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Ge1−xSnx thin films with a Sn content of x ≥ 0.1 present a direct bandgap, which is very interesting for the fabrication of efficient photonic devices. The monostanogermanide phase, Ni(GeSn), is promising to form ohmic contact in GeSn-based Si photonic devices. However, the formation kinetics of Ni stanogermanides and the incorporation of Sn in Ni–GeSn phases are not fully understood. In this work, Ni thin films were deposited on Ge and Ge0.9Sn0.1 layers grown in epitaxy on an Si(100) substrate using magnetron sputtering technique. In situ x-ray diffraction measurements were performed during the solid-state reaction of Ni/Ge and Ni/Ge0.9Sn0.1. 1D finite difference simulations based on the linear parabolic model were performed to determine the kinetics parameters for phase growth. The nucleation and growth kinetics of Ni germanides are modified by the addition of Sn. A delay in the formation of Ni(GeSn) was observed and is probably due to the stress relaxation in the Ni-rich phase. In addition, the thermal stability of the Ni(GeSn) phase is highly affected by Sn segregation. A model was developed to determine the kinetic parameters of Sn segregation in Ni(GeSn). [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR), a pivotal process in hydrogen fuel cells crucial for enhancing fuel cell performance through suitable catalysts, remains a challenging aspect of development. This study explores the catalytic potential of germanene on Al (111), taking advantage of the successful preparation of stable reconstructed germanene layers on Al (111) and the excellent catalytic performance exhibited by germanium-based nanomaterials. Through first-principles calculations, we demonstrate that the O2 molecule can be effectively activated on both freestanding and supported germanene nanosheets, featuring kinetic barriers of 0.40 and 0.04 eV, respectively. The presence of the Al substrate not only significantly enhances the stability of the reconstructed germanene but also preserves its exceptional ORR catalytic performance. These theoretical findings offer crucial insights into the substrate-mediated modulation of germanene stability and catalytic efficiency, paving the way for the design of stable and efficient ORR catalysts for future applications. [ABSTRACT FROM AUTHOR]

Relaxed Si1−xGex layers on Si(001) serve as virtual substrates for strained Si or Ge layers. However, plastically relaxed layers inevitably contain misfit and threading dislocations, negatively affecting devices. Deposition of a SiGe layer on the backside of the substrate introduces a dislocation reservoir at the wafer edge that can reduce the threading dislocation density (TDD) of Si0.98Ge0.02/Si layers, as these preexisting dislocations start gliding toward the wafer center upon reaching the critical thickness. Here, we show that this low-strain system can be used effectively to study dislocation glide kinetics. In agreement with the literature, dislocation glide is a thermally activated process with an activation energy of 2.12–2.16 eV. Near the critical thickness, relaxation is sluggish and inefficient due to the linear dependence of the glide velocity on excess stress. At lower growth rates, dislocations from the edge reservoir are activated in a lower density due to the increase in the critical thickness through partial strain relaxation by already activated dislocations. Contrary to common models, here, the lowest possible growth rate is not essential for minimizing the TDD. Instead, a careful balance between low and high growth rates is beneficial. Overcoming the initial sluggish and inefficient relaxation phase is critical while also avoiding accumulation of strain energy, and, therefore, the activation of dislocation sources. Only in a later stage of buffer growth, the growth rate should be reduced to a minimum. With this method, the TDD of strain relaxed Si0.84Ge0.16 layers is reduced to 7 × 104 cm−2. [ABSTRACT FROM AUTHOR]

We performed Ge doping of α-Ga2O3 thin films grown on m-plane sapphire substrates using mist chemical vapor deposition. Although the typical growth rate was high at 4 μm/h, the resultant α-Ga2O3 thin films exhibited high crystallinity. We controlled the carrier density in the range of 8.2 × 1016–1.6 × 1019 cm−3 using bis[2-carboxyethylgermanium(IV)]sesquioxide as the Ge source. The highest mobility achieved was 66 cm2 V−1 s−1 at a carrier concentration of 6.3 × 1017 cm−3. Through secondary ion mass spectrometry analysis, a linear relationship between the Ge concentration in the α-Ga2O3 thin films and the molar ratio of Ge to Ga in the source solution was established. The quasi-vertical Schottky barrier diode fabricated using the Ge-doped α-Ga2O3 thin films exhibited an on-resistance of 7.6 mΩ cm2 and a rectification ratio of 1010. These results highlight the good performance of the fabricated device and the significant potential of Ge-doped α-Ga2O3 for power-device applications. [ABSTRACT FROM AUTHOR]

