Germanium Crystals Research Articles

Annealing restoration of HPGe detector

HPGe detector is used widely, its property is affected by neutron. Annealing to the germanium crystal is a good approach to recover the detector. To raise the temperature of germanium crystal to recover the resolution for the HPGe detector. A special copper ingot is designed and manufactured to increase the heating efficiency. Two temperature controlled power supplies are used to heat the germanium crystal and keep the temperature for cooling rod. The experiment results indicate that raising temperature to 70 $${}^\circ \hbox {C}$$ for five days, the restoration efficiency is better than 90%.

Crystallization of Ge in ion-irradiated amorphous-Ge/Au thin films

Herein, the structural, optical, and electrical properties of Au-induced crystallization in amorphous germanium (a-Ge) thin films are presented for future solar energy material applications.

Фемтосекундный лазерный отжиг многослойных тонкопленочных структур на основе аморфных германия и кремния

Femtosecond laser annealing of thin-film multilayered structures based on amorphous silicon and germanium were studied. The original samples were synthesized via plasma-enhanced deposition on glass substrate. Scanning electron microscopy revealed formation of periodic surface structures in the irradiated films. Raman spectra analysis revealed crystallization of amorphous germanium as a result of femtosecond laser pulses action, as well as fluence-dependent mixture of the germanium and silicon layers at absence of crystallization of the amorphous silicon layers.

Optical and structural properties of ZnS0.5Se0.5 films and interference filters based on them

In this study, the structural and optical properties of thin films of a ${{\rm ZnS}_{0.5}}{{\rm Se}_{0.5}}$ZnS0.5Se0.5 solid solution, which are used to create multilayer interference coatings for operation in the near- and mid-infrared regions, are investigated. The structural features and phase composition of the initial film-forming material and films obtained by thermal evaporation in a vacuum on substrates of borosilicate glass and single crystals of germanium and silicon are studied by X-ray diffraction analysis. The dispersion dependences of the optical constants are calculated from spectrophotometric measurements of the films studied here in the spectral range of 2–25 µm. The results of designing and manufacturing infrared interference filters using the films studied here are presented, which include a bandpass filter with transmission in the wavelength range of 8–12 µm and a narrow-bandpass filter with maximum transmission at a wavelength of 10.56 µm and a full width at half-maximum of 140 nm.

Cosmogenic Activation of Germanium Detectors in EDELWEISS III

Activation of germanium crystals due to cosmic rays becomes a serious limitation for experiments searching for rare events with germanium detectors. Cosmic ray induced activation of the detector components and, even more importantly, of the germanium itself during production, transportation and storage at the Earth’s surface, might result in the production of radioactive isotopes with long half-lives, with a possible impact on the expected background. We present a measurement of the cosmogenic activation in the cryogenic germanium detectors of the EDELWEISS III direct dark matter search experiment. The decay rates measured in detectors with different exposures to cosmic rays above ground are converted into production rates of different isotopes. They are compared to model predictions present in literature and to estimates calculated with the ACTIVIA code.

Fluent simulation and experimental analysis of polished surface topography of single crystal germanium

Single crystal germanium has good physical and chemical properties but it is hard to be processed. Some researchers thought the flowing effort has no effect on the removal of test-piece surface material during the polishing process. This paper had built a flow-path simulation model and used Fluent to simulate the polishing process and designed experiment to analyse the polishing process. It was found in experimental results that, during the polishing process two-phase flow could smooth the surface of single crystal germanium, but it could also cause the edge surface material uneven removal on the test-piece, moreover, the uneven degree on both sides of polished test-piece were different, the roughness on middle part of test-piece was smaller than edge sides. Meanwhile, the residual stress was mainly caused by abrasive material properties and other conditions. The conclusion mentioned above were consisted with the simulation results, which proved the correctness of simulation model and assumptions, and the flowing effect of polishing liquid had effect on the removal of surface material. The paper provides a new research thought on two phrase flow polishing.

