Aug 16, 2019

Characteristics of strained-germanium p- and n-channel field effect transistors on a Si (1 1 1) substrate

Characteristics of strained-germanium (Ge) p- and n-channel field effect transistors directly on Si (1 1 1) substrates have been investigated. A strained-Ge layer with a thickness of ~4 nm has been grown on the relaxed Si/Si (1 1 1) substrate by ultra-high-vacuum chemical vapour deposition. To improve the oxide/strained-Ge interface, a thin Si-cap layer with a thickness of 3 nm has been grown on the strained-Ge layer. After the device process, 1 nm thickness of Si-cap layer remains on the strained-Ge layer. Thicknesses of all epitaxial layers have been measured by transmission electron microscopy. Raman spectroscopy measurement on the Si-cap/strained-Ge layer shows that the strained-Ge layer has a compressive strain of ~1.25%. A hole confinement shoulder on the capacitance–voltage curve at the accumulation region has been observed due to carrier confinement at the Si-cap/strained-Ge hetero-interface. A metal–oxide–semiconductor (MOS) structure on the strained-Ge layer shows a moderate interface trap charge density of ~2.8 × 1011 cm−2 eV−1. Strained-Ge p- and n-channel field effect transistors show low off-state leakage currents of ~3.8 × 10−13 A µm−1 and ~6.5 × 10−13 A µm−1, respectively. Drive currents of strained-Ge p- and n-channel field effect transistors are enhanced by ~100% and ~40%, respectively, as compared with bulk Si (1 1 1) transistors. Peak hole and electron mobility of strained-Ge (1 1 1) field effect transistors at the low effective field are found to be ~110% and ~30% enhancement, respectively, as compared with bulk Si (1 1 1) transistors, due to high hole and electron mobility enhancement factor as well as strain-induced lower conduction mass in the strained-Ge channel.



Source:IOPscience
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Aug 9, 2019

Investigation of amorphous germanium contact properties with planar detectors made from USD-grown germanium crystals

The characterization of detectors fabricated from home-grown crystals is the most direct way to study crystal properties. We fabricated planar detectors from high-purity germanium (HPGe) crystals grown at the University of South Dakota (USD). In the fabrication process, a HPGe crystal slice cut from a USD-grown crystal was coated with a high resistivity thin film of amorphous Ge (a-Ge) followed by depositing a thin layer of aluminum on top of the a-Ge film to define the physical area of the contacts. We investigated the detector performance including the I-V characteristics, C-V characteristics and spectroscopy measurements for a few detectors. The results document the good quality of the USD-grown crystals and electrical contacts.


Source:IOPscience
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Aug 1, 2019

Thin germanium–carbon layers deposited directly on silicon for metal–oxide–semiconductor devices

We report the growth process and materials characterization of germanium–carbon alloys (Ge1−xCx) deposited directly on Si (1 0 0) substrates by ultra-high-vacuum chemical vapour deposition. The Ge1−xCx films are characterized by transmission electron microscopy, etch-pit density, x-ray diffraction, secondary ion mass spectrometry and electron energy loss spectroscopy. The results show that the films exhibit low threading dislocation densities despite significant strain relaxation. We also present evidence for carbon segregation in the Ge1−xCx and interpret these results as a strain relaxation mechanism.



Source:IOPscience
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Jul 23, 2019

Temperature-independent slow carrier emission from deep-level defects in p-type germanium

In the deep-level transient spectroscopy (DLTS) spectra of the 3d-transition metals cobalt and chromium in p-type germanium, evidence is obtained that hole emission from defect levels can occur by two parallel paths. Besides classical thermal emission, we observed a second, slower and temperature-independent emission. We show that this extra emission component allows determining unambiguously whether or not multiple DLTS peaks arise from the same defect. Despite similar characteristics, we demonstrate that the origin of the non-thermal emission is not tunnelling but photoionization related to black-body radiation from an insufficiently shielded part of the cryostat.