Two-dimensional germanium is considered a promising new channel material to replace silicon owing to its lower effective mass and larger electron–hole mobility. To investigate the transport characteristics of single-layer germanane transistors with gate lengths (Lg) below 5 nm, we utilize an ab initio quantum transport methodology. It was found that the n-type germanane transistors having Lg of 3 and 5 nm satisfy the International Technology Roadmap for Semiconductors (ITRS) requirements for the on-state current (Ion), effective delay time, and power-delay products of high-performance (HP) devices. Notably, by introducing a negative capacitive (NC) dielectric layer, the p-type germanane transistor having an Lg of 5 nm is almost able to meet the ITRS demands for HP devices. Despite reducing the gate length to 2 nm through the incorporation of the NC dielectric layer, the on-state currents for both n-type and p-type still satisfy approximately 80% of the ITRS standard. Therefore, monolayer germanane presents promising potential as a channel material in a sub-5 nm scale for HP applications. [ABSTRACT FROM AUTHOR]

This study explores the growth and structural characteristics of N d 2 O 3 layers on virtual germanium-rich SiGe substrates on Si(111). We focus on the emergence of the hexagonal phase depending on the stoichiometry of the virtual substrate. X-ray diffraction measurements reveal a hexagonal phase when N d 2 O 3 is grown directly on Si(111), while growth on Ge leads to a cubic oxide structure. On SiGe layers, the growth of the oxide results in a mixed phase containing hexagonal and cubic regions, regardless of the Ge content. The cubic structure grown on virtual Ge substrates exhibits strong tensile strain, while layers grown on SiGe layers show no strain. In situ growth control via electron diffraction shows a dependence of the oxide structure of the surface reconstruction of the virtual substrate. Growth on a 7 × 7 reconstruction leads to hexagonal parts on Si-based substrates, while growth on c (2 × 8) results in cubic oxide growth on Ge. Furthermore, oxide layers grown on virtual SiGe substrates form an interfacial silicate layer. The thickness of the interfacial layer is influenced by the Si content and the structure of the oxide layer enabling oxygen diffusion pathways. [ABSTRACT FROM AUTHOR]

By using first-principles calculations and micromagnetic simulations, we investigate the electronic structure, magnetic properties, and skyrmions in two-dimensional Janus Cr 2 XYTe 6 (X,Y = Si, Ge, Sn, X ≠ Y) monolayers. Our findings reveal that the Cr 2 XYTe 6 monolayers are ferromagnetic semiconductors with a high Curie temperature (T c). The bandgap and T c can be further increased by applying tensile strain. In addition, there is a transition from the ferromagnetic to the antiferromagnetic state at a compressive strain. Both Cr 2 SiSnTe 6 and Cr 2 SiGeTe 6 exhibit a large magnetic anisotropy energy, which are mainly associated with the significant spin–orbit coupling of the nonmagnetic Te atoms rather than that of the magnetic Cr atoms. Interestingly, the Cr 2 SiSnTe 6 monolayer exhibits a significant Dzyaloshinskii–Moriya interaction of 1.12 meV, which facilitates the formation of chiral domain walls and skyrmions. Furthermore, under tensile strain, chiral DWs can be transformed into skyrmions if applying an external magnetic field. These findings suggest that Janus Cr 2 XYTe 6 monolayers hold promise for spintronic nanodevice applications. [ABSTRACT FROM AUTHOR]

We demonstrate modulation of insulator metal transition (IMT) of VO2 films grown on single crystalline substrates through the effect of in-plane compression with crystallization of capping chalcogenide layer on the targeted VO2 films. Chalcogenide germanium–antimony–telluride (Ge2Sb2Te5: GST), which shows large volume reduction of 6.8% with its phase change from amorphous to crystal, was deposited on VO2 films grown on Al2O3 (001) and TiO2 (001) substrates, where V–V atoms along the cR-axis in the tetragonal VO2 phase align parallel and perpendicular to the substrate surfaces, respectively. As a result, counter shifts in temperature-dependence of resistance characteristics, to lower and higher directions, were observed for VO2 films on Al2O3 (001) and TiO2 (001), consistent with the lattice modulation of VO2 films by the in-plane compression introduced by GST crystallization. The obtained results open a way to realize large resistance change of IMT under constant temperature by controlling GST phases. [ABSTRACT FROM AUTHOR]