A novel multiscale approach to brittle fracture of nano/micro‐sized components

AbstractPrinciples and advantages of a new concept based on the ab initio aided strain gradient elasticity theory are shown in comparison with the classical Barenblatt cohesive model. The method is applied to the theoretical prediction of the critical energy release rate and the crack tip opening displacement at the crack instability in nanopanels made of germanium and molybdenum crystals. The necessary length scale parameter l1 is determined for germanium and molybdenum by the best gradient elasticity fits of ab initio computed screw dislocation displacements and phonon dispersions. Values of ab initio computed critical energy release rates and crack opening profiles revealed that the length l1 is related to inflexion points of profiles. A novel ab initio method in combination with continuum mechanics was successfully tested to replace molecular statics dependent of availability of interatomic potentials. The asymptotic strain gradient elasticity solution for displacement components near the crack tip in materials with cubic lattice was also derived.

Spectral dependencies of terahertz emission from femtosecond laser excited surfaces of germanium crystals

Pulsed terahertz emission excitation spectra from germanium crystals are being presented. The most intense terahertz pulses from germanium crystals are emitted at quanta energies coinciding with technologically significant telecommunication wavelengths. The terahertz generation mechanisms are an interplay of the photocurrent surge in the surface electric field and the photo-Dember effect. Remarkably, the terahertz emission is also observed at quanta energies below the direct bandgap of this material even when photoexcited at a surface normal. This is the result of a broken symmetry of effective electron mass in the L valleys.

Technology development of high purity germanium crystals for radiation detectors

Abstract High Purity Germanium (HPGe) crystals are indispensable for radiation detection and fundamental research. Among other applications they will be used in the Large Enriched Germanium Experiment for Neutrinoless double beta Decay (LEGEND) experiment for the search of neutrinoless double beta decay of 76 Ge. Ongoing research activities are done in collaboration with members of the existing GERDA experiment. In this context the Leibniz-Institut fur Kristallzuchtung (IKZ) is engaged in the development of HPGe Czochralski crystal growth including purification and characterization of the material. The Ge starting material is purified in a horizontal multi-zone furnace. Two inch Ge single crystals were grown by the Czochralski method and analyzed with respect to electrically active impurities by means of Hall-effect measurements and Photo-thermal Ionization Spectroscopy. The dislocation density is assessed by combining defect etching and optically microscopy imaging. Lateral Photovoltage Scanning is applied to visualize doping striations, which bear information on the shape of the solid–liquid phase boundary during growth.

Germanium-doped silicon (sige) as a material for the manufacture of power semiconductor devices resistant to secondary cosmic radiation

The problem of unpredictable failure of power semiconductor devices can be solved by using technologies that increase their radiation resistance. The use of single crystals of germanium doped silicon slows down the degradation of the characteristics of devices when exposed to ionizing radiation, which is an alternative to scarce and expensive GaAs, GaN, SiC, used for these purposes. The impact of secondary cosmic radiation may be responsible for the degradation of the electrophysical parameters of silicon single crystals during their long-term storage, as well as for the decrease in the operating efficiency of semiconductor solar energy converters.

Thermal stability of the properties of germanium crystals for IR optics

Both Sb-doped Germanium and Ge-Si solid solution single crystals with resistivity from 1.5 to 7 Ω·cm were grown using the Czochralski method. The optical transmission of single crystals and the stability of their optical properties were studied by infrared Fourier spectroscopy at a wavelength of 10.6 μm and temperature range from 25 to 60 °C. It was found that decreasing the background impurities concentration leads to the reduction of the infrared absorption at room temperature while not affecting the thermal stability of the optical properties. Thermal stability of the optical properties of Sb-doped germanium single crystals increases by adding from 0.2 to 0.8 at % of silicon.

Effect of rotation on impurity distribution in crystal growth by Bridgman method

This work is devoted to the numerical (FE) study of the influence of crucible and submerged heater rotation on the distribution of doping gallium in germanium crystals grown by Bridgman method with submerged heater. The influence of crucible and submerged heater rotation on the impurity distribution in the melt and in the crystal for constant and oscillating rotation speeds is shown for the earth conditions and weightlessness conditions.

Modeling an HPGe detector response to gamma-rays using MCNP5 code

The response function is the important information for the precise interpretation of experimental data and also for characterizing the developing nuclear instruments. Measurement of the response function normally requires a number of mono-energetic gamma-ray sources, a long acquisition time and an appropriate experimental setup. The Monte Carlo method, as an alternative to response function measurement, has widely been used and recommended. In this study, a computational model of an HPGe detector has been developed by using the MCNP5 code. To validate the simulated model, the simulations from mono-energetic sources have been compared to the corresponding measured data. Any deviation from the measurement could be attributed to the unmodeled details of the detector crystal, so they needed adjustment. Moreover, an analysis has been undertaken on the dependency of detection efficiency on the dead layer thickness of the germanium crystal. Having developed a computational model of the crystal, a set of correction factors was extracted to take into account the gamma-ray self-absorption within the source volume. The simulated model of the HPGe detector in this study can be used to calculate the detection efficiency when the samples are not of the standard geometry which require self-absorption considerations.

Fluent simulation and experimental analysis of polishing edge abrasion of single crystal germanium

Single crystal germanium has good physical property and is widely used, but it is hard to process the surface of single crystal germanium by traditional processing technology. Although using two-phrase flow polishing technology can make effective processing on the surface of single crystal germanium, but it could also cause edge abrasion as well. The paper was based on two-phrase flow polishing theory, which built a flow-path simulation model based on the location relationship of each part of polishing machine, used Fluent to simulate the polishing process and designed experiment to analyse the polishing process. By simulation and experimental analysis we can find that, during the polishing process, the liquid-solid two-phrase flow would cause edge abrasion of test-piece, but the abrasion degree on each side of the test-piece is different. The difference of pressure which caused by liquid flow and the change of flow-path size are the main reasons of edge abrasion. Under existing processing conditions, using diamond abrasive could get higher surface accuracy, but the edge abrasion of the specimen is obvious. To reduce the edge abrasion, larger size of abrasive should be used.

Micro ATR-FTIR spectroscopic imaging of colon biopsies with a large area Ge crystal.

A new large-area germanium ATR crystal is utilised with an FTIR microscope to improve the acquired images of de-paraffinized colon biopsy sections, without recourse to a synchrotron source. The large crystal (⌀ = 28 mm) offers significant improvements compared to slide-on small germanium crystal (⌀ = 3.5 mm); for example, it facilitates more uniform distribution of higher signal intensity within the field of view and more rapid acquisition time. Mapping of a larger sample area up to ca. 350 × 350 μm2 with this new set-up, coupled with imaging using an FPA detector, is demonstrated for the first time on biological specimens. The performance of k-means clustering algorithm applied to classify the different anatomical structures of the colon biopsies is greatly improved with mapping. Comparison of H&E stained adjacent tissue sections with false-colour k-means images strongly support differentiation of five distinct regions within tissues. The efficiency of the methodology to categorise colon tissues at various stages of malignancy is analysed via multivariate chemometrics. The second derivative spectra extracted from the crypt region of the colon were subjected to Partial Least Squares classification. Good separation between data in clusters occurs when projecting spectra on a PLS score plot on a plane made by the first 3 principal components. Important spectral biomarkers for colon malignancy classification were identified to exist mostly in the fingerprint region of the FTIR spectrum based on the chemometrics analysis.

Single crystal HPGe (80%) versus BGO shielded CLOVER detector for high precision decay rate measurements: a comparative study

In this study, various detector configurations have been investigated in order to explore the optimal condition for decay rate measurements of radioactive samples using gamma spectroscopy technique. A limitation of detecting low energy gamma rays from decaying radioactive nuclei, is the Compton background which can be significantly reduced by rejecting Compton scattered events through active Bismuth germanate (BGO) shielding. On the other hand, for a CLOVER detector without BGO shielding, one can place the radioactive samples very close to the detector for enhancing geometrical efficiency. A single crystal High Purity Germanium (HPGe) detector can also be used for decay rate measurements. In order to measure the decay rate of nuclei decaying via gamma emission with reasonable intensity, optimal close geometry options have been investigated for various HPGe detector configurations.

Refractive index spectral dependence, Raman spectra, and transmission spectra of high-purity 72Ge, 73Ge, 74Ge, 76Ge, and natGe single crystals.

The results of the precise measurement of the refractive index of stable germanium isotopes Ge72, Ge73, Ge74, and Ge76 single crystals with high enrichment and a germanium single-crystal Genat of natural isotopic composition with the Fourier-transform interference refractometry method from 1.94 to 20μm with 0.1 cm-1 resolution and accuracy of 2×10-5 to 1×10-4 are shown. The content of 72 impurities measured by the mass spectrometric method was below 10-5-10-6 wt. %. Oxygen and carbon concentrations measured by IR spectroscopy in all crystals are within 5×1015 cm-3. All germanium crystals have a hole conductivity with specific electric resistivity of 45-50 Ohm×cm. The coefficients of the generalized Cauchy dispersion function approximating the experimental refractive index values all over the measuring range are given. The transmission and Raman spectra are also given.

Ambipolar transistor action of germanane electric double layer transistor

Germanane (GeH) is a hydrogen-terminated layered crystal of germanium. We fabricated an electric double layer transistor (EDLT) on a GeH thin film on the Ge (111) substrate and investigated its electronic properties. The EDLT showed ambipolar transfer characteristics at 240 K. The sheet resistance Rsheet at null gate bias (VG = 0 V) exceeded 1 MΩ below 100 K, which indicates an insulating behavior. For VG = −2 V (hole accumulation), a gradual increase in Rsheet up to 10 kΩ was found upon decreasing temperature to 40 K, i.e., semiconducting or even weakly insulating. Remarkably, Rsheet for VG = 1 V (electron accumulation) decreased down to 3 kΩ upon decreasing temperature to 40 K, indicating metallic conduction. Accumulation of electrons (holes) was confirmed for VG > 1 V (VG < −1 V) by Hall effect measurements. Hall mobilities of electrons and holes, which increase with decreasing temperature, were 6500 cm2 V−1 s−1 and 570 cm2 V−1 s−1, respectively, at 120 K.

Impurity concentration dependent electrical conduction in germanium crystals at low temperatures

A germanium single crystal of 7 N+ purity with a diameter of 45 mm and a length of 100 mm has been grown by the Czochralski method. The structural quality of the crystal has been characterized by Laue diffraction. Electrical conduction and Hall measurements are carried out on samples retrieved from different parts of the crystal along the growth axis. The top part of the crystal exhibits the lowest impurity concentration ($${\sim } 10^{12}\,\hbox {cm}^{-3})$$ that gradually increases towards the bottom ($$10^{13}\,\hbox {cm}^{-3})$$. The crystal is n-type at room temperature and the resistivity shows a non-monotonic temperature dependence. There is a transition from n-type to p-type conductivity below room temperature at which bulk resistivity shows a maximum and dip in carrier mobility. The intrinsic to extrinsic transition region shifts towards room temperature as the impurity concentration increases and it reflects the purity level of the crystal. A similar trend is observed in the boron-implanted high purity germanium (HPGe) crystal at different doping levels. The phenomena can be understood as a result of interplay between a temperature dependent conduction mechanism driven by an impurity band and an intrinsic carrier in Ge crystals having fairly low acceptor concentrations ($${<}10^{12}\,\hbox {cm}^{-3})$$.

(Invited) Sputter Beam Epitaxy for Atomic Ordering in Complex Epitaxial Thin Films

Innovation is driven by the materials mankind has mastered to advance society. Our information age traces back to wartime invention of methods to fabricate silicon and germanium crystals with defects lower than 1 part in 100, a threshold at which the intrinsic properties could then be applied. Today, complex materials (>2 elements with atomic ordering) are at a similar inflection point. Unfortunately, improvement beyond 1 defect in 4 has proven challenging: energetic defects abound and many elements are not compatible with current low-defect growth techniques. Despite significant external funding for the materials themselves, a lack of funding for new synthetic technologies has left us with methods unable to reach the inflection point. Our goal is to transform materials discovery by developing a complex material thin film system that can attain 99% atomic ordering in today’s “too-complex” materials. This talk will highlight our progress in thin film growth via Sputter Beam Epitaxy, an approach combining the fabrication strengths of off-axis magnetron sputtering and molecular beam epitaxy.