Source:IOPscience
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Jul 17, 2019

Heat capacity of germanium crystals with various isotopic composition

The heat capacity of three pure (n, p2×1016 cm-3) germanium crystals with different isotopic compositions was measured in the temperature range from 2.8 K to 100 K. These samples, one made of enriched 70Ge (95.6%), Ge of natural isotopic composition and n, p < 1014 cm-3, and one of the largest possible isotopic mass variance 70/76Ge (43%/48%) with n, p<1014 cm-3, show a change of the molar heat capacity (and corresponding Debye temperature, θD) as expected from the average mass variation, corresponding to θDM-0.5 (M = molar mass) at low temperatures. The mass effect is best visible around 21.5 K, at the minimum of the corresponding Debye temperatures θD, and amounts to ΔθD = 5.3 K for the difference between the Debye temperatures of 70Ge and 70/76Ge. The specific heat capacity of the natural Ge crystal agrees within 2% with the best data available in the literature taken on much larger masses of Ge.



Source:IOPscience
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Jul 9, 2019

Highly boron-doped germanium layers on Si(001) grown by carbon-mediated epitaxy

Smooth and fully relaxed highly boron-doped germanium layers were grown directly on Si(001) substrates using carbon-mediated epitaxy. A doping level of  was measured by several methods. Using high-resolution x-ray diffraction we observed different lattice parameters for intrinsic and highly boron-doped samples. A lattice parameter of a Ge:B = 5.653 Å was calculated using the results obtained by reciprocal space mapping around the (113) reflection and the model of tetragonal distortion. The observed lattice contraction was adapted and brought in accordance with a theoretical model developed for ultra-highly boron-doped silicon. Raman spectroscopy was performed on the intrinsic and doped samples. A shift in the first order phonon scattering peak was observed and attributed to the high doping level. A doping level of  was calculated by comparison with literature. We also observed a difference between the intrinsic and doped sample in the range of second order phonon scattering. Here, an intense peak is visible at  for the doped samples. This peak was attributed to the bond between germanium and the boron isotope 11B.



Source:IOPscience
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Jul 5, 2019

Unified model of diffusion of interstitial oxygen in silicon and germanium crystals

A theoretical modelling of the oxygen diffusivity in silicon and germanium 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 ΔEa(Si) = 2.59 eV, ΔEa(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 (P80 kbar) results in a linear decrease of the diffusion barrier (\partial_P \Delta E_{\mathrm {a}} (P)=-4.38\times 10^{-3}~{\mathrm {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.


Source:IOPscience
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Jun 20, 2019

Vertically oriented epitaxial germanium nanowires on silicon substrates using thin germanium buffer layers

We demonstrate a method to realize vertically oriented Ge nanowires on Si(111) substrates. Ge nanowires were grown by chemical vapor deposition using Au nanoparticles to seed nanowire growth via a vapor–liquid–solid growth mechanism. Rapid oxidation of Si during Au nanoparticle application inhibits the growth of vertically oriented Ge nanowires directly on Si. The present method employs thin Ge buffer layers grown at low temperature less than 600 °C to circumvent the oxidation problem. By using a thin Ge buffer layer with root-mean-square roughness of ~ 2 nm, the yield of vertically oriented Ge nanowires is as high as 96.3%. This yield is comparable to that of homoepitaxial Ge nanowires. Furthermore, branched Ge nanowires could be successfully grown on these vertically oriented Ge nanowires by a secondary seeding technique. Since the buffer layers are grown under moderate conditions without any high temperature processing steps, this method has a wide process window highly suitable for Si-based microelectronics.


Source:IOPscience
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Jun 14, 2019

Investigation of Surface Roughness of Single Point Diamond Turned Germanium Substrate by Coherence Correlation Interferometry and Image Processing

Germanium is a widely used material in the infrared range. Single crystal germanium is used as semiconductor and optical material due to its salient features like high refractive index and proper working in cryogenic conditions. Thus, germanium is an important substrate for infrared lens having many applications in thermal imaging cameras, optical telescopes and miniaturization of infrared optical elements. These applications require optical elements of excellent surface quality and high dimensional accuracy. In addition to fulfil the demands, ultraprecision machine is used to fabricate the optical components. In this work, single crystal germanium (111) mirror is fabricated by using single point diamond tool with, negative rake angle. A large number of experiments are performed to achieve the surface finish of nanometric range. The best and worst combinations of process parameters are found on the basis of surface roughness with the help of coherence correlation interferometry(CCI) measurement and image processing using Canny, Prewitt, Roberts and Sobel edge filters and histogram. These results can be used for fabrication of diffractive optical elements and aspheric lenses of germanium.


