Ge Diffusion Research Articles

Diffusion of Ge Donors in β‐Ga2O3

Diffusion of Ge donors in β‐Ga2O3 is studied using a combination of secondary‐ion mass spectrometry, diffusion simulations, and first‐principles calculations, and compared to previous studies on Sn diffusion. Ge is implanted into (01)‐oriented samples and annealed at temperatures from 900 to 1050 °C for a total of 8 h. From previous first‐principles calculations, Sn is predicted to diffuse via the formation of a mobile complex with VGa that migrates through a sequence of exchange and rotation jumps. Herein, it is similarly predicted that Ge diffusion is mediated by VGa. However, the microscopic mechanism differs, as Ge can diffuse more easily through exchange combined with complex dissociation, rather than rotational jumps. This is explained by the difference in Ga‐site preference of Ge compared to Sn, and the three‐split mechanism that enables low migration barriers for VGa. The dissociation mechanism leads to a considerably faster transport for Ge as compared to Sn. The experimentally obtained Ge diffusion profiles are successfully fitted using a reaction–diffusion model based on the predicted diffusion mechanism, yielding a migration barrier of 2.5 ± 0.2 eV for the complex. The 2.72 eV obtained from first‐principles calculations is in good agreement with this value.

Development of nano-porous Au thin film at room temperature via ion irradiation in a-Ge/Au bilayer system followed by chemical etching of Ge

The development of nano-porous gold (NPG) via room temperature ion irradiation has been presented in detail. The bilayer thin films of a-Ge/c-Au have been irradiated by 100 MeV Ni ions with the fluence of 5 × 1013 ions cm−2 at room temperature. NPG is obtained by selectively etching Ge off from the Au matrix by dipping the Ge/Au thin film into 10 % H2O2 solution. Diffusion of Ge and Au across the interface under irradiation was confirmed by TRIM simulation and RBS spectra. The SEM image and EDX spectra confirms the formation of NPG with high purity. In addition, the statistical and fractal analysis of AFM image also confirms the formation of NPG. NPG system has been observed to show very good optical properties (low reflectance and high transmittance). The high quality NPG prepared by this method can be useful in the fields like optical sensors, transparent conductive electrodes, anti-reflective coatings, and photo-detector technology.

Semi-quantitative μLIBS mapping of germanium diffusion between metal and silicate during planetary core–mantle segregation

Understanding the distribution of elements between the cores and mantles of planetary bodies is essential for elucidating the geological and geochemical processes operating during their formation. Because the semi-metallic element Ge shows complex siderophile, chalcophile, and lithophile properties, it is particularly significant for investigating core–mantle segregation and ore deposit formation. Recent advancements in in situ microanalysis techniques, such as μLIBS, have enabled high-resolution elemental mapping of Ge and other trace elements.This study explores the application of μLIBS imaging to investigate the high-temperature/high-pressure distribution of Ge between metallic and silicate matrices analogous to planetary cores and mantles. By cross-calibrating the μLIBS intensities with electron microprobe profile analyses carried out on piston cylinder experimental samples, we produced semi-quantitative Ge maps from which we extracted Ge concentration profiles to assess Ge diffusion from the silicate to the metal. We determined, for the first time, the diffusion coefficient of Ge between metal and silicate to be D(Ge)metal = 4.03E−13 ± 3.6E−14 m2/s at 1 GPa and 1350 °C. Our results demonstrate the capability and efficiency of μLIBS for providing detailed, high-resolution (15 μm) trace element concentration data at few ppm levels, offering a time- and cost-effective alternative to conventional techniques.These findings bring insights on planetesimal differentiation and on chemical exchanges between metal and silicate phases in a magma ocean and between two different metal phases occurring at the bottom of the magma ocean during planetesimal formation.

