Gold-doped Germanium Research Articles

Comparative research of configuration, stability and electronic properties of cationic and neutral [AuGen]λ and [Gen+1]λ (n=1-13, λ=0, +1) nanoalloy clusters

The configuration, stability, evolution, and electronic properties of neutral and cationic [AuGen]λ and [Gen+1]λ (n=1−13, λ=0, +1) nanoalloy clusters have been systematically investigated by using unbiased global search technique married with double-density functional strategy. The results reveal that although the neutral and cationic global minimal structures of gold-doped germanium clusters differ from each other when n=4, and 6–13, the evolution patterns are consistent. Attaching structures have been changed to Au-encapsulated motif at the turning point of n=11. The analyses of electronic structure and binding energy indicate that doping of an Au atom may decrease the stability of neutral Ge nanoclusters, but can enhance the stability of cationic Ge nanoclusters. The analyses of electronic property show that ionization potentials (IP) of Gen+1 cluster are larger than those of AuGen nanoalloy clusters, indicating that doping of an Au atom can decrease the ionization potential of neutral Ge nanoclusters. The analyses of HOMO and LUMO energy reveal that HOMO-LUMO gaps of neutral AuGen (n=1−13) with the exception of n=2 and 3 are smaller than that of Gen+1 clusters. For cations, the HOMO-LUMO gaps of [AuGen]+ are wider than that of [Gen+1]+ cluster when n=2, 5–7, and 9–11, narrower when n=3, 4, 8 and 13, and nearly identical when n=1 and 12. The PBE-DFT based global descriptors viz. Electronegativity, Hardness, Softness and Electrophilicity Index of [Gen+1]λ and [AuGen]λ (λ=0, +1; n=1−13) nanoclusters are estimated by means of HOMO-LUMO gap. And they possess highly correlation with HOMO-LUMO gap. The agreement between theoretical and experimental results such as IP, binding energy, HOMO-LUMO gap, and bond distance demonstrate the success of the computational analyses in this work.

Electronic structure and stability of anionic AuGen (n = 1–20) clusters and assemblies: a density functional modeling

In the present study electronic structure and stabilities of cationic gold-doped germanium clusters, AuGen (n = 1 to 20), and their assemblies have been investigated by density functional theory (DFT) modeling. Computational results show a good relationship between the thermodynamic parameters, average binding energy, embedding energy, fragmentation energy, etc., with the percentage hybridization between different Ge 4s, Ge 4p, and Au 5d atomic orbitals, which plays a dominating role in the stabilization of anionic AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Other thermodynamic and chemical parameters are also found consistent with the observed thermodynamic stabilities of the nanoclusters. In smaller size range (n < 11), Au atom always absorbs on the surface or vertex of pure Ge cluster. From n = 11, endohedral doping starts. In the assembled clusters, Au atom play the role as a bridging atom in Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Stability of the AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 are explained using magic number in shell-filled model and mixed (π-σ) aromatic rule. As per the symmetry and structure of AuGe12 cluster, it is comparable to a nido-cluster, and hence, its stability is explained using Wade-Mingos rule. Calculated VDE, ADE, HOMO-LUMO gap, and VIP have very close agreement with the experimental results. IR and Raman frequencies show that the vibration nature of the clusters could produce electromagnetic radiation in the far infrared region which is useful for medical applications.

Structure, stability and electronic property of the gold-doped germanium clusters: AuGe n (n = 2–13)

The structure, stability and electronic property of the AuGe n (n = 2–13) clusters with different spin configurations are systematically investigated with density-functional theory approach at UB3LYP/LanL2DZ level. In examining the lowest energy structures, it is found that the growth behaviors for the small-sized AuGe n (n = 2–9) clusters and relatively large-sized AuGe n (n = 10–13) clusters are different. As the number of Ge atom increases, the Au atom would gradually move from convex to surface and to interior sites. For the most stable structures of AuGe n (n = 10–13) clusters, the Au atom would be completely surrounded by the Ge atoms to form Au-encapsulated Ge n cages. Natural population analysis shows that the charges always transfer from the Au atom to the Ge n framework except for the AuGe2 cluster. This indicates that the Au atom acts as electron donor even the 5d orbitals of the Au atom are not significantly involved in chemical bonding. The analyses of the average atomic binding energies as well as the dissociation energies and the second-order differences of total energy show that the AuGe n clusters with n = 5, 9 and 12 are more stable than their neighboring ones, in which the bicapped pentagonal prism AuGe12 in D 2d symmetry is most stable. The highest occupied molecular orbital–lowest unoccupied molecular orbital gaps are explored to be in the region of semiconductors and the more stable clusters have slightly smaller gaps. It could be expected that the stable clusters might be considered as the novel building blocks in practical applications, e.g., the cluster-assembled semiconductors or optoelectronic material.

Negative differential conductivity and recombination instability of current in p-Ge(Au) in two-parametric space

We present the results of an experimental study of p-Ge(Au) samples and we compare these qualitatively with data furnished by the one-dimensional theoretical model developed to account for the recombination instability in gold-doped germanium in the two-parametric space, with voltage (V) and emission (β) as parameters. A second portion with S-switching is revealed in the current–voltage characteristics.

Electronic Structure Calculations for Au-doped Ge and Si with a Possible High Thermoelectric Power

Molecular orbital calculations were performed to investigate electronic structures of gold-doped germanium and silicon with consideration about the possibility of achieving high thermoelectric power. Calculational results show that in the case of Ge, the top of valence states is higher and the bottom of conduction states is rather lower compared to those in the case of Si. For Ge doped with Au, the atomic orbitals of Au contribute to energy levels just below the conduction states and above the valence states for Ge. A similar electronic structure is seen for Si doped with Au. In amorphous semiconductors, where Ge and Si are in contact with each other and doped with Au, ambiguous energy levels are usually formed near the bottom of the conduction states and the top of the valence states. Then, charge carriers may be introduced in the Si and Ge regions and may possibly enter the Ge and precipitated Au regions with a high energy. In addition, the energy levels of the conduction and valence states are lifted and lowered, respectively, when the interatomic distance becomes shorter. Since the Seebeck coefficient for amorphous semiconductors is a function of electron energy and electric conductivity which depend on the electron energy, the enhanced carrier energy will enhance thermoelectric power.

Fast surface states activated by silver ions on a germanium-neutral electrolyte interface

The activation peculiarities and fast surface state (FSS) parameters, including the recombination centers (RC) caused by adsorption of silver ions on a germanium surface in contact with a neutral electrolyte and oriented along the three main cristallographic planes (111), (110), and (100), were investigated. It has been detected that the anisotropy of the FSS and RC parameters differs from that found earlier for a “pure” germanium surface or for gold-doped germanium under analogous conditions, but agrees with the anisotropy of the potential distribution on the Ge-electrolyte interface and is apparently governed thereby, exactly as in later cases. The surface state parameters are quite close in all cases. The singularities in the kinetics of surface state activation are associated with the higher migration capability of the silver ions under the effect of polarization. It is shown that successive adsorption of gold and silver ions does not result in the effect of neutralizing the RC which is observed on a “dry” germanium surface in such a situation.

Impact ionization of deep acceptor gold in germanium

We observed the dependence of conductivity on an applied high electric field in compensated gold-doped germanium between 77 and 300K. A slight decrease in conductivity, mainly due to the field-dependent carrier mobility, is followed by a relatively large increase in conductivity. The magnitude of this increase depends on the lattice temperature, being larger at low temperatures, and on the compensation ratio. The increase in conductivity is supposed to be due to impact ionization of the frozen-out neutral acceptor gold in the strong electric field. This interpretation is supported by the temperature dependence of the hole concentration in the gold-doped germanium.

Determination of gold in germanium by neutron-activation analysis

Gold was determined in gold-doped germanium by neutron-activation analysis. The irradiated samples were dissolved in aqua regia, in the presence of gold carrier. The matrix activity was eliminated by distillation, and gold precipitated in the residue with hydroquinone. The gold fraction was essentially radiochemically pure. For a neutron dose of 5 × 10 15n/ cm 2, a sensitivity of 1 ppM Au can be obtained, with a 2·4-g sample. The samples investigated contained from 24 to 36 ppM Au.

Double-injection negative differential resistance in compensated gold-doped germanium

physica status solidi (a)Volume 12, Issue 2 p. K81-K82 Short Note Double-injection negative differential resistance in compensated gold-doped germanium N. L. Vanvari, N. L. Vanvari Solid State Electronics Laboratory, Department of Electrical Engineering, University of Cincinnati, OhioSearch for more papers by this authorH. Thurman Henderson, H. Thurman Henderson Solid State Electronics Laboratory, Department of Electrical Engineering, University of Cincinnati, OhioSearch for more papers by this author N. L. Vanvari, N. L. Vanvari Solid State Electronics Laboratory, Department of Electrical Engineering, University of Cincinnati, OhioSearch for more papers by this authorH. Thurman Henderson, H. Thurman Henderson Solid State Electronics Laboratory, Department of Electrical Engineering, University of Cincinnati, OhioSearch for more papers by this author First published: 16 August 1972 https://doi.org/10.1002/pssa.2210120247Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume12, Issue216 August 1972Pages K81-K82 RelatedInformation

A Fast Response Thin Film Wattmeter for Measurements of CO2 Laser Power

A thin platinum film wattmeter for measurements of instantaneous power output from a pulsed CO2 laser is presented. Its design, operating characteristics, calibration, and use in the experimental investigation are described. The time response of this gauge is shorter than 1 μsec. The response of this gauge is linear for exposure duration of up to about 20 msec and up to total laser energy of about 100 J. The thin film wattmeter was used for measurements of the power output obtained in CO2 gasdynamic laser experiments in a shock tunnel. The laser radiation measurements of the thin film gauge are compared to those obtained with gold-doped germanium detector. The absolute power output values obtained from the calibrated thin film wattmeter are in agreement with theoretical calculations.

DIRECT OBSERVATION OF THE ASHLEY-MILNES THREE-HALVES POWER LAW POTENTIAL VERSUS DISTANCE IN THE PREBREAKDOWN SQUARE LAW REGION OF GOLD-DOPED GERMANIUM DOUBLE-INJECTION DIODES

Measurement of potential distributions versus distance in gold-doped germanium double-injection diodes have been made and compared to the Ashley-Milnes theory. Estimates of capture cross sections of the gold centers based on these measurements have been calculated to be σn0=10−16 cm2 and σn− = 3 × 10−17 cm2 at 77.2°K.

I.R. absorption corresponding to transitions of holes from impurity levels to the valence band in silicon and germanium

Absorption due to indirect transitions of holes from the boron levels to the valence band in silicon was recorded with the aid of penetrating exciting light. Two peaks for the absorption change produced by illumination were obtained which could be related to transitions from the two upper valence bands and from the lower valence band to the impurity level respectively. The participating phonon energies were determined and a value for the spin-orbit splitting in silicon was obtained. The measurements also made it possible to explain certain results from earlier measurements on borondoped and indium-doped silicon. The absorption increase recorded as a function of the exciting light intensity was in good agreement with a curve calculated theoretically for the assumed conditions. From the results obtained, the conclusion may be drawn that the time interval during which the bound holes preserve their k values is considerably larger than the lifetime of the holes. Finally, some measurements were made on intrinsic and gold-doped germanium and the spectral distribution of the absorption due to a gold level was determined.

Response of a Triglycine Sulphate Pyroelectric Detector to High Frequencies (300 kHz)

The theory and performance of two types of pyroelectric TGS detectors working at room temperature, one type having electrodes on the front and back surfaces of the crystal plate and the other type with electrodes on the two-side surfaces, have been investigated. They have the same signal-to-noise (S/N) ratio at high frequencies, but the second type detectors, when used with a high-bias resistor, give a higher signal if they have a long edge parallel to the pyroelectric axis. One TGS detector, modified to give a bandwidth of 100 kHz was compared to a gold-doped germanium detector using a CO2 laser as the source. The S/N ratio of the TGS detector is nearly ⅕ of the germanium detector. The type II detector has also been used to study a HCN laser pulse. The possibilities of pyroelectric detectors working at room temperature appears promising in spite of their intrinsic character of thermal detectors.

Wavelength Dependence of Laser-Beam Scintillation*

An experiment has been performed to confirm the proportionality between log-amplitude variance and the 7/6 power of wavenumber predicted by Tatarski for horizontal propagation from a spherical-wave transmitter to a point detector. The validity of this proportionality was tested for two wavelengths: 0.632 and 10.6 μ. Beams from a helium-neon and a CO2 laser were simultaneously transmitted over a folded 1.2-km horizontal path and were detected with a photomultiplier and a gold-doped germanium detector. The primary scintillation statistic, log-amplitude variance, was evaluated for each wavelength with a digital computer and the ratio of variances at 0.632 and 10.6 μ was found to be in close agreement with predictions. Power spectral density, autocorrelation, and cumulative probability density were also evaluated for each wavelength. Scintillation statistics at 10.6 μ were found to be log normal, as in the visible.

Noise and oscillations in gold-doped germanium photodiodes

Considerable noise effects in excess of shot noise and oscillations found in commercially available, gold-doped germanium photodiodes have been investigated. The noise and oscillation effects occur in the photocurrent of reversely biased diodes at temperatures below about 100°K. The dependence of the observed phenomena on external parameters, such as voltage, current, illumination level and temperature has been studied. The excess noise is attributed to a modulation of the voltage across the junction due to generation-recombination fluctuations of the large bulk-resistance. The voltage across the junction modulates the current through the device, since the differential resistance of the junction is not infinite. There is reasonable agreement between the experiments and a simple theoretical model. The oscillations, which are not directly connected with the excess noise, are believed to arise owing to the presence of the gold levels, and might be associated with the recombination instability described by Bonch-Bruevich and Kalashnikov. In order to arrive at more definite conclusions better defined structures should be investigated.

A Radiometer-Sonde for Observing Emission from Atmospheric Water Vapor

A balloon borne instrument is described which measures the downward flux of thermal radiation from atmospheric water vapor in the region of 6.3 micro. Use is made of a liquid-air-cooled gold-doped germanium detector together with a 40 cps vibrating vane chopper which operates at the same temperature as the detector. The responsivity of the detector increases with height, enabling measurements to be made over about four orders of magnitude. Signals, after amplification and synchronous rectification, are transmitted to the ground via an FM/FM telemetry system. Regular energy calibration is performed by reference to a local blackbody at a known temperature. The complete assembly weighs 2.5 kg and is flown on a conventional rubber balloon as part of a regular meteorological sounding. Twelve ascents have been made and measurements obtained up to 32 km. Results have been used to calculate stratospheric humidity profiles.

Gold-Doped Germanium as an Infrared High-Frequency Photodetector

Gold-Doped Germanium as an Infrared High-Frequency Photodetector

Infrared temperature measurement of the laminar wake of a hypersonic sphere

The temperature of the laminar wake of a 0.22-in.-diam nylon spherical projectile traveling at 13,000 fps in a ballistic range filled with 95% N2 and 5% CO2 has been measured by observing the infrared radiation from the CO2 with a gold-doped germanium infrared detector and a 4.39-/X narrow-band filter. The results are compared with theoretical wake temperatures calculated by a two-step procedure. First, the cooling of the shock-heated gas as it expanded to ambient pressure was calculated by a streamtube chemistry program (developed by Lin and Teare). Subsequently, a simple heat conduction calculation was carried out. In the region from 50 to 400 body diameters behind the sphere the experimental CO2 vibrational temperatures (determined by fitting the radiation measurements with gaussian temperature profiles) agree with the calculated translational temperatures within the scatter of the data. For example, at 200 body diameters the measurements give 1230°K on the centerline while the theoretical temperature is 1410°K. Nearer the body the experimental values are as much as 600°K higher than calculated; a possible explanation for the discrepancy is discussed in the text.

Theory of Optical Beating in Photoconductors (Phenomenological Modification of Semiclassical Treatment)

Recent laser experiments have shown that two coherent light waves of slightly different frequency, when simultaneously incident on a photodetector, produce a photosignal modulated at the beat frequency $\ensuremath{\Delta}f$. The theory of this photomixing process is developed by means of a modification of the usual semiclassical treatment of radiation. This modification takes into account the finite lifetime $\ensuremath{\tau}$ of excited electronic states in the quantum-mechanical equations of motion. The photosignal is found to be proportional to ${[1+4{\ensuremath{\pi}}^{2}{\ensuremath{\tau}}^{2}{(\ensuremath{\Delta}f)}^{2}]}^{\ensuremath{-}\frac{1}{2}}$. This result suggests an experimental means of determining the lifetime by measuring the frequency response of the photosignal to the beat frequency. The theory compares favorably with experiments on $p$-type extrinsic gold-doped germanium.

Generation-recombination noise in various photoconductive semiconductors

Noise measurements are reported for nickel-doped germanium, manganese-doped germanium, gold-doped germanium, indium antimonide and tellurium. For nickel-doped germanium the noise spectra are found to be consistent with the g- r noise theory for double acceptor systems. The various capture cross-sections have been determined. At low temperatures the upper nickel level acts as a recombination center (hole trap). The noise spectra for manganese-doped germanium are complex at temperatures close to 77°K. The noise is extremely low and consequently a large detectivity as a radiation detector is to be expected. For gold-doped germanium, spectra were observed which are not of the usual form for multi-step relaxation processes. An explanation is suggested by noticing that the dielectric relaxation time for these samples is larger than the lifetime so that space charge transients can exist. Some noise data are given for indium antimonide together with an estimate for the noise equivalent power. Finally some features of noise in tellurium single crystals are reported.