Source:IOPscience
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Jun 5, 2019

Investigation of the electrical performance of hfo2 dielectrics deposited on passivated germanium substrates

Propanethiol solution (0.1 M) in 2-propanol, octanethiol solution (0.1 M) in 2-propanol and 20% (NH4)2S solution in water were used to passivate the germanium substrates. HfO2 thin films of 150 ALD cycles were then deposited on the passivated germanium substrates. The morphology of the thin films was investigated by X-ray diffraction and it was found that the morphology of the thin films was not affected by the chemical treatments. A lower leakage current density was observed in the passivated samples compared with the witness one. In addition, the interface quality and long-time stress reliability of the passivated samples were improved when the samples were annealed in forming gas ambient.


Source:IOPscience
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May 28, 2019

Self-diffusion in intrinsic germanium and effects of doping on self-diffusion in germanium

Self-diffusion in intrinsic germanium single crystals has been investigated over the temperature range 822-1163K using 71Ge as radioisotope and a sputtering technique for serial sectioning. The data can be described by a preexponential factor of (2.48+or-0.6)*10-3 m2 s-1 and an activation enthalpy of (3.14+or-0.92) eV. The present data are discussed together with literature data obtained with conventional sectioning techniques at higher temperatures. The self-diffusion coefficients at 870 and 894K were also measured for Ga-doped (1.7*1018 atoms cm-3) and Sb-doped (1.8*1018 atoms cm-3) samples. The diffusivity is higher in n-type and lower in p-type germanium than in intrinsic material. Since it is known that a vacancy in germanium acts as an acceptor the observed direction and order of magnitude of the doping dependence can be understood in terms of the shift of the Fermi level in doped crystals. This supports the view that self-diffusion in germanium proceeds by a vacancy mechanism.


Source:IOPscience
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May 23, 2019

Ultralarge transient optical gain from tensile-strained, n-doped germanium on silicon by spin-on dopant diffusion

The direct band gap optical gain of tensile-strained, highly n-doped germanium on silicon is investigated by femtosecond ultrafast transmittance spectroscopy. A germanium film with 0.22% tensile strain is grown on a silicon substrate by using molecular beam epitaxy. An activated doping concentration up to 4 × 1019 cm−3 is achieved by phosphorus diffusion from a spin-on dopant source. The transmittance of the germanium film is clearly increased upon increasing the pump power. A peak optical gain of up to 5300 cm−1 around 1.7 µm and a gain spectrum broader than 300 nm are obtained. These results show a simple yet promising way to realize gain medium for monolithic-integrated germanium lasers.


Source:IOPscience
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May 14, 2019

Infrared and terahertz transmission properties of germanium single crystals

Experimental transmission spectra of samples fabricated of germanium single crystals doped with stibium were registered in the infrared 2.5-25 μm and terahertz 130 μm regions of spectrum. It is shown that doping concentration and treatment of the crystals surface have a noticeable influence on the samples absorption.


Source:IOPscience
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May 9, 2019

Germanium layers grown by zone thermal crystallization from a discrete liquid source

It is proposed and investigated a method for growing thin uniform germanium layers onto large silicon substrates. The technique uses the hexagonally arranged local sources filled with liquid germanium. Germanium evaporates on very close substrate and in these conditions the residual gases vapor pressure highly reduces. It is shown that to achieve uniformity of the deposited layer better than 97% the critical thickness of the vacuum zone must be equal to l cr = 1.2 mm for a hexagonal arranged system of round local sources with the radius of r = 0.75 mm and the distance between the sources of h = 0.5 mm.



Source:IOPscience
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Apr 30, 2019

The impact of polishing on germanium-on-insulator substrates

We prepared germanium-on-insulator (GOI) substrates by using Smart-Cut™ and wafer bonding technology. The fabricated GOI is appropriate for polishing due to a strong bonding strength (2.4 MPa) and a sufficient bonding quality. We investigated mechanical polishing and chemical—mechanical polishing (CMP) systematically, and an appropriate polishing method—mechanical polishing combined with CMP—is obtained. As shown by AFM measurement, the RMS of GOI after polishing decreased to 0.543 nm. And the Ge peak profile of the XRD curve became symmetric, and the FWHM is about 121.7 arcsec, demonstrating a good crystal quality.