Radio Frequency (RF) sputtered germanium (Ge) thin films were deposited on glass substrate at in situ annealing temperatures of 400, 450, 500, 550, and 600 °C. X‐ray diffraction (XRD) and Raman spectroscopy revealed that the Ge films were initially amorphous but transformed to polycrystalline after annealing at 450 °C. Further annealing up to 600 °C resulted in improved crystallinity. Strain studies of the films using XRD and Raman showed compressive (out‐of‐plane) and tensile (in‐plane) strains, respectively, throughout all the annealing temperatures. The surface morphology of the films was recorded using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), which showed grain growth with annealing temperatures. The optical energy gap evaluated from absorption spectra for crystalline films decreased with annealing temperature, indicating improvement in crystallinity of films. The resistivity of the films deduced using current‐voltage measurements was found to decrease with annealing temperature, which can be attributed to enhancement in grain size. This study establishes a correlation between strain, grain size, optical energy gap, and electrical resistivity with temperature for Ge films deposited on glass substrates. Thus, the present study provides insights into variation in physical and electrical properties of films with in situ annealing temperature for their applicability in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Harnessing confined light on a subwavelength scale within Fano metasurfaces enhances light‐matter interaction on a flexible, low‐loss substrate. This approach enables the integration of ultra‐thin semiconducting films for designing low‐power, ultrafast switchable terahertz, and optical meta devices. Here, an ultra‐thin, ∼λ/6000 germanium overlayers of 25nm or 50nm is thermally evaporated onto a flexible Fano metallic metasurface to achieve ultrafast optical modulation of terahertz radiation. A remarkable 85% modulation depth with an ultrafast speed of 400 GHz is obtained in the resonant transmission. These ultrathin, flexible, and ultrafast functional metasurfaces pave the way for developing flexible terahertz active meta devices based on nanometric scale germanium films, offering the additional advantage of compatibility with complementary metal‐oxide‐semiconductor (CMOS) technology in microelectronics. [ABSTRACT FROM AUTHOR]

The phase transition temperature and crystallization kinetics of phase-change materials (PCMs) are crucial characteristics for their performance, data retention, and reliability in memory devices. Herein, the crystallization behavior and kinetics of a compositionally optimized, N-doped Ge-rich Ge–Sb–Te alloy (GGST) in the slow crystallization regime are systematically investigated using synchrotron x-ray diffraction (XRD) in situ during heat treatment. Uniform thin films (50, 25, 10, and 5 nm) of initially amorphous N-doped GGST are investigated. The specimens were heated up to 450 °C at a rate of 2 °C/min to estimate crystallization onsets by quantifiying the crystallized quantity during material transformation from the XRD patterns. Subsequent isothermal anneals have been performed to assess crystallization behavior and activation energies. Nucleation-controlled crystallization that progresses in two steps is observed, together with the emergence of Ge preceding cubic Ge2Sb2Te5, with a mild dependence of crystallization temperature on film thickness that is inverse to what has been observed in other systems. Ge and GST crystallization may be described occurring in three-time stages: (i) an incubation period; (ii) a fast growth period; and (iii) a very slow-growth period. Very high activation energies (between 3.5 and 4.3 eV) for each phase are found for the incubation time t0. The activation energy for Ge in the fast growth regime is close to the one reported for the crystallization of pure Ge films. In the case of Ge, the incubation time is strongly thickness-dependent, which may have important consequences for the scaling of memories fabricated with this class of materials. [ABSTRACT FROM AUTHOR]

The realization of nanoscale devices largely depends on our ability to control and manipulate interfacial interactions and, thus, understanding of the mechanisms of surface/interface instabilities. In this work, theoretically as well as technologically important and distinct two thermodynamic systems, which are exposed to (isobaric) and isolated from (isochoric) external body forces and surface tractions, are formulated by using irreversible thermodynamics in combination with the generalized variational method. The starting point for the present formulation closely follows up the Fowler and Guggenheim [Statistical Thermodynamics (University Press, Cambridge, 1952)] interpretation of the Planck inequality [Über Prinzip Vermehrung Entropie: Ann. Phys. Series 2(32), 462 (1887)] for isothermal reversible and irreversible (natural) infinitesimal changes in heterogeneous systems (multi-phase and multi-component). By combining this fundamental principle with the interlink between the dissipation function and global internal entropy production postulates, two distinct sets of governing equations for the surface drift-diffusion flux as well as the rate of evaporation/condensation and/or the growth/recrystallization of amorphous solid thin films are obtained for isochoric and isobaric systems. The role of Eshelby's energy-momentum tensor in the generalized potential for the interface displacement is found to differ (opposite in sign) for isochoric and isobaric systems. To demonstrate the importance of these sign conflicts, two sets of computer experiments are performed on isochoric and isobaric systems. They showed us that the elastic strain energy density contribution to the generalized driving force for surface drift-diffusion alone favoring flat and smooth surfaces in isobaric systems regardless of the sign of the uniaxial stress (healing), rather than causing the surface roughness and even catastrophic crack initiation as the case in internally strained isochoric systems. Computer simulations allowed us to track down the dynamical behavior of test modules by furnishing surface and strain energy variations, combined with the Global Helmholtz free change, which indicates the existence of two regimes: initial smooth surface undulations followed up by the rather chaotic crack formation and propagation stage at the middle of the thin film supported by the stiff substrate. In this study, we mainly focused on the development kinetics of "Stranski–Krastanow" island-type morphology, initiated by the nucleation route rather than the surface roughening scheme. The physicomathematical model, which is based on the irreversible thermodynamics treatment of surfaces and interfaces with singularities [T. O. Ogurtani, J. Chem. Phys. 124, 144706 (2006)], furnishes us to have autocontrol on otherwise free-motion of the triple junction contour line between the substrate and the droplet without presuming any equilibrium dihedral contact (wetting) angles at edges. We have also demonstrated the formation of the Stranski–Krastanow (SK)-type doublet islanding (quantum dots) as a stationary nonequilibrium state in an epitaxially strained thin flat droplet on a rigid substrate by introducing the wetting potential—invoked by the quantum confinement—into the scenario and carefully selecting the system parameters (size and shape) for the isochoric system represented by [Ge/Si (100)]. It has been also shown that on the contrary to common perceptions, the Stranski–Krastanow islands are in genuine stationary nonequilibrium states in the sense of Prigogine if one invokes proper free-moving boundary conditions at triple junctions deduced from the irreversible thermodynamics rather than ad hoc periodic or reflecting constrains at the edges. [ABSTRACT FROM AUTHOR]

