratio of concentrations of the VO and Bi–V centers in as-irradiated samples depends on the relative concentrations of interstitial oxygen (O i) and substitutional bismuth (Bi s) atoms. Annealing studies demonstrate that in the temperature range 120–150 °C the concentration of the Bi–V center increases. This has been associated with the dissociation of VO that occurs in the range 100–150 °C. In consequence the proposed mechanism is the release of vacancies from the A center which are subsequently trapped by the Bi impurity atoms to form the Bi–V E center. It is suggested that the enhanced disappearance of the Bi–V centers in electron-irradiated oxygen-rich Ge samples is associated with the interaction of the E centers with mobile Ge self-interstitials released from oxygen-related traps at T ⩾ 1 4 0 ° C .

Fabrication and ultraviolet photosensitivity of Ge-doped silica films using FHD for optical waveguide

UV photosensitivity of Ge-doped silica films deposited on Si (1 0 0) substrates using flame hydrolysis deposition (FHD) has been investigated. The ratio of Ge and Si of the sample was estimated by XPS as 10:90, and it was shown by AFM as smooth and homogeneous. It seems to have not germanium oxygen deficiency centers which play a role in the change in refractive index after UV irradiation. The irradiation of a H 2-unloaded and a loaded film with fluency of 190 mJ/cm 2/pulse at 10 Hz to KrF excimer laser induced a relative value of the refractive index change of 5.46×10 −4 and 2.94×10 −3 at 1550 nm, respectively. Optical absorption and PL spectra of our FHD H 2-loaded sample demonstrate that Ge 2+ center (constituting GeO defect) was produced by a reaction of the germanosilicate glasses with the H 2 molecule, which could lead the higher UV-induced refractive index change after irradiation. Therefore, H 2 loading is sufficient to significantly increase the photosensitivity of Ge-doped SiO 2 film to 248 nm light.

General Model of Diffusion of Interstitial Oxygen in Silicon, Germanium and Silicon - Germanium Crystals

A theoretical modelling of the oxygen diffusivity in silicon, germanium and Si1-xGex (O) crystals both at normal and high hydrostatic pressure has been carried out using molecular mechanics, semiempirical and ab initio methods. It was established that the diffusion process of an interstitial oxygen atom (Oi) is controlled by the optimum configuration of three silicon (germanium) atoms nearest to Oi. The calculated values of the activation energy Ea (Si) = 2.59 eV, Ea(Ge) = 2.05 eV and pre-exponential factor D0(Si) = 0.28 cm2 s−1, D0(Ge) = 0.39 cm2 s−1 are in good agreement with experimental ones and for the first time describe perfectly the experimental temperature dependence of the Oi diffusion constant in Si crystals (T = 350–1200 °C). Hydrostatic pressure (P ≤ 80 kbar) results in a linear decrease of the diffusion barrier (∂P Ea (P) = −4.38 × 10−3 eV kbar−1 for Si crystals). The calculated pressure dependence of Oi diffusivity in silicon crystals agrees well with the pressure-enhanced initial growth of oxygen-related thermal donors. The simulation (PM5) has revealed that in Si1-xGex crystals there are two mechanisms of variation of Oi diffusion barrier. The increase of lattice constant leads to the linear increase of the diffusion barrier. Strains around Ge atoms decrease the diffusion barrier. Formation of gradient of diffusion barrier in the volume of Si1-xGex may be responsible for the experimentally observed suppression of generation of TD in Si1-xGex (O) crystals.

Dependence of H 2/O 2 ratio and GeO 2 content on the enhancement of second-order non-linearity related defects in Ge-doped optical fiber preforms

In this research, we studied the influence of the process conditions through the H 2/O 2 ratio and the GeO 2 content, on the formation of germanium oxygen deficient centers and paramagnetic defects center induced by X-ray irradiation in SiO 2:GeO 2 glass preform prepared by the vapor-phase axial deposition method. The absorption band at around 5.1 eV, characteristic of germanium oxygen defect center was observed in all glass preform sample absorption spectra. The absorption coefficient increased when the GeO 2 concentration increased, however, the absorption was higher in samples prepared with high H 2/O 2 ratio. The electronic spin resonance spectrum profiles suggest that paramagnetic structures, such as, electron trapped centers and positively charged germanium oxygen deficient centers, assigned as Ge(1) and Ge(2), respectively, are induced in all samples after being X-ray irradiated for 1 h. It was found that the concentration of induced paramagnetic centers is linearly proportional to germanium oxygen defect center concentration and that the efficiency in the enhancement of paramagnetic defect centers associated with second-order optical non-linearity increased as H 2/O 2 ratio used in the fabrication process was decreasing. It was concluded that SiO 2:GeO 2 glass preform with low H 2/O 2 ratio and higher GeO 2 content must be prepared for the enhancement of the second-order non-linearity.