Source:IOPscience
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Apr 23, 2019

Spin-on doping of germanium-on-insulator wafers for monolithic light sources on silicon

High electron doping of germanium (Ge) is considered to be an important process to convert Ge into an optical gain material and realize a monolithic light source integrated on a silicon chip. Spin-on doping is a method that offers the potential to achieve high doping concentrations without affecting crystalline qualities over other methods such as ion implantation and in-situ doping during material growth. However, a standard spin-on doping recipe satisfying these requirements is not yet available. In this paper we examine spin-on doping of Ge-on-insulator (GOI) wafers. Several issues were identified during the spin-on doping process and specifically the adhesion between Ge and the oxide, surface oxidation during activation, and the stress created in the layers due to annealing. In order to mitigate these problems, Ge disks were first patterned by dry etching followed by spin-on doping. Even by using this method to reduce the stress, local peeling of Ge could still be identified by optical microscope imaging. Nevertheless, most of the Ge disks remained after the removal of the glass. According to the Raman data, we could not identify broadening of the lineshape which shows a good crystalline quality, while the stress is slightly relaxed. We also determined the linear increase of the photoluminescence intensity by increasing the optical pumping power for the doped sample, which implies a direct population and recombination at the gamma valley.


Source:IOPscience
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Apr 18, 2019

Room-temperature direct bonding of germanium wafers by surface-activated bonding method

This paper reports the mechanical and electrical characteristics of Ge/Ge interfaces prepared by room-temperature surface-activated bonding (SAB). Bonded Ge/Ge wafer pairs with high bonding strength equivalent to that of the bulk material were achieved without any heat treatment. It was found that the bonding of Ge wafers was not sensitive to the background vacuum pressure in a wafer-bonding chamber compared with the bonding of Si wafers. The current–voltage characteristics and microstructures of bonded interfaces formed by SAB and low-temperature plasma activation bonding (PAB) were compared. It was demonstrated that junctions with very low resistivity can be obtained by SAB at room temperature


Source:IOPscience
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Apr 9, 2019

Characteristics of Germanium-on-Insulators Fabricated by Wafer Bonding and Hydrogen-Induced Layer Splitting

There is considerable interest in germanium-on-insulator (GeOI) because of its advantages in terms of device performance and compatibility with silicon processing. In this paper, fabricating GeOI by hydrogen-induced layer splitting and wafer bonding is discussed. Hydrogen in germanium exists in molecular form and is prone to outdiffusion, resulting in a storage-time dependence of blistering. In contrast to the case of silicon, little effect of substrate doping on blistering is observed in germanium. Hydrogen implantation in germanium creates both {100}- and {111}-type microcracks. These two types of platelets are located in the same region for (111)-oriented wafers, but in different zones for (100) samples. This variation in distribution explains the smoother splitting of (111) surfaces than that of (100) surfaces. Hydrogen implantation also introduces a significant concentration of charged vacancies, which affect dopant diffusion in the transferred germanium film. Boron, with a negligible Fermi-level dependence, shows an identical diffusion profile to that of bulk germanium. In contrast, phosphorus diffusion is enhanced in the fabricated GeOI layers. These results also shed light on the understanding of dopant diffusion mechanisms in germanium.




Source:IOPscience
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Apr 3, 2019

Effects of the chemical bonding on the optical and mechanical properties for germanium carbide films used as antireflection and protection coating of ZnS windows

Germanium carbide (Ge1−xCx) films have been prepared by RF reactive sputtering a pure Ge(111) target at different flow rate ratios of CH4/(CH4+Ar) in a CH4/Ar mixture discharge, and it has been found that the composition, chemical bonding, optical and mechanical properties of Ge1−xCx films are remarkably influenced by the flow rate ratio of CH4/(CH4+Ar). The effects of the chemical bonding on the optical and mechanical properties of the Ge1−xCx films have been explored. In addition, an antireflection Ge1−xCx double-layer coating deposited on both sides of the ZnS substrate wafer has been developed for application as an infrared window. It is shown that the transmittance in the wavelength region between 8 and 12 µm and the hardness of the ZnS substrate have been significantly improved by the double-layer coating.



Source:IOPscience
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Mar 25, 2019

The measured positive and negative magnetoresistance for n-type germanium at room temperature

Magnetoresistance (MR) for n-type germanium wafers by in-line-four-terminal method at room temperature are explored. Conspicuously, the variation of the measured MR as a function of applied current and voltage-terminal separation is observed. With a further increase of applied current, the measured MR initially increases, passes through a peak value at a certain current and then finally decreases. The measured MR increases with an increase of the value of voltage-terminal separation. The most important outcome of this study is the observation of negative MR for the smallest voltage-terminal separation of 2 µm, and the sign change of the measured MR can be achieved by magnetic fields. These interesting results may lead to an alternative approach to future magneto-electronic devices.