On-chip integrated photonics with operating wavelength at short-wave infrared region is becoming popular for its potential advantages in extending the telecommunication bandwidth and the application in gas sensing. As an important component of integrated optoelectronic chips, high-performance waveguides have attracted widespread attention. In this work, high-performance Ge waveguides were designed and fabricated on the Ge-on-Si platform, in which germanium films were epitaxially grown by the chemical vapor deposition process. The propagation loss for the waveguide was measured to be 2.34 dB/cm at the wavelength of 2 μm through the cut-back method. The quantitative relationship between the waveguide propagation loss and sidewall roughness as well as material defect density was established by introducing an empirical coefficient m. The m value was calculated to be 3.8 × 10−4 dB for the waveguide with a fixed Ge thickness of 1.5 μm by fitting the experimental propagation loss data at an operating wavelength of 2 μm. This formula provides a significant reference for future design of waveguide dimension structures, where defect induced absorption loss is non-negligible. [ABSTRACT FROM AUTHOR]

We investigated the mechanism and kinetics of the formation of metastable BiGe solid phases during the amorphous-to-crystalline transformation of Ge films in contact with Bi. Ge/Bi/Ge sandwich films with a Bi film between amorphous Ge films, which were fabricated by sequential deposition of the components in a vacuum, were used in this study. The total thickness and composition of the sandwich films varied in the range from 30 to 400 nm and from 22 to 48 wt% Bi, respectively. Electron diffraction, high-resolution (S)TEM imaging, EDX, and EEL spectroscopy were used for in situ and ex situ characterization of the morphology, composition, and structure of Ge/Bi/Ge films in the temperature range of 20–271 °C. We proved the formation of polycrystalline Ge films containing up to 28 wt% Bi during low-temperature treatment. The interaction process was activated at ≈150 °C, resulting in the crystallization of Ge with the simultaneous formation of a quasi-homogeneous supersaturated solid solution throughout the entire volume of the film at ≈210 °C. We showed that the formation of crystalline Ge films with an extended solid solubility of Bi depended mostly on the overall composition of the tri-layer film. The role of metal-induced crystallization of the amorphous germanium in the formation of the supersaturated solid phases is discussed. [ABSTRACT FROM AUTHOR]

Strain imaging is a critical aspect in the design and characterization of opto-electronics, microelectronics, flexible electronics, and on-chip photonics. However, strain mapping techniques are often material specific and strain measurements in amorphous materials remain a challenge. Here, we demonstrate strain mapping and optical characterization of an amorphous semiconductor using scanning reflectance anisotropy microscopy. Using reflection anisotropy spectroscopy and finite element simulations on evaporated amorphous germanium films, we showcase the strain sensitivity of the ellipsometric parameters. We demonstrate nondestructive mapping for simple and complex strain states in amorphous systems. The sub-degree phase and amplitude sensitivity of the microscope is able to determine strain states on the order of 10 − 3 . [ABSTRACT FROM AUTHOR]

