Ge Single Crystals Research Articles

Optical Properties of Single-Crystal Germanium in the THz Range

The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the attenuation coefficient of intrinsic germanium in the range of 160‒220 μm is at a level of ~0.5 cm‒1, a value comparable with that for silicon. The free-carrier absorption cross sections of silicon and germanium are significantly different, which may be caused by the difference in the mechanisms of carrier–phonon interaction in these materials.

The impact of intrinsic conductivity on the mechanisms of tensoresistance of uniaxially deformed n-Ge single crystals

The impact of intrinsic conductivity on the mechanisms of tensoresistance of uniaxially deformed <i>n</i>-Ge single crystals

Полупроводниковые плазменные антенны, формируемые лазерным излучением

The efficiency of transmission of high-frequency signals by a semiconductor-transmitting antenna made of Ge and Si single crystals on the surface of which a nonequilibrium electron-hole plasma is formed by laser diode radiation is experimentally investigated. The dependences of the amplitude of the emitted microwave signal in the range of 6 - 7.5 GHz on the laser power and the size of the irradiated area on the semiconductor transmitting vibratory antenna are obtained. It is shown that the efficiency of the useful signal transmission when forming a plasma antenna in Ge crystals can be increased by more than an order of magnitude.

Оптические свойства монокристаллического германия в терагерцовой области спектра

AbstractThe transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the attenuation coefficient of intrinsic germanium in the range of 160‒220 μm is at a level of ~0.5 cm^‒1, a value comparable with that for silicon. The free-carrier absorption cross sections of silicon and germanium are significantly different, which may be caused by the difference in the mechanisms of carrier–phonon interaction in these materials.

Effect of Crystallization Front Shape on the Dislocation Density in Germanium Single Crystals

The effect of crystallization front shape on the dislocation density in Ge single crystals with a diameter of 100 mm, grown by the Czochralski method, has been studied. The dislocation density in crystals with a convex crystallization front is found to be considerably higher. The average dislocation density in experimental ingots with deviation of crystallization front shape from flat in the range from –1.5 to +1.5 mm increases from 75 to 1000 cm–2 and from 75 to 700 cm–2 in the cases of convex and concave fronts, respectively. Minimum dislocation densities are observed for a flat or slightly concave front.

Physical properties of quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals

We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural feature of these materials is the anti-CaF2-type CoAl4T2 slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for Gd2CoAl4Ge2 and Gd2CoAl4Si2, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd3+ ions.

Interface characteristics of different bonded structures fabricated by low-temperature a-Ge wafer bonding and the application of wafer-bonded Ge/Si photoelectric device

We report the interface characteristics of Si/Si, Si/SiO2, SiO2/SiO2, Ge/Si, Ge/Ge, and Ge/SiO2 bonded wafers based on an amorphous germanium (a-Ge) intermediate layer. The crystallization of a-Ge and the atom migration mechanism at different bonded structures are very different. The a-Ge turns into polycrystalline Ge (poly-Ge) at Si/Si bonded interface, while it exhibits amorphous phase at Si/SiO2 and SiO2/SiO2 interfaces after post-annealing. This is due to the change of the stress field when SiO2 is introduced. Thanks to the crystallization of a-Ge, serious atom migration appears at Si/Si bonded interface, leading to the decomposition of the interface oxide layer formed by the hydrophilic reaction. Interestingly, the a-Ge at Ge/Si, Ge/Ge, and Ge/SiO2 interface becomes single-crystal Ge after post-annealing. The a-Ge crystallization starts from a-Ge/Ge interface. Similarly, the interface Ge oxide layer also decomposes after the crystallization of a-Ge. This results from the atom redistribution triggered by Ge-induced crystallization under high thermal stress. More importantly, the threading dislocations are not observed at Ge/Si and Ge/SiO2 interface. The Si/Si, Si/SiO2, SiO2/SiO2, and Ge/SiO2 bonded interface is demonstrated to be bubble-free. The transferring of the interface by-products (H2O and H2) by SiO2 and poly-Ge can be responsible for this phenomenon. Finally, a wafer-bonded Ge/Si heterojunction photodiode is fabricated to verify the application of a-Ge wafer bonding technique in photoelectric devices.

Investigation of Electromagnetic Interference Shielding Effectiveness of CZ Grown Ge Optical Windows

AbstractIn this study, different Ge IR optical windows are produced and their electromagnetic interference (EMI) shielding performances are investigated. Three Ge single crystals with different doping concentrations are grown by the Czochralski (CZ) technique. Optical windows are obtained after the slicing, lapping, and polishing processes are examined. Formation of (111)‐oriented single crystal is observed from the X‐ray diffraction (XRD) pattern. In addition, IR transmission of the crystals is measured around 45% in the range of 2–12 µm using Fourier transform infrared spectrometer (FTIR) spectrometer. EMI shielding effectiveness (SE) of the windows is determined in a flanged coaxial SE tester developed for outer diameter as 1 inch. SE results are evaluated by taking into account both resistivity, thickness of the samples and limitations of measurement fixture.

Interface characteristics and electrical transport of Ge/Si heterojunction fabricated by low-temperature wafer bonding

We report a promising method for oxide-layer-free germanium (Ge)/silicon (Si) wafer bonding based on an amorphous Ge (a-Ge) intermediate layer between Si and Ge wafers. The effect of the exposure time (te), during which the a-Ge is exposed to the air after sputtering and being taken out of the chamber on the bubble density at the bonded interface, is identified and a near-bubble-free Ge/Si bonded interface is achieved for the te of 3 s. The crystallization of a-Ge at Ge/Si bonded interface starts from a-Ge/Ge interface and it fully turns to be single-crystal Ge after post-annealing. The oxide layer at a-Ge/a-Ge bonded interface formed by the interface hydrophilic reaction disappears due to the atom redistribution triggered by the crystallization of a-Ge. As expected, the performance of the Ge/Si heterojunction diode is significantly improved by this oxide-layer-free Ge/Si bonded interface. A low dark current of 1.6 µA, high on/off current ratio of 3.4 × 105, and low ideality factor of 1.02 (150 K) is achieved at −0.5 V for the bonded Ge/Si diode. Finally, the carrier transport mechanisms at Ge/Si bonded interface annealed at different temperatures are also clearly clarified.

Two-Photon Absorption of Nonchain HF Laser Radiation in Germanium Single Crystals

Some results of experimental and numerical studies on the transmission of a nonchain high-frequency (HF) laser beam through germanium (Ge) single crystals of differing thickness and specific resistance are presented. Based on the experimental data for the HF(DF) lasing spectrum, the coefficient of two-photon absorption in germanium has been estimated as K2 = 55 ± 10 cm/GW at λ = 2.8 μm. The results are in good agreement with theory. The developed experimental data-processing software has enabled the numerical study of the transmission of a high-power beam with λ = 2.6–3 μm through Ge at any laser-pulse-impact moment. It has been shown that thin germanium coatings can efficiently smoothen the distribution of energy over the beam aperture for high-power laser radiation with λ = 2.6–4 μm.

Magnetic correlations and transport properties in triangular-lattice nickel germanide Ni1.8Ge single crystal

Magnetic and transport properties of triangular-lattice Ni1.8Ge single crystal have been studied. The results reveal that Ni1.8Ge is a metal with an obvious magnetic anisotropy. The compound exhibits ferrimagnetic correlations along both directions. However, the long-range magnetic order was not observed due to the geometrical frustration arising from the triangular nickel lattice. At low temperature, the electron-magnon scattering and spin fluctuation have obvious contributions to the resistivity and magnetoresistance, indicating the existence of short-range dynamic magnetic ordering.

Room Temperature Hard Radiation Detectors Based on Solid State Compound Semiconductors: An Overview

Si and Ge single crystals are the most common semiconductor radiation detectors. However, they need to work at cryogenic temperatures to decrease their noise levels. In contrast, compound semiconductors can be operated at room temperature due to their ability to grow compound materials with tunable densities, band gaps and atomic numbers. Highly efficient room temperature hard radiation detectors can be utilized in biomedical diagnostics, nuclear safety and homeland security applications. In this review, we discuss room temperature compound semiconductors. Since the field of radiation detection is broad and a discussion of all compound materials for radiation sensing is impossible, we discuss the most important materials for the detection of hard radiation with a focus on binary heavy metal semiconductors and ternary and quaternary chalcogenide compounds.

Development of the Growth Technology of Highly Homogeneous Semiconductor Crystals

Different technological solutions for growing GaSb(Te) and Ge(Ga) single crystals, making it possible to optimize the growth of highly homogeneous (at the microlevel) semiconductor crystals by the Bridgman method, are described. The possibility of implementing steady-state growth conditions (providing uniform dopant distribution over the crystal) has been experimentally confirmed.

Laser induced surface and structural modification of germanium in liquid environments

Laser-induced surface and structural modifications of germanium (Ge) in liquid environments of deionized water and ethanol have been investigated. Single crystal Ge (100) has been exposed by KrF excimer laser at four different fluences. Scanning electron microscope analysis reveals the formation of cavities, cracks, and ripples in case of ablation in deionized water, whereas the formation of cavities, ridges, and pores is observed in case of ablation in ethanol. The distinctness, density, and size of cavities are significantly larger in deionized water as compared to ethanol. It is attributed to lower absorption coefficient of deionized water (0.2 × 10−2/mm) as compared to ethanol (1.2 × 10−2/mm) for 248 nm, and consequently, more energy deposition to Ge takes place in the case of ablation in deionized water as compared to ethanol. Fourier transform infrared spectroscopy shows the formation of C-H stretching vibration band in case of ethanol at two moderate fluences. Raman spectroscopy reveals that only G...