Controllable preparation of carbon coating Ge nanospheres with a cubic hollow structure for high-performance lithium ion batteries

Germanium based nanomaterials are very promising as the anodes for the lithium ion batteries since their large specific capacity, excellent lithium diffusivity and high conductivity. However, their controllable preparation is still very difficult to achieve. Herein, we facilely prepare a unique carbon coating Ge nanospheres with a cubic hollow structure (Ge@C) via a hydrothermal synthesis and subsequent pyrolysis using low-cost GeO2 as precursors. The hollow Ge@C nanostructure not only provides abundant interior space to alleviate the huge volumetric expansion of Ge upon lithiation, but also facilitates the transmission of lithium ions and electrons. Moreover, experiment analyses and density functional theory (DFT) calculations unveil the excellent lithium adsorption ability, high exchange current density, low activation energy for lithium diffusion of the hollow Ge@C electrode, thus exhibiting significant lithium storage advantages with a large charge capacity (1483 mAh/g under 200 mA g−1), distinguished rate ability (710 mAh/g under 8000 mA g−1) as well as long-term cycling stability (1130 mAh/g after 900 cycles under 1000 mA g−1). Therefore, this work offers new paths for controllable synthesis and fabrication of high-performance Ge based lithium storage nanomaterials.

Thermodynamic modelling application for prediction of diffusion formation of supersaturation solution

Abstract In this paper the effect of diffusion formation of supersaturated solid solution in the Al–Ge system is discussed. It was shown that at relatively low temperatures of diffusion annealing, Ge concentration in Al-based solid solution became higher than the solubility limit at given temperatures. The maximal concentration of Ge was determined by extrapolation of the diffusion profile on the Ge/Al interface. Analysis of diffusivity of Al in Ge allowed to suggest that slow diffusion in Ge restricts the formation of Ge-based solid solution. Qualitative approach confirmed this suggestion.

Computational model for predicting structural stability and stress transfer of a new SiGe stressor technique for NMOS devices

A new method to induce tensile stress in a PDSOI NMOS device for RF applications is proposed, which is based on relaxing a SiGe layer built underneath silicon. By means of TCAD simulations, we demonstrate that stress transfer from SiGe to Si occurs by means of at least two different mechanisms: SiGe relaxation due to amorphization and the formation of Stacking Faults during recrystallization. By considering both phenomena, a tensile stress of 0.5 GPa can be injected into the silicon channel. Moreover, the impact of annealing steps on the detrimental out-of-SiGe Ge diffusion has been simulated by considering an inter-diffusion model, showing the importance of adapting the PDSOI process flow to account for the presence of the new stressor.

A comparison of Ge, Sb and Te thermal diffusion through Ge2Sb2Te5

Chalcogenide Ge-Sb-Te alloys are used in a new generation of nonvolatile memories named Phase Change Memories which can be thermally switched from low resistivity to high resistivity states by feeding the memory cells with appropriate electrical pulses. During their lifetime, the heterogeneous redistribution of the elements within the active region of the cells is at the origin of the drift of their electrical characteristics and, ultimately, of their failure. Up to now, little is known about the relative diffusivities of the atomic elements that compose the alloys, what hampers the modeling and optimization of the materials and devices. Here, we report an experimental study of the thermal diffusion of Ge, Sb and Te through Ge2Sb2Te5. For this purpose, specific structures consisting of a layer of Ge, Sb or Te sandwiched between two Ge2Sb2Te5 layers have been fabricated and annealed at various temperatures and times. Using transmission electron microscopy based techniques, we evidence that Te diffusion can be activated from about 160 °C while Ge and Sb needs much higher temperatures, 220 °C and 350 °C, respectively. These results are in disagreement with previous theoretical simulations predicting that Ge is the most diffusive element while Te is the least.