α-Sn, generally known as gray tin, has attracted significant scientific interest due to its potential to host novel topological phases. Studying the transport properties of α-Sn thin films grown on the InSb substrate has been challenging, as the InSb substrate also significantly contributes to the transport properties. In this article, we report a novel approach to epitaxially grow α-Sn thin films on an InSb substrate with a resistive buffer layer of CdTe. Thin films of α−Sn1−xGex (x = 0, 0.025) alloy of 15 nm thickness have been grown using molecular beam epitaxy. The high quality of the samples has been determined through high-resolution x-ray diffraction. The CdTe buffer layer has high resistance and acts as an insulating virtual substrate, which significantly suppresses contribution from InSb. Magnetotransport measurements show clear Shubnikov–de Hass oscillations in α−Sn1−xGex (x = 0, 0.025) thin films. A change in oscillation frequency is observed upon alloying with Ge, implying a modification in the electronic structure and demonstrating the effectiveness of the CdTe buffer layer approach. This work provides a new approach that enables the electronic transport characterization of the α−Sn1−xGex alloy system, which enables the study of the topological quantum states using electronic transport and their device applications. [ABSTRACT FROM AUTHOR]

We electrically characterized melt-quenched amorphized Ge2Sb2Te5 (GST) phase-change memory cells of 20 nm thickness, ∼66–124 nm width, and ∼100–600 nm length with and without photoexcitation in the 80–275 K temperature range. The cells show distinctly different current–voltage characteristics in the low-field (≲19 MV/m), with a clear response to optical excitation by red light, and high-field (≳19 MV/m) regimes, with a very weak response to optical excitation. The reduction in carrier activation energy with photoexcitation in the low-field regime increases from ∼10 meV at 80 K to ∼50 meV at 150 K (highest sensitivity) and decreases again to 5 meV at 275 K. The heterojunctions at the amorphous–crystalline GST interfaces at the two sides of the amorphous region lead to formation of a potential well for holes and a potential barrier for electrons with activation energies in the order of 0.7 eV at room temperature. The alignment of the steady state energy bands suggests the formation of tunnel junctions at the interfaces for electrons and an overall electronic conduction by electrons. When photoexcited, the photo-generated holes are expected to be stored in the amorphous region, leading to positive charging of the amorphous region, reducing the barrier for electrons at the junctions and hence the device resistance in the low-field regime. Holes accumulated in the amorphous region are drained under a high electric field. Hence, the potential barrier cannot be modulated by photogenerated holes, and the photo-response is significantly reduced. These results support the electronic origin of resistance drift in amorphous GST. [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication of ZnO thin films doped with Ge via the ALD method. With an optimized amount of Ge doping, there was an improvement in the conductivity of the films owing to an increase in the carrier concentration. The optical properties of the films doped with Ge show improved transmittance and reduced reflectance, making them more attractive for opto-electronic applications. The band gap of the films exhibits a blue shift with Ge doping due to the Burstein–Moss effect. The variations in the band gap and the work function of ZnO depend strongly on the carrier density of the films. From the surface studies carried out using XPS, we could confirm that Ge replaces some of the Zn in the wurtzite structure. In the films containing Ge, the concentration of oxygen vacancies is also high, which is somehow related to the poor electrical properties of the films at higher Ge concentrations. [ABSTRACT FROM AUTHOR]

The conditions for the growth of polycrystalline GeSn films on SiO2/Si(001) substrates by hot wire chemical vapor deposition are determined for the first time. The effect of the introduction of Sn into the Ge lattice on the morphology, structure, and transport properties of films is studied. GeSn films obtained at 300 °C have a uniform surface with a roughness of less than 1.0 nm. It is shown that the introduction of 5% Sn allows, without the use of recrystallization annealing, to significantly increase the hole mobility of polycrystalline GeSn films from 20 to 60 cm2 V−1 × s−1. despite the small grain size of 35 nm. Such films are of great interest for creating thin‐film transistors for active matrices' liquid crystal displays. [ABSTRACT FROM AUTHOR]

Epitaxial growth of BaSi2 films on Si(111) has demonstrated that the BaSi2 template can serve as a seed crystal for BaSi2 overlayers by molecular beam epitaxy (MBE) and shows high photoresponsivity, but not yet on Ge(111) substrates. We have investigated the effect of various templates on the photoresponsivity of BaSi2 films grown on Ge(111) substrates. Samples with MBE-grown templates exhibited high a-axis orientation, but the surface was uneven, leading to partial oxidation of the BaSi2 film. On the other hand, the sample without such templates showed a smoother surface but was confirmed to be polycrystalline. When a template formed by the combination of solid phase epitaxy (SPE) and subsequent annealing for 30 min was used, a-axis-oriented BaSi2 together with 111-oriented Si appeared in the θ–2θ x-ray diffraction (XRD) patterns. The fact that no crystalline Si was detected by the surface-sensitive Raman spectroscopy and that the full width at half maximum of the XRD BaSi2 600 peak was increased to 2.686° in such samples suggests that Si aggregates were at the BaSi2/Ge interface. The photoresponsivity of the epitaxial BaSi2 film with MBE-grown templates reached 0.14 A W−1 at a wavelength of 790 nm. This is the highest photoresponsivity reported so far for BaSi2 films on Ge substrates. Even for samples without the MBE-grown templates, SPE-grown templates significantly increased the photoresponsivity up to 0.10 A W−1. These results confirm that the template has a significant impact on the photoresponsivity of BaSi2 films on Ge(111) substrates. [ABSTRACT FROM AUTHOR]

Nano-engineering crystalline materials can be used to tailor their thermal properties. By adding new nanoscale phonon scattering centers and controlling their size, one can effectively decrease the phonon mean free path, hence the thermal conductivity of a fully crystalline material. In this Letter, we use the 3ω method in the temperature range of 100–300 K to experimentally report on the more than threefold reduction of the thermal conductivity of an epitaxially grown crystalline germanium thin film with embedded polydispersed crystalline Ge3Mn5 nano-inclusions with diameters ranging from 5 to 25 nm. A detailed analysis of the structure of the thin film coupled with Monte Carlo simulations of phonon transport highlights the role of the nano-inclusions volume fraction in the reduction of the phononic contribution to the thermal conductivity, in particular its temperature dependence, leading to a phonon mean free path that is set by geometrical constraints. [ABSTRACT FROM AUTHOR]

Infrared (IR) detection is vital for various military and civilian applications. Recent research has highlighted the potential of two‐dimensional (2D) topological semimetals in IR detection due to their distinctive advantages, including van der Waals (vdW) stacking, gapless electronic structure, and Van Hove singularities in the electronic density of states. However, challenges such as large‐scale patterning, poor photoresponsivity, and high dark current of photodetectors based on 2D topological semimetals significantly impede their wider applications in low‐energy photon sensing. Here, we demonstrate the in situ fabrication of PtSe2/Ge Schottky junction by directly depositing 2D PtSe2 films with a vertical layer structure on a Ge substrate with an ultrathin AlOx layer. Due to high quality junction, the photodetector features a broadband response of up to 4.6 μm, along with a high specific detectivity of ~1012 Jones, and operates with remarkable stability in ambient conditions as well. Moreover, the highly integrated device arrays based on PtSe2/AlOx/Ge Schottky junction showcases excellent Mid‐IR (MIR) imaging capability at room temperature. These findings highlight the promising prospects of 2D topological semimetals for uncooled IR photodetection and imaging applications. [ABSTRACT FROM AUTHOR]

We report a change in the structural and magnetic properties of epitaxial Mn5Ge3 on a Ge-on-Si (111) substrate by applying strain engineering through ms-range flash lamp annealing (FLA). X-ray diffraction results demonstrate that during FLA for 20 ms, the formation of nonmagnetic MnxGey secondary phases is suppressed, while the in-plane expansion of the lattice increases with increasing annealing temperature. Temperature-dependent magnetization results indicate that the Curie temperature of Mn5Ge3 rises from 287 K in the as-prepared sample to above 400 K after FLA, making Mn5Ge3 an attractive material for spintronics. Experimental results together with theoretical Monte Carlo simulations allow us to conclude that the expansion of the in-plane lattice causes the increase of the Curie temperature due to enhancement of the ferromagnetic interaction between Mn atoms. [ABSTRACT FROM AUTHOR]

The chemical etching of germanium in Br2 environment at elevated temperatures is described by the Michaelis–Menten equation. The validity limit of Michaelis–Menten kinetics is subjected to the detailed analysis. The steady-state etching rate requires synergy of two different process parameters. High purity gas should be directed to the substrate on which intermediate reaction product does not accumulate. Theoretical calculations indicate that maximum etching rate is maintained when 99.89% of the germanium surface is covered by the reaction product, and 99.9999967% of the incident Br2 molecules are reflected from the substrate surface. Under these conditions, single GeBr2 molecule is formed after 30 million collisions of Br2 molecules with the germanium surface. [ABSTRACT FROM AUTHOR]

Planar tetracoordinate silicon, germanium, tin, and lead (ptSi/Ge/Sn/Pb) species are scarce and exotic. Here, we report a series of penta-atomic ptSi/Ge/Sn/Pb XB2Bi2 (X = Si, Ge, Sn, Pb) clusters with 20 valence electrons (VEs). Ternary XB2Bi2 (X = Si, Ge, Sn, Pb) clusters possess beautiful fan-shaped structures, with a Bi–B–B–Bi chain surrounding the central X core. The unbiased density functional theory (DFT) searches and high-level CCSD(T) calculations reveal that these ptSi/Ge/Sn/Pb species are the global minima on their potential energy surfaces. Born–Oppenheimer molecular dynamics (BOMD) simulations indicate that XB2Bi2 (X = Si, Ge, Sn, Pb) clusters are robust. Bonding analyses indicate that 20 VEs are perfect for the ptX XB2Bi2 (X = Si, Ge, Sn, Pb): two lone pairs of Bi atoms; one 5c–2e π, and three σ bonds (two Bi–X 2c–2e and one B–X–B 3c–2e bonds) between the ligands and X atom; three 2c–2e σ bonds and one delocalized 4c–2e π bond between the ligands. The ptSi/Ge/Sn/Pb XB2Bi2 (X = Si, Ge, Sn, Pb) clusters possess 2π/2σ double aromaticity, according to the (4n + 2) Hückel rule. [ABSTRACT FROM AUTHOR]