Source:IOPscience
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Mar 18, 2019

Annealing Effects on Ge/SiO2 Interface Structure in Wafer-Bonded Germanium-on-Insulator Substrates

We have investigated annealing effects on Ge/SiO2 interfaces in wafer-bonded germanium-on-insulator substrates using transmission electron microscopy and electron energy loss spectroscopy. A number of nanometer-sized hollows were observed at the Ge/SiO2 interfaces after annealing at 500 and 600 °C, while the density of these hollows was very small after annealing at 700 and 800 °C. The hollows are attributed to the formation of amorphous oxides of Si-rich Si1-xGexO2. The mechanism for the formation and disappearance of these amorphous hollows on the Ge substrates is discussed.



Source:IOPscience
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Mar 12, 2019

Thin film germanium on silicon created via ion implantation and oxide trapping

We present a novel process for integrating germanium with (SOI)  silicon-on-insulator wafers. Germanium is implanted into SOI which is then oxidized, trapping the germanium between the two oxide layers (the grown oxide and the buried oxide). With careful control of the implantation and oxidation conditions this process creates a thin layer (current experiments indicate up to 20-30nm) of almost pure germanium. The layer can be used potentially for fabrication of integrated photo-detectors sensitive to infrared wavelengths, or may serve as a seed for further germanium growth. Results are presented from electron microscopy and Rutherford back-scattering analysis, as well as preliminary modelling using an analytical description of the process.


Source:IOPscience
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Mar 5, 2019

Fabrication of Ge-on-insulator wafers by Smart-CutTM with thermal management for undamaged donor Ge wafers

Newly engineered substrates consisting of semiconductor-on-insulator are gaining much attention as starting materials for the subsequent transfer of semiconductor nanomembranes via selective etching of the insulating layer. Germanium-on-insulator (GeOI) substrates are critically important because of the versatile applications of Ge nanomembranes (Ge NMs) toward electronic and optoelectronic devices. Among various fabrication techniques, the Smart-CutTM technique is more attractive than other methods because a high temperature annealing process can be avoided. Another advantage of Smart-CutTM is the reusability of the donor Ge wafer. However, it is very difficult to realize an undamaged Ge wafer because there exists a large mismatch in the coefficient of thermal expansion among the layers. Although an undamaged donor Ge wafer is a prerequisite for its reuse, research related to this issue has not yet been reported. Here we report the fabrication of 4-inch GeOI substrates using the direct wafer bonding and Smart-CutTM process with a low thermal budget. In addition, a thermo-mechanical simulation of GeOI was performed by COMSOL to analyze induced thermal stress in each layer of GeOI. Crack-free donor Ge wafers were obtained by annealing at 250 °C for 10 h. Raman spectroscopy and x-ray diffraction (XRD) indicated similarly favorable crystalline quality of the Ge layer in GeOI compared to that of bulk Ge. In addition, Ge p-n diodes using transferred Ge NM indicate a clear rectifying behavior with an on and off current ratio of 500 at ±1 V. This demonstration offers great promise for high performance transferrable Ge NM-based device applications.



Source:IOPscience
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Feb 18, 2019

Topography and lattice parameter of Si:Ge bulk crystals

X-ray topographic and chemical etching examination of Si:Ge single crystals containing 1.2 at% and 3.0 at% Ge, together with precise lattice parameter measurements, was performed. Diffraction contrasts in the form of concentric `quasi-circles' (striations), probably due to the non-uniform distribution of Ge atoms, were observed in projection topographs. The etching patterns revealed bands corresponding to striations and dislocations as etch pits. The central `core' crystal region (striation-free) exhibited a crystal lattice strongly disturbed by microdefects, as was concluded from the section topography analysis. The lattice parameter measurements have shown the non-uniformity of the distribution of Ge atoms across the samples.


Source:IOPscience
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Feb 11, 2019

Electronic properties of manganese impurities in germanium

The electronic properties of manganese in crystalline germanium have been investigated by means of deep level transient spectroscopy (DLTS). Mn was diffused in the material by a thermal treatment at 700 °C. Next to the deep levels of nickel and copper, which are known contaminants in Ge treated at high temperature, three not previously reported levels were observed. These two hole and one electron traps, with apparent energy level positions at EV +0.136 eV, EV +0.342 eV and EC − 0.363 eV, were assigned to substitutional Mn. The analysis of the carrier capture cross-sections, the absence of field-assisted emission and the observation of the Mn2− electron paramagnetic resonance spectrum in n-type Ge:Mn at low temperature are all compatible with Mn introducing two acceptor and one donor levels in the band gap of Ge.







Source:IOPscience
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Jan 29, 2019

Electrogyration and Faraday rotation in pure and Cr-doped lead germanate crystals

We present the results of studies on the temperature dependence of the electrogyration (EG) effect, Faraday rotation and natural optical activity in Pb5Ge3O11 and Pb5Ge3O11:Cr crystals at the phase transition. A high EG coefficient is found for Pb5Ge3O11:Cr crystals. We demonstrate how the Curie–Weiss constant, the critical exponents of the order parameter and the dielectric permittivity in Pb5Ge3O11:Cr crystals, as well as the coefficients of thermodynamic potential, could be derived from the temperature dependences of optical activity and the EG coefficient. We also show that the increment of the Faraday rotation in Pb5Ge3O11 and Pb5Ge3O11:Cr crystals appearing at the phase transition is caused by a combined magneto-electrooptic effect induced by spontaneous polarization. It is proportional to the square of spontaneous polarization. The phenomenon revealed by us corresponds to combined effects of crystal optics, which appear due to the common action of different fields.



Source:IOPscience

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Jan 20, 2019

Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction


The analysis of threading dislocation density (TDD) in Ge-on-Si layer is critical for developing lasers, light emitting diodes (LEDs), photodetectors (PDs), modulators, waveguides, metal oxide semiconductor field effect transistors (MOSFETs), and also the integration of Si-based monolithic photonics. The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope (TEM). However, high-resolution x-ray diffraction (HR-XRD) rocking curve provides an optional method to analyze the TDD in Ge layer. The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors. In this paper, this method is extended to the case of strained Ge-on-Si layers. The HR-XRD  scan is measured and Ge (004) single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer. The rocking curve full width at half maximum (FWHM) broadening by incident beam divergence of the instrument, crystal size, and curvature of the crystal specimen is subtracted. The TDDs of samples A and B are calculated to be 1.41 × 108 cm−2 and 6.47 × 108 cm−2, respectively. In addition, we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer. 



Source:IOPscience

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Jan 14, 2019

Germanium epitaxy on silicon


With the rapid development of on-chip optical interconnects and optical computing in the past decade, silicon-based integrated devices for monolithic and hybrid optoelectronic integration have attracted wide attention. Due to its narrow pseudo-direct gap behavior and compatibility with Si technology, epitaxial Ge-on-Si has become a significant material for optoelectronic device applications. In this paper, we describe recent research progress on heteroepitaxy of Ge flat films and self-assembled Ge quantum dots on Si. For film growth, methods of strain modification and lattice mismatch relief are summarized, while for dot growth, key process parameters and their effects on the dot density, dot morphology and dot position are reviewed. The results indicate that epitaxial Ge-on-Si materials will play a bigger role in silicon photonics.


Source:IOPscience

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Jan 8, 2019

Research progress of Si-based germanium materials and devices


Si-based germanium is considered to be a promising platform for the integration of electronic and photonic devices due to its high carrier mobility, good optical properties, and compatibility with Si CMOS technology. However, some great challenges have to be confronted, such as: (1) the nature of indirect band gap of Ge; (2) the epitaxy of dislocation-free Ge layers on Si substrate; and (3) the immature technology for Ge devices. The aim of this paper is to give a review of the recent progress made in the field of epitaxy and optical properties of Ge heterostructures on Si substrate, as well as some key technologies on Ge devices. High crystal quality Ge epilayers, as well as Ge/SiGe multiple quantum wells with high Ge content, were successfully grown on Si substrate with a low-temperature Ge buffer layer. A local Ge condensation technique was proposed to prepare germanium-on-insulator (GOI) materials with high tensile strain for enhanced Ge direct band photoluminescence. The advances in formation of Ge n+p shallow junctions and the modulation of Schottky barrier height of metal/Ge contacts were a significant progress in Ge technology. Finally, the progress of Si-based Ge light emitters, photodetectors, and MOSFETs was briefly introduced. These results show that Si-based Ge heterostructure materials are promising for use in the next-generation of integrated circuits and optoelectronic circuits.


Source:IOPscience

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