Stacked SiGe/Si I/O FinFET device preparation in a vertically stacked gate-all-around technology

In this work, a stacked SiGe/Si input-output (I/O) FinFET device preparation with an optimized thermal budget and atomic layer deposition (ALD) SiO2 gate dielectric is investigated. First, a vertical and smooth profile of the stacked SiGe/Si fin without obvious Ge diffusion and SiGe oxidation is maintained by developing an optimized STI densification process using rapid thermal annealing (RTA) of 850 °C for 30s. Then, a high-quality ALD SiO2 with thickness of 3 nm suitable for the gate dielectric layer of I/O device is verified based on MOS capacitance (CAP) structure. Finally, a stacked SiGe/Si I/O FinFET targeting 1.8V operating voltage (VDD) is successfully prepared with good physical structure and electrical characteristics. Meanwhile, its maximum operating voltage (Vmax) for a 10 years lifetime at a failure rate of 0.01% can reach to 2.03V. Therefore, these newly developed processes are practical for the stacked SiGe/Si I/O FinFET device in a vertically stacked GAA technology.

Concurrent Characterization of Surface Diffusion and Intermixing of Ge on Si: A Classical Molecular Dynamics Study

AbstractThe surface diffusion and intermixing of Ge ad‐atoms over Si (001) 2 × 1 substrates using classical molecular dynamics (CMD) simulations are characterized here. Several interatomic potentials, parametrizations, and parameter mixing rules are contemplated. A novel simulation scheme is devised to characterize the effective frequency of surface diffusion and intermixing events overcoming the inherent difficulties related to their interdependency in heteroepitaxial systems. The effective energy barriers of these events encompass different atomistic mechanisms weighted by their occurrence probabilities. The overall description of surface diffusion and intermixing based on Stillinger–Weber (SW) potential is in agreement with ab initio calculations and experimental observations, though some atomistic details differ. This study is extended to Si(001) substrates with stressed Ge monolayers grown on top. It is found that Ge ad‐atom dynamics is accelerated with respect to the case of the pure Si substrate and that diffusion across dimer rows is mainly mediated by the atomic exchange of the Ge ad‐atom with a Ge atom on the surface.

Formation of crystalline Si1-xGex top layers by ion implantation in crystalline silicon

Semiconductor nanocrystals incorporated in a dielectric film are widely studied as potential candidates to exceed the Shockley-Queisser theoretical conversion limit of photovoltaic cells. In this context, Ge nanocrystals embedded in SiO2 films seem to be among the best candidates. However, the charges generated in the dielectric film are hard to collect. For this reason, it would be better if the charges were generated in a semiconductor matrix such as silicon, which has better conductivity. However, implanted Ge atoms have poor mobility in a silicon matrix and thus Ge nanocrystals formation is not likely. But even if the formation of Ge nanocrystals seems difficult, it would still be interesting to form crystalline Si1-xGex alloys. This work investigates the formation of the Si1-xGex films by ion implantation and their crystallinity. 36 keV Ge ions were implanted in crystalline Si substrates, with fluences ranging from 5 × 1015 to 1.5 × 1017 Ge/cm2 at temperatures up to 600 °C. Rutherford Backscattering Spectrometry (RBS), Raman Spectroscopy, and Transmission Electron Microscopy (TEM) were used to investigate the microstructure of the Si1-xGex alloys. It is shown that germanium is mostly incorporated in the crystal network in substitutional sites. XRD, Raman spectroscopy, and TEM confirm that the Si1-xGex layer on top of the c-Si substrate is monocrystalline. TEM also indicates the possible presence of nanostructures, extended defects or both. Implantation was also carried out at temperatures up to 600 °C, with the objective of preserving the crystallinity and promoting Ge diffusion into nanoclusters. RBS shows that the Ge profile is more extended in depth for the sample implanted at 600 °C, compared to a room temperature implantation. As the energy of the ions is the same in both samples, this indicates that Ge is able to diffuse in depth during the implantation at 600 °C compared to implantation at ambient temperature. However, RBS/C shows that the minimal yield is higher for the implantation at 600 °C, indicating a high concentration of interstitials or that crystallinity is deteriorated, as confirmed by TEM.

Defect free strain relaxation of microcrystals on mesoporous patterned silicon

A perfectly compliant substrate would allow the monolithic integration of high-quality semiconductor materials such as Ge and III-V on Silicon (Si) substrate, enabling novel functionalities on the well-established low-cost Si technology platform. Here, we demonstrate a compliant Si substrate allowing defect-free epitaxial growth of lattice mismatched materials. The method is based on the deep patterning of the Si substrate to form micrometer-scale pillars and subsequent electrochemical porosification. The investigation of the epitaxial Ge crystalline quality by X-ray diffraction, transmission electron microscopy and etch-pits counting demonstrates the full elastic relaxation of defect-free microcrystals. The achievement of dislocation free heteroepitaxy relies on the interplay between elastic deformation of the porous micropillars, set under stress by the lattice mismatch between Ge and Si, and on the diffusion of Ge into the mesoporous patterned substrate attenuating the mismatch strain at the Ge/Si interface.

Stress Relaxation in SGOI Structure Obtained by Condensation

The development of effective buffer layer has required years of work in order to obtain relaxed SiGe substrates [1]. However, main drawback of this approach relies on the presence of embedded and numerous dislocations which can be detrimental for optimal applications. Recently, a surprising relaxation phenomenon has been observed on specific Silicon-Germanium On Insulator (SGOI) structures [4-5].It has been observed that when the sample is heated, slippage is observed at the SGOI/Buried Oxide (BOX) interface.The phenomenon is not clearly understood. However, several explanations have been raised. It can be explained by the mechanical properties by Ge-O bonds which are weaker than the Si-O bonds at the SGOI/BOX interface causing the slip. [2] Also, the Ge atoms in the last crystalline layer at the BOX interface decreases the quantity of Si atoms inducing less bonds between the Si atoms of SGOI and the BOX.We suggest to take advantage of this phenomenon to obtain fully relaxed SGOI layers without dislocations. This new approach would allow to create high performance relaxed SGOI layers in industrial conditions with 300 mm wafers. This innovation is relevant for several applications, such as optical applications and the formation of base substrate to generate tensile Si epitaxy layer. It has to be noticed that any Ge concentration until pure GeOI structure is possible.Figure 1 shows the different process steps to obtain relaxed SGOI layer explained below. SiGe epitaxy (fig.1-a) is performed on an 300mm SOI wafer by Rapid Thermal Chemical Vapor Deposition (RT-CVD). Germane (GeH4) and Dichlorosilane (DCS) are used as precursor gases to obtain a 20nm thick fully strained Si0.8Ge0.2 layer. Upstream work is performed to improve the uniformity of the SiGe layer (thickness and composition) within the 300mm wafer. Indeed, they are key parameters impacting Ge concentration within wafer uniformity obtained after condensation.[3]Then, condensation is performed (fig.1-b) using thermal oxidation in a 300mm industrial furnace under N2/O2 atmosphere at 1000°C during several hours. Condensation is tuned to obtain the desired Ge concentration in the SGOI structure. Condensation allows to transform a SiGe/Si/BOX structure into SiGe/BOX structure called SGOI. Two mechanisms are involved in the condensation. The first mechanism is the Si-selective oxidation in the SiGe layer allowing Ge atoms to accumulate at the oxidation interface. The second mechanism is the Ge diffusion in the structure which allows SiGe inter-diffusion. The Ge atoms are maintained and homogenized in depth of the SGOI layer during the interdiffusion mechanism thanks to the BOX acting as a diffusion barrier. [2]During this work, the layer composition, the thickness as well as the stress were characterized by ellipsometry, XRR, XRD and SIMS. In addition, the surface was analyzed by AFM to detect any crystal defects.In this study, we propose to investigate the relaxation of SGOI layer with a concentration of Ge=50% because such structure shows no defects after condensation [2]. Thereafter, it will be possible to carry out GeOI in the future.Figure 2 shows SiGe thickness and density measurement by XRR. A thickness variation of 13.67 A and a density variation of 0.22g/cm3 of the SGOI layer after condensation on the whole wafer is obtained. The average density is 4,31g/cm3 with a concentration of %Ge=51% which was our target concentration.Then, the relaxation phenomenon is studied using anneals in the temperature range [700;900] °C during several hours. Indeed, we chose a temperature close to the SiO2 viscosity temperature and a long annealing time allowing to generate a slow slip thus limiting defects.Figure 3 shows a RSM map obtained by XRD of an Si0.5Ge0.5OI layer after annealing at 800°C for 2h. The mapping shows Si substrate as well as the layer relaxed along the (113) and (224) planes at an angle Φ=45°. RSM map allows to calculate the relaxation rate which is 22%. The relaxation on the sample is a success that remains to be improved by annealing time or temperatures to be optimized.This new approach would allow the realization a defect free relaxed SGOI layer under industrial conditions on a 300mm wafer. It would provide a new method for applications such as optical or the growth of tensile Si channels.[1] P.M.Mooney, Materials Science and Engineering, 1996[2] F.Roze. PhD thesis, 2018[3] D.Valenducq, PhD thesis, 2021[4] V.Boureau et al., ECS, 2018[5] Usuda, Koji, et al., Solid-State Electronics, 2013 Figure 1

Fabrication of Oxide-Based All-Solid-State Batteries by a Sintering Process Based on Function Sharing of Solid Electrolytes.

Garnet-type Li7La3Zr2O12 (LLZ) has advantages of stability with Li metal and high Li+ ionic conductivity, achieving 1 × 10-3 S cm-1, but it is prone to react with electrode active materials during the sintering process. LISICON-type Li3.5Ge0.5V0.5O4 (LGVO) has the advantage of less reactivity with the electrode active material during the sintering process, but its ionic conductivity is on the order of 10-5 S cm-1. In this study, these two solid electrolytes are combined as a multilayer solid electrolyte sheet, where 2 μm thick LGVO films are coated on LLZ sheets to utilize the advantages of these two solid electrolytes. These two solid electrolytes adhere well through Ge diffusion without significant interfacial resistance. The LLZ-LGVO multilayer is combined with a LiCoO2 positive electrode and a lithium metal anode through annealing at 700 °C. The resultant all-solid-state battery can undergo repeated charge-discharge reactions for over 100 cycles at 25 or 60 °C. The LGVO coating suppresses the increases in the resistance from the solid electrolyte and interfacial resistance induced by annealing by ca. 1/40. As with sulfide-based all-solid-state batteries, function sharing of solid electrolytes will be a promising method for developing advanced oxide-based all-solid-state batteries through a sintering process.

Grain Size Engineering Using Amorphous-Ge/Si Stack to Enhance Channel Mobility for NAND Flash Memory

We demonstrated that polycrystalline-Si (poly-Si) channel mobility could be significantly enhanced through a combined effect of grain size engineering and Ge diffusion into the poly-Si channel. By crystallizing an amorphous-Ge/Si stack via thermal annealing, grain size enlargement and Ge diffusion occur together, resulting in an increase of the channel mobility of up to lpzrptsim100%. The enhanced poly-Si channel mobility improved the program and erase speeds by 55.8% and 30.5%, respectively, with no adverse effect on retention and endurance characteristics.

An experimental study of Ge diffusion through Ge2Sb2Te5

Ge thermal diffusion is not only the phenomenon limiting the decomposition and crystallization of Ge-rich GeSbTe alloys but is also responsible for some of the failures of the phase change memory devices using them. However, Ge diffusion in the canonical Ge2Sb2Te5 (GST-225) or in Ge-rich GeSbTe (GGST) alloys has been little studied experimentally. For these reasons, we have designed and set up a series of experiments aimed at highlighting and studying this diffusion within the solid phase, under technologically relevant conditions. For that, dedicated GST/Ge/GST structures have been grown at purpose, and the redistribution of Ge in GST-225 layers during isothermal and isochronal annealing has been studied using scanning and transmission electron microscopy based techniques. While Ge diffusion in amorphous GST-225 is negligible at low temperatures (i.e., below 140 °C), it is fast in crystalline GST-225 above 220 °C and proceeds via the grain boundaries. During such annealing, Ge diffusion is only limited by the emission of Ge atoms from the solid source and by the density of the grain boundaries providing diffusion paths to Ge through the polycrystalline layer, which tends to decrease as a function of the annealing time as the GST grains coalesce. These results show that diffusion phenomena can be activated at moderate temperatures in GST alloys and can change the chemical composition and morphology of Ge/GST composite materials. This supports the hypothesis that Ge diffusion may be responsible for the observed resistance drift and loss of integrity of the Phase Change Memories based on Ge-rich GeSbTe alloys in the SET state.

Diffusion coefficients and atomic mobilities in fcc Ag–Ge and Cu–Ge alloys: Experiment and modeling

The comprehensive investigations regarding the diffusion behaviors for Ag–Ge and Cu–Ge solders play key roles in their design and application. However, the diffusion behaviors in fcc Ag–Ge and Cu–Ge binary systems have not been carried out. To fill this gap, their diffusion characteristics were studied in this work based on the measured composition profiles of diffusion couples prepared for fcc Ag/Ag–Ge diffusion couples annealed at 873, 923 and 973 K as well as fcc Cu/Cu–Ge diffusion couples annealed at 1023, 1073 and 1123 K. On the basis of measured composition profiles, the composition-dependent interdiffusivities were calculated by the numerical inverse method incorporated in CALTPP (CALculation of ThermoPhysical Properties) program, which agree well with the ones calculated by the classic Sauer-Freise method. Besides, the atomic mobilities in fcc Ag–Ge and Cu–Ge alloys were assessed based on the diffusivities obtained from the literature and this work. Comparisons between model-predicted diffusion characteristics (viz. composition profiles and interdiffusivities) and experimental ones further validate the reliability of the presently obtained atomic mobilities. Insights gained in this work are of scientific significance and practical benefit for designing new Ge-bearing Ag and Cu solers.

Microscopic Views of Ge Segregation and Scavenging Ge on Thin Si on Epi-Ge(001)

Si capping layer is the most notable approach used in Ge metal-oxide-semiconductor (MOS);1-2 however, the Ge segregation and diffusion occurred during the growth of Si.3-4 The formation of undesirable GeOx is detrimental to the Ge nMOS reliability.5 This work focuses on using the scavenging process to reduce the segregated Ge atoms and to completely remove GeOx in the high-k/epi-Si/epi-Ge(001). We used high-resolution synchrotron radiation photoelectron spectroscopy (SRPES) to show the detailed development of Ge segregation and scavenging Ge using in-situ film growth, oxidation, and annealing. The Si films in 8Å thickness were grown on the epi-Ge(001) in a semiconductor molecular beam epitaxy (MBE) chamber.2 These samples were in-situ transferred to National Synchrotron Radiation Research Center in Taiwan for electronic structure studies using photoemission. Molecular oxygen was exposed to the epi-Si/epi-Ge(001) surfaces at 300°C in the photoemission chamber. The samples were then in-situ annealed at 500°C for 5 min under an ultra-high vacuum (UHV).The topmost surface of epi-Ge(001) is terminated with Ge-Ge buckled dimers.6 In the case of room-temperature grown amorphous Si (a-Si) film, the intensity of the Ge down-dimer component from the underlying epi-Ge remains as it is. The Ge up-dimer atoms were partly diffused into the a-Si film, and some of them were segregated to the top of the a-Si surface. The epi-Si grown at 260 - 280°C causes the rest of the Ge down-dimer atoms to move to the epi-Si surface to become both segregated Ge (segGe) and diffused Ge (diff-Ge). The growth of Si merely affects the topmost surface, and the Ge atoms in the second layer of the epi-Ge remain intact. A comparison of the amount of GeOx for HfO2/epi-Si/epi-Ge(001) and HfO2/epi-Ge(001) shows that the epi-Si has greatly reduced the amount of GeOx. However, the GeOx, segGe and diff-Ge components are still observed in the HfO2/epi-Si/Ge(001) samples.We have previously reported that three-time scavenging cycles have greatly reduced the amount of segGe and diff-Ge atoms in high-κ/epi-Si/n-Ge(001), thus decreasing electron traps.7 Each scavenging cycle includes room-temperature oxidation followed by thermal annealing. In this study, the oxidation of the as-grown epi-Si/epi-Ge(001) samples was performed at 300°C. It is worth noting that there is no GeOx formation on the surface after the thermal oxidation, which is different from the room-temperature oxidation of the epi-Si/epi-Ge(001) surfaces. In addition, the oxidation at 300°C affects part of the diff-Ge atoms to evaporate from the surface, which is also different from our previous work, where the diff-Ge component shows no change in intensity since the oxidation occurred at room temperature. The subsequent in-situ annealing at 500°C moved the residual Ge-boned Si (diff-Ge) inside the epi-Si to the surface to become part of the segGe atoms. In conclusion, we have used the aforementioned process to further reduce the segregated Ge, and thus the GeOx, on top of the epi-Si/epi-Ge(001).To whom the correspondence is addressed: mhong@phys.ntu.edu.tw (M. Hong), raynien@phys.nthu.edu.tw (J. Kwo), and pi@nsrrc.org.tw (T. W. Pi)AcknowledgmentsThis work is supported by MOST 110-2112-M-002-036-, 110-2622-8-002-014-, 110-2923-M-002-001-, and 110-2112-M-213-012- of the Ministry of Science and Technology in Taiwan.Reference 1 H. Arimura, E. Capogreco, A. Vohra, C. Porret, R. Loo, E. Rosseel, A. Hikavyy, D. Cott, G. Boccardi, L. Witters, G. Eneman, J. Mitard, N. Collaert, and N. Horiguchi, IEEE Int. Electron Devices Meet., 2.1.1−2.1.4 (2020). 2 H. W. Wan, Y. J. Hong, Y. T. Cheng, C. K. Cheng, C. H. Hsu, C. T. Wu, T. W. Pi, J. Kwo, and M. Hong, M., ACS Appl. Electron. Mater. 3, 2164−2169 (2021). 3 R. Loo, H. Arimura, D. Cott, L. Witters, G. Pourtois, A. Schulze, B. Douhard, W. Vanherle, G. Eneman, O. Richard, P. Favia, J. Mitard, D. Mocuta, R. Langer, N. Collaert, ECS J. Solid State Sci. Technol. 7, 66−72 (2018). 4 Y. T. Cheng, H. W. Wan, C. K. Cheng, C. P. Cheng, J. Kwo, M. Hong, T. W. Pi, Appl. Phys. Express 13, 085504 (2020). 5 J. Franco, B. Kaczer, P. J. Roussel, J. Mitard, S. Sioncke, L. Witters, H. Mertens, T. Grasser, G. Groeseneken, IEEE Int. Electron Devices Meet., 15.2.1−15.2.4 (2013). 6 Y. T. Cheng, Y. H. Lin, W. S. Chen, K. Y. Lin, H. W. Wan, C. P. Cheng, H. H. Cheng, J. Kwo, M. Hong, T. W. Pi, Appl. Phys. Express 10, 075701 (2017). 7 Y. T. Cheng, H. W. Wan, T. Y. Chu, T. W. Pi, J. Kwo, M. Hong, ACS Appl. Electron. Mater. 3, 4484-4489 (2021).

The Diffusion Mechanism of Ge During Oxidation of Si/SiGe Nanofins.

A recently discovered, enhanced Ge diffusion mechanism along the oxidizing interface of Si/SiGe nanostructures has enabled the formation of single-crystal Si nanowires and quantum dots embedded in a defect-free, single-crystal SiGe matrix. Here, we report oxidation studies of Si/SiGe nanofins aimed at gaining a better understanding of this novel diffusion mechanism. A superlattice of alternating Si/Si0.7Ge0.3 layers was grown and patterned into fins. After oxidation of the fins, the rate of Ge diffusion down the Si/SiO2 interface was measured through the analysis of HAADF-STEM images. The activation energy for the diffusion of Ge down the sidewall was found to be 1.1 eV, which is less than one-quarter of the activation energy previously reported for Ge diffusion in bulk Si. Through a combination of experiments and DFT calculations, we propose that the redistribution of Ge occurs by diffusion along the Si/SiO2 interface followed by a reintroduction into substitutional positions in the crystalline Si.

Effect of off-stoichiometric composition on half-metallic character of Co2Fe(Ga,Ge) investigated using saturation magnetization and giant magnetoresistance effect

We investigated the Ge-composition (γ) dependence of the saturation magnetization of Co2Fe(Ga, Ge) (CFGG) thin films and the magnetoresistance (MR) ratio of CFGG-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices together with first-principles calculations of the electronic states of CFGG. Theoretical calculations showed that spin polarization is highest at the stoichiometric composition γ = 0.56 in Co2Fe1.03Ga0.41Ge γ and that it decreases in off-stoichiometric CFGG, mainly due to the formation of CoFe antisites for Ge-deficient compositions and FeCo antisites for Ge-rich compositions, where CoFe (FeCo) indicates that Co (Fe) atoms replace the Fe (Co) sites. The saturation magnetic moment (μ s) per formula unit decreased monotonically as γ increased from 0.24 to 1.54 in Co2Fe1.03Ga0.41Ge γ . The μ s was closest to the Slater–Pauling value predicted for half-metallic CFGG at the stoichiometric composition γ = 0.56, indicating that stoichiometric CFGG has a half-metallic nature. This is consistent with the result for the theoretical spin polarization. In contrast, the MR ratio of CFGG-based CPP-GMR devices increased monotonically as γ increased from 0.24 to 1.10 and reached an MR ratio of 87.9% at the Ge-rich composition γ = 1.10. Then, the MR ratio decreased rapidly as γ increased from 1.10 to 1.48. Possible origins for the slight difference between the Ge composition at which the highest MR ratio was obtained (γ = 1.10) and that at which the highest spin polarization was obtained (γ = 0.56) are improved atomic arrangements in a Ge-rich CFGG film and the reduction of effective Ge composition due to Ge diffusion in the GMR stacks.

Size- and position-controlled Ge nanocrystals separated by high-k dielectrics

Germanium nanocrystals embedded in high-k dielectric matrices are of main interest for infrared sensing application, as a role model for Ge-based nanoelectronics passivation or for nonvolatile memory devices. The capability of the size control of those nanocrystals via rapid thermal processing of superlattice structures is shown for the [Ge–TaZrOx/TaZrOx]n, [Ge–TaZrOx/SiO2/TaZrOx]6, and [TaZrOx/Ge–SiO2]n superlattice systems. All superlattices were deposited by radiofrequency magnetron sputtering. Transmission electron microscopy (TEM) imaging confirms the formation of spherically shaped nanocrystals. Raman scattering proved the crystallization of Ge above 700°C. The TaZrOx crystallizes above 770°C, associated with a phase separation of Ta2O5 and ZrO2 as confirmed by x-ray diffraction. For the composite layers having 3 nm and 6 nm thickness, the size of the Ge nanocrystals correlates with the deposited layer thickness. Thicker composite layers (above 9 nm) form two fractions of nanocrystals with different sizes. An additional SiO2 layer in the [Ge–TaZrOx/SiO2/TaZrOx]6 superlattice stacks facilitates the formation of larger and better separated Ge nanocrystals. The deposition of Ge-SiO2 composite layers separated by pure TaZrOx illustrates the barrier effect of TaZrOx against Ge diffusion. All three material systems allow the controlled formation of Ge nanocrystals in amorphous matrices at temperatures above 700 and below 770°C.Graphical abstract