Herein, we report the transport properties of Ge films. The variable-range hopping transport at low temperatures (T ≲ 50 K) and thermal activation transport at high temperatures (T ≳ 50 K) are observed in our Ge films. In the different temperature regimes, the anomalous magnetotransport properties are observed. In the low-temperature regime (T ≲ 15 K) , the negative magnetoresistance (MR) at low field and positive MR at high field can be seen. In the moderate-temperature regime (15 K ≲ T ≲ 100 K) , the positive MR curve gradually evolves from a linear curve to a parabolic curve with increasing temperature, and the MR magnitude appears to be insensitive to temperature. In the high-temperature regime (T ≳ 100 K) , the positive MR value increases with increasing temperature. By considering the angular-dependent MR, we can determine that the negative MR comes from the spin-related mechanism, and the positive MR is caused by the orbital-related mechanism. However, further study is required to determine the exact mechanisms behind the anomalous magnetotransport properties. [ABSTRACT FROM AUTHOR]

The Ni-stanogermanides were formed via an interfacial reaction between Ni film and a Ge1−xSnx (x = 0.083) epilayer grown on a Si substrate driven by thermal treatment, and their microstructural and chemical features were investigated as a function of a rapid thermal annealing (RTA) temperature. The Ni3(Ge1−xSnx) phase was formed at the RTA temperature of 300 °C, above which Ni(Ge1−xSnx) was the only phase formed. The fairly uniform Ni(Ge1−xSnx) film was formed without unreactive Ni remaining after annealing at 400 °C. However, the Ni(Ge1−xSnx) film formed at 500 °C exhibited large surface and interface roughening, followed by the formation of Ni(Ge1−xSnx) islands eventually at 600 °C. The Sn concentration in Ni(Ge1−xSnx) gradually decreased with increasing RTA temperature, implying the enhancement of Sn out-diffusion from Ni(Ge1−xSnx) grains during the Ni-stanogermanidation process at higher temperature. The out-diffused Sn atoms were accumulated on the surface of Ni(Ge1−xSnx), which could be associated with the low melting temperature of Sn. On the other hand, the out-diffusion of Sn atoms from Ni(Ge1−xSnx) along its interface was dominant during the Ni/Ge1−xSnx interfacial reaction, which could be responsible for the segregation of metallic Sn grains that were spatially confined near the edge of Ni(Ge1−xSnx) islands. [ABSTRACT FROM AUTHOR]

Flexible information memory is the key component of flexible electronic devices and the core of intelligent wearable devices. In this paper, Ge/Sb multilayer phase change films of various thickness ratios were prepared using polyether ether ketone as substrate, and their flexible phase change properties and device conversion characteristics were studied. After bending for 100000 times and bending experiments with different bending radius, the film can still realize the transition from amorphous to crystalline states, and the resistance fluctuation was small. Bending, stretching and pressing of the film resulted in grain refinement and increasing of crystalline resistance. The flexible electronic devices using Ge/Sb multilayer films were prepared. The phase change memory device can realize reversible conversion between SET and RESET states with different pulse widths in flat, bent states and after bending many times. All findings show that Ge/Sb multilayer films on PEEK substrate have broad application prospects in high-performance flexible memory in the future. [ABSTRACT FROM AUTHOR]

We investigate the effects of oxygen on the thermal diffusion of germanium atoms, implanted inside a thermally grown SiO2 layer, during high temperature processes (1100 °C, 60 min). The impact of the presence of oxygen on Ge diffusion is studied as a function of its origin, as it can come either from the annealing atmosphere (extrinsic source) or from the SiO2 matrix itself (intrinsic source). 18O labeling of the oxygen either in the annealing atmosphere or in the silica substrate, together with an isotopically sensitive ion beam analysis, shows a clear oxygen-dependence in germanium diffusion. This is especially so when oxygen is present in the annealing atmosphere, where it is responsible for an enhancement of germanium out-diffusion and redistribution into several peaks during annealing, through the formation of GeO molecules. A new three-process model is proposed to explain the impact of a contaminated atmosphere on the Ge redistribution. This is notably shown that a third Ge peak arises at the sample surface when the annealing atmosphere is contaminated by oxygen. This peak formation is explained by the oxidation of Ge present at the vicinity of the surface by oxygen coming from the annealing atmosphere. This is also shown that O2 molecules can diffuse in depth, with a coefficient of diffusion D O 2 ∼ 10 − 9 c m 2 / s , until the densities of Ge and irradiation-induced defects increase, causing the progressive oxidation of Ge in depth and the restoration of the SiO2 stoichiometry. [ABSTRACT FROM AUTHOR]

Measurements of conductance fluctuations in undoped hydrogenated amorphous germanium (a-Ge:H) find power spectra that vary with inverse frequency (1/f) that are characterized by non-Gaussian statistics. The non-Gaussian aspect of the 1/f noise is reflected in (1) histograms of the noise power per octave that are described by lognormal distributions, (2) power-law second spectra, and (3) strong correlations of the noise power in frequency-space. In contrast, measurements of current fluctuations in polycrystalline germanium thin films find 1/f noise with Gaussian statistics. These results are discussed in terms of a model of filamentary conduction, where the filament structure and conductance in a-Ge:H are modulated by hydrogen motion. [ABSTRACT FROM AUTHOR]

The efficiency of thin film photoelectric devices can be improved by redirecting incident electromagnetic radiation along their surface layers. Redirection can be achieved using antireflection coatings made of subwavelength dielectric particle arrays. In this study, we fabricate such coatings, consisting of Ge particles on quartz glass substrates via solid-state dewetting, transforming thin Ge films into compact particles. Using optically transparent substrates, we measure reflection and transmission spectra and determine absorption spectra, showing that substrates coated with Ge particles absorb much more strongly than substrates coated with continuous Ge films. The spectra obtained using objective lenses with different aperture angles indicate that scattered radiation is predominantly directed at glancing angles to the substrate surface. The lateral propagation of scattered radiation is the result of destructive interference, which suppresses both reflected and transmitted radiation. [ABSTRACT FROM AUTHOR]

Amorphous germanium films on nonrefractory glass substrates were annealed by ultrashort near-infrared (1030 nm, 1.4 ps) and mid-infrared (1500 nm, 70 fs) laser pulses. Crystallization of germanium irradiated at a laser energy density (fluence) range from 25 to 400 mJ/cm2 under single-shot and multishot conditions was investigated using Raman spectroscopy. The dependence of the fraction of the crystalline phase on the fluence was obtained for picosecond and femtosecond laser annealing. The regimes of almost complete crystallization of germanium films over the entire thickness were obtained (from the analysis of Raman spectra with excitation of 785 nm laser). The possibility of scanning laser processing is shown, which can be used to create films of micro- and nanocrystalline germanium on flexible substrates. [ABSTRACT FROM AUTHOR]

Germanium films were grown on c-plane sapphire with a 10 nm AlAs buffer layer using molecular beam epitaxy. The effects of Ge film thickness on the surface morphology and crystal structure were investigated using ex situ characterization techniques. The nucleation of Ge proceeds by forming (111) oriented three-dimensional islands with two rotational twin domains about the growth axis. The boundaries between the twin grains are the origin of the 0.2% strain and tilt grains. The transition to a single-grain orientation reduces the strain and results in a better-quality Ge buffer. Understanding the role of thickness on material quality during the Ge(111)/Al2O3(0001) epitaxy is vital for achieving device quality when using group IV material on the sapphire platform. [ABSTRACT FROM AUTHOR]

Binary iron‐germanium phases are promising materials in magnetoelectric, spintronic or data storage applications due to their unique magnetic properties. Previous protocols for preparation of FexGey thin films and nanostructures typically involve harsh conditions and are challenging in terms of phase composition and homogeneity. Herein, we report the first example of single source chemical vapor deposition (CVD) of FexGey films. The appreciable volatility of [Ge[Fe2(CO)8]2], [Cl2GeFe(CO)4]2 and Me₂iPr₂NHC ⋅ GeCl2 ⋅ Fe(CO)4 allowed for their application as precursors under standard CVD conditions (Me₂iPr₂NHC=1,3‐diisopropoyl‐4,5‐dimethylimidazol‐2‐ylidene). The thermal decomposition products of the precursors were characterized by TGA and powder XRD. Deposition experiments in a cold‐wall CVD reactor resulted in dense films of FexGey. During the optimization of synthetic conditions for precursor preparation the new iron‐germanium cluster Cl2Ge[Fe2(CO)8]Ge[Fe2(CO)8] was obtained in experiments with a higher stoichiometric ratio of GeCl2 ⋅ 1,4‐dioxane vs. Fe2(CO)9. [ABSTRACT FROM AUTHOR]

The crystallization of sputter-deposited substrate-free films of amorphous germanium was induced by electron irradiation at SEM-level energies of less than 20 keV at ambient temperature using an electron probe microanalyzer. Instantaneous crystallