Ge Single Crystals Research Articles

Double-hump diffusion profiles of copper and nickel in germanium wafers yielding vacancy-related information

Diffusion of Cu and Ni into Ge was investigated between 700 and 900 °C with the aid of rapid isothermal lamp annealing and spreading-resistance profiling. Using low-dislocation-density single-crystal Ge wafers with a backside gold layer, we observed typical double-hump diffusion profiles of both Cu and Ni. These profiles can be described within the dissociative model by taking into account that the front surface acts as source for both vacancies (V) and Cu or Ni while the back surface combines the V-source feature with a Cu, Ni-sink property. Profile fitting yields data regarding the V-assisted Ge self-diffusion coefficient and the equilibrium concentration of vacancies as a function of temperature.

Codoping of Ge with Al and Sb

Ge single crystals were doped with Al or Sb to various concentrations and codoped with Al and Sb in the ratios 3:1, 1:1, and 1 : 3. Using Hall effect measurements, the electron and hole concentrations in the doped crystals were determined. A relationship between the dopant-solubility limits and the maximum carrier concentration was found. The data obtained were shown to be consistent with the processes Al ↔ Al- + h and Sb ↔ Sb+ + e in Ge doped with Al or Sb up to the solubility limit. In the material codoped with Al and Sb in the atomic ratio 3 : 1, the hole concentration is equal to the difference in the Al and Sb concentrations. At an Al : Sb ratio of 1 : 3, the electron concentration in Ge(Al, Sb) is higher than that in Ge because of the increase in Sb solubility in the presence of Al. The crystals doped with equal concentrations of Al and Sb aren-type. The results are interpreted in terms of donor-acceptor interaction and compensation effect.

Effects of Mechanical Constraint on the Strength of Ni<SUB>3</SUB>Ge Single Crystals

Dislocation structures in Ni 3 Ge single crystals have been studied after deformation by [001] compression. In these tests octahedral slips govern the plastic deformation in absence of resolved stress for cube slips, causing anomalous strengthening throughout the temperature range studied, 77500 K. Restriction of the operative shear systems by application of mechanical constraint is shown to increase the work hardening rate for the [001] compression. This phenomenon is opposite to the decrease of work hardening rate by the imposed constraint found for pure Cu in similar experiments. Three-dimensional dislocation structure has been examined by a high voltage electron microscope. Based on these observations, origin of the rapid work hardening and the anomalous strengthening in Ni 3 Ge is attributed to a fine and non-planner dislocation structure developed in absence of resolved shear stress for the cube slips.

Anomalous effects in dopant distribution in Ge single crystals grown by the floating zone technique aboard spacecrafts

Specific features of Ga-dopant distribution in Ge single crystals grown by the floating zone technique from lightly and heavily Ga-doped Ge melts aboard the Photon spacecrafts have been studied. An anomalously strong concentration dependence of the effective coefficient of Ga distribution in Ge crystallized from melts with a well-developed free surface, which has no analogues under the terrestrial conditions, has been established for the first time. This anomaly is interpreted as a consequence of specific concentration-dependent processes of heat and mass transfer in the molten zone, and, first of all, the intensification of the concentration-capillary convection with an increase of the doping level. The quantitative characteristics of the crystallization parameters necessary for the construction and verification of hydrodynamic models are obtained experimentally. The effect of the observed phenomena on the electrophysical homogeneity of the grown single crystals and possible methods for the control of dopant distribution in such crystals are discussed.

Anomalous effects of dopant distribution in Ge single crystals grown by FZ-technique aboard spacecrafts

The gallium distribution in nine germanium single crystals, all grown with similar heat conditions using the floating zone (FZ) method aboard five unmanned “Photon” spacecrafts (SC), from melts doped from 1×10 18 to 1×10 20 at/cm 3 are studied. For the first time, the strong anomalous concentration dependence of the distribution coefficient (from 0.16 to 0.089, respectively), having no “earth” analogue, was revealed experimentally as a result of comparative studies of space-grown and reference crystals. It also was shown, that the revealed dependence can completely define the longitudinal dopant distribution profile in a single crystal. The hypothesis of the nature of the observed effect was proposed, which consists of an intensification of the mixing processes in the heavily doped molten zone, restricted by free surface, caused by an increase of the surface-active impurity content in reduced gravity.

73Ge NMR spectra in germanium single crystals with different isotopic composition

We have studied the influence of isotopic disorder on the local deformations in Ge single crystals from both experimental and calculation points of view. The nuclear magnetic resonance (NMR) spectra of73Ge nuclei (the nuclear spin equals 9/2) in perfect single crystals of germanium with different isotopic content were measured at temperatures 80, 300 and 450 K. Abnormal broadening of the spectrum was found to occur when the magnetic field was aligned along the [111] axis of a crystal. The observed specific angular dependence of the quadrupole broadening was attributed to isotopic disorder among atoms of germanium sited around the73Ge NMR probe. Local lattice deformations in germanium crystal lattice due to isotopic impurity atoms were calculated in the framework of the adiabatic bond charge model. The results obtained were applied to study random noncubic crystal field interactions with the nuclear quadrupole moments and corresponding effects in NMR spectra. Simulated second and fourth moments of resonance frequency distributions caused by the magnetic dipole-dipole and electric quadrupole interactions are used to analyze the lineshapes, theoretical predictions agree qualitatively with the experimental data.

Back-Scattered Electron Imaging of Microscopic Segregation in (Si,Ge) Single Crystals

Compositional inhomogeneities of (Si,Ge) single crystals grown by the radio frequency (RF) heated float zone technique have been studied using the back-scattered electron (BSE) mode of a scanning electron microscope. Numerical analysis of the images by Fast Fourier Transformation (FFT) showed that the number of spatial frequencies with substantial amplitudes is increased when investigating longitudinal sections of crystals containing dislocations instead of dislocation-free crystals. This can be attributed to different growth conditions in terms of super-cooling.

Positioning of self-assembled, single-crystal, germanium islands by silicon nanoimprinting

Strain energy from the lattice mismatch of a heteroepitaxial system can create “self-assembled,” single-crystal islands irregularly arranged on the surface. Alternatively, features of tens of nanometers can be patterned on a substrate by “nanoimprinting” using a mold and etching. When these two techniques are combined, the small patterned features can interact with the self-assembly process, causing the islands to form at the patterned features. The resulting regular array of very small islands may be useful for future devices. The positioning of single-crystal Ge islands by Si mesas formed by nanoimprinting and etching is demonstrated in this letter.

Optical and magnetooptical study of photorefractive germanium-doped cadmium telluride

A photorefractive CdTe:Ge single crystal was investigated via photo-absorption at room temperature, 98 K and 4.3 K, and magnetic circular dichroism at 1.4 K. At all wavelengths, except near 1064 nm, absorption spectra suffer relatively large changes under various illuminations. Magnetic circular dichroism demonstrates unambiguously the presence of two paramagnetic defects, one of them being the ionised donor Ge + at the Cd site. Our results further reveal the existence of four absorption components around 0.94 eV, 1.10 eV, 1.22 eV and 1.36 eV. The two extreme ones are assigned to the photoneutralisation of Ge Cd + and to the photoionisation of Ge Cd 0 respectively.

Mechanisms of energy dissipation during displacement- sensitive indentation in Ge single crystals at elevated temperatures

Abstract Load-displacement indentation tests have been performed in Ge single crystals on a newly designed displacement-sensitive hardness tester in the temperature range 20–450°C. The deformation substructure in the vicinity of the indentation impressions was investigated using selective etching. The energy dissipated during the loading-unloading indentation cycle has been measured and compared with the extent and the structure of the deformation zone. Mechanisms of plastic flow and fracture during indentation are discussed.

Mechanisms of energy dissipation during displacementsensitive indentation in Ge single crystals at elevated

Abstract Load-displacement indentation tests have been performed in Ge single crystals on a newly designed displacement-sensitive hardness tester in the temperature range 20–450°C. The deformation substructure in the vicinity of the indentation impressions was investigated using selective etching. The energy dissipated during the loading-unloading indentation cycle has been measured and compared with the extent and the structure of the deformation zone. Mechanisms of plastic flow and fracture during indentation are discussed.

Tem Observations of Interfacial Defects in Mocvd GaAs on Single Crystal Ge Substrates

Abstract The growth of high quality GaAs layers on single crystal Ge substrates has attracted a great deal of interest in recent years. Currently under development at NREL is the GaAs/GalnP-on-Ge high efficiency multi-junction solar cell. Unlike other heteroepitaxial systems such as GaAs-on-Si, physical properties such as the lattice parameter and thermal expansion coefficient of the Ge and GaAs are much closer. Further, Ge has a bandgap of 0.7 eV that makes it a suitable bottom cell in a multi-junction stack. However, the growth of GaAs on Ge is not a straightforward process, and little is known about the Ge surface and the nucleation of GaAs on Ge in the MOCVD environment. In this study, TEM results show that a number microstructural defects are associated with the Ge/GaAs interface and the initial stages of growth.

Graded X-ray Optics for Synchrotron Radiation Applications.

Using X-ray diffractometry and spectral measurements, the structure and properties of graded X-ray optical elements have been examined. Experimental and theoretical data on X-ray supermirrors, which were prepared by the magnetron sputtering technique using precise thickness control, are reported. Measurements on graded aperiodic Si(1-x)Ge(x) single crystals, which were grown by the Czochralski technique, are also presented. The lattice parameter of such a crystal changes almost linearly with increasing Ge concentration. The measurements indicate that Si(1-x)Ge(x) crystals with concentrations up to 7 at.% Ge can be grown with a quality comparable to that of pure Si crystals.

FTIR internal reflection spectroscopy studies of the effect of pH on adsorption of oleate/oleic acid at the surface of a TiO 2 thin film deposited on a Ge single crystal

The adsorption of oleate/oleic acid from aqueous solutions at the surface of titanium dioxide was examined by Fourier transform infrared (FT-IR) spectroscopy using a germanium internal reflection element coated with a thin film of TiO 2. This thin film, with a thickness of 100–200 Å, was deposited on the surface of a germanium single crystal by rf dc magnetron reactive sputtering. It was found that significant adsorption of oleate/oleic acid from a 0.03 mM aqueous solution occurs at neutral and close-to-neutral pH, from about pH = 4.5 to pH = 8.5. The surface density vs. pH relationship obtained in this study is consistent with literature reports on the effect of pH on flotation recovery of rutile from oleic acid solutions.

Mechanical Strength and Dislocation Velocities in GeSi Alloys

The mechanical strength and dislocation velocities in single crystal Ge 1-x Si x alloys grown by the Czochralski method were investigated by compressive deformation and by the etch pit technique, respectively. In the temperature range 450-700°C and the stress range 3-20 MPa, the dislocation velocity in the GeSi with x = 0.004-0.022 decreases monotonically with an increase in the Si content, reaching about a half of that in Ge at x = 0.022, and can be expressed as a function of the stress and the temperature as expressed by the empirical equation known in other semiconductors. The yield stress of the GeSi alloy increases with increasing Si content from x = 0 to 0.4 and is temperature-insensitive at high temperatures, showing that the flow stress of alloy semiconductor has an athermal component which is absent in elemental or compound semiconductors. The hardening mechanism in alloy semiconductors is discussed.

Isotropy of ion-induced electron emission from crystal targets bombarded with MeV ions

We have experimentally studied emission-angle dependence of the keV electron yield from Si and Ge single crystals bombarded with MeV H+ and He+. The observed electron yield showed no discernible dependence on the crystallographic direction of the outgoing path of the electrons. It is concluded that the dominant effect of the crystal lattice on the ion-induced electron emission is the ion-beam shadowing effect associated only with the production process of the electrons.

Euroball: Present status and outlook

Euroball is a European project to build a highly efficient and powerful gamma-ray spectrometer for nuclear structure spectroscopy. The project is an amalgamation of recent technical advances in detectors, electronics and data acquisition. In the first phase the spectrometer consists of 30 large single crystal Ge detectors, 26 Clover Ge detectors and 15 Cluster Ge detectors each with an associated suppression shield. The 239 individual Ge detector elements will have a total photopeak efficiency ∈p of ≈ 10% and will enable the properties of the atomic nucleus to be studied with a sensitivity up to or better than 10−5 of the production cross-section. The elements of the spectrometer, including the detectors, the electronics and the data acquisition system, some of the planned ancillary detectors and the first results will be presented. Several developments are under investigation for the upgrade of Euroball for its second phase. These include an inner BGO ball for multiplicity and summed energy determination and inner particle detectors for charged particle identification. These developments will also be discussed.

Electrical properties of evaporated polycrystalline Ge thin-films

Electrical properties of Ge thin films evaporated on Si 3N 4 CVD-coated Si substrate were improved by introducing a heat treatment after the deposition of Ge films. Evaporation conditions were optimized by changing the substrate temperature and deposition rate, and then, heat treatment was performed. At substrate temperatures during the evaporation lower than 300 °C and higher than 400 °C, deposited films were amorphous and polycrystalline, respectively. At substrate temperatures lower than 400 °C, Ge films were evaporated without degrading the surface roughness. The Hall mobility of films evaporated at room temperature increased with increasing the substrate and heating temperature and showed about 400 cm 2 V −1 s −1 for the hole concentration of 4 × 10 17 cm −3 at the heating temperature of 900 °C. This value was almost comparable to that of p-type Ge single crystal.

Anomalous Dislocation Kink Drift in Germanium

The evolution of kink pairs on dislocations in Ge single crystals under two-level intermittent loading has been studied in order to reveal modes of one-dimensional transport in a random environment. Experimental evidence has been obtained for the anomalous nonlinear kink drift predicted earlier by theory.

X-Ray Dispersion Corrections Obtained by Rocking Curve Measurements for Ge and GaAs Single Crystals

The real and imaginary parts of the X-ray dispersion correction, f ′ and f ′′ , for Ge, Ga and As near the K-absorption edges are obtained by rocking curve measurements for a Ge and a GaAs single crystal. The experiments are carried out using synchrotron radiation at the KEK Photon Factory. The energy dependencies of f ′ and f ′′ show the fine structures above the absorption edge. Except for the fine structures the experimental results are in good agreement with the theoretical values for Ge but there are systematic differences between experimental and theoretical values for Ga and As.