Effect of the Addition of Silicon on the Properties of Germanium Single Crystals for IR Optics

Homogeneous Sb-doped single crystals of Ge–Si solid solutions are grown with a silicon content of 0.2 to 0.8 at %. The optical absorption of single crystals with a resistivity of (2–3) Ω cm is studied by IR Fourier spectroscopy at a wavelength of 10.6 μm in the temperature range from 25 to 60°C. It is found that the introduction of silicon into antimony-doped germanium improves the temperature stability of the optical properties of the crystals.

Investigation of Subsurface Damage Behaviors in Single-crystal Ge by Multi-cyclic Nanoindentation

Single-crystal Ge shows various machining-induced phase transformation behaviors which are accompanied by significant change of material characteristics. Therefore, revealing the mechanism of phase transformation may open up new ways of developing low-damage machining processes. Although the phase transformation of single-crystal Ge has been investigated in a few previous studies, the mechanisms of phase transformation and crystal defect nucleation are very complicated and still unclear. In this study, multi-cyclic nanoindentation of single-crystal Ge was performed with varying load holding processes to investigate the change of subsurface damaging behaviors. The experimental results showed that phase transformation behaviors of single-crystal Ge were classified into three types according to the holding load. A low holding load promoted phase transformation from dc-Ge to r8-Ge, whereas a middle holding load prevented the phase transformation. At a low holding load, a mixed region of phase transformation and crystal defects was observed around a densely phase-transformed region immediately underneath the indented surface. It was demonstrated that the middle holding load promoted nucleation of wide twins, around which no phase transformation occurred. For a high holding load, however, a densely phase-transformed region was widely formed and phase transformation to r8-Ge was confirmed more frequently than a middle holding load. These results will deepen the understanding of phase transformation and subsurface damaging behaviors of Ge, and contribute to the mechanical machining process optimization.

Computational analysis of heat transfer, thermal stress and dislocation density during resistively Czochralski growth of germanium single crystal

In this paper, a set of numerical simulations of fluid flow, temperature gradient, thermal stress and dislocation density for a Czochralski setup used to grow IR optical-grade Ge single crystal have been done for different stages of the growth process. A two-dimensional steady state finite element method has been applied for all calculations. The obtained numerical results reveal that the thermal field, thermal stress and dislocation structure are mainly dependent on the crystal height, heat radiation and gas flow in the growth system.

Van der Waals epitaxy of Ge films on mica

To date, many materials have been successfully grown on substrates through van der Waals epitaxy without adhering to the constraint of lattice matching as is required for traditional chemical epitaxy. However, for elemental semiconductors such as Ge, this has been challenging and therefore it has not been achieved thus far. In this paper, we report the observation of Ge epitaxially grown on mica at a narrow substrate temperature range around 425 °C. Despite the large lattice mismatch (23%) and the lack of high in-plane symmetry in the mica surface, an epitaxial Ge film with [111] out-of-plane orientation is observed. Crystallinity and electrical properties degrade upon deviation from the ideal growth temperature, as shown by Raman spectroscopy, X-ray diffraction, and Hall effect measurements. X-ray pole figure analysis reveals that there exist multiple rotational domains in the epitaxial Ge film with dominant in-plane orientations between Ge1¯10 and mica[100] of (20n)°, where n = 0, 1, 2, 3, 4, 5. A superlattice area mismatch model was used to account for the likelihood of the in-plane orientation formation and was found to be qualitatively consistent with the observed dominant orientations. Our observation of Ge epitaxy with one out-of-plane growth direction through van der Waals forces is a step toward the growth of single crystal Ge films without the constraint in the lattice and symmetry matches with the substrates.

Nonlinear absorption of non-chain HF laser radiation in germanium

The transmission of high-power HF(DF) laser radiation through Ge single crystals of different quality has been experimentally and numerically investigated. Based on the experimental data for the lasing spectrum, the two-photon absorption coefficient in Ge is estimated to be K2 =55±10 cmGW−1 at λ=2.8μm. The transmission dynamics of high-power radiation with λ=2.6−3 μm through germanium crystals is numerically simulated.

Effects of temperature on the ion-induced bending of germanium and silicon nanowires

Nanowires can be manipulated using an ion beam via a phenomenon known as ion-induced bending (IIB). While the mechanisms behind IIB are still the subject of debate, accumulation of point defects or amorphisation are often cited as possible driving mechanisms. Previous results in the literature on IIB of Ge and Si nanowires have shown that after irradiation the aligned nanowires are fully amorphous. Experiments were recently reported in which crystalline seeds were preserved in otherwise-amorphous ion-beam-bent Si nanowires which then facilitated solid-phase epitaxial growth (SPEG) during subsequent annealing. However, the ion-induced alignment of the nanowires was lost during the SPEG. In this work, in situ ion irradiations in a transmission electron microscope at 400 °C and 500 °C were performed on Ge and Si nanowires, respectively, to supress amorphisation and the build-up of point defects. Both the Ge and Si nanowires were found to bend during irradiation thus drawing into question the role of mechanisms based on damage accumulation under such conditions. These experiments demonstrate for the first time a simple way of realigning single-crystal Ge and Si nanowires via IIB whilst preserving their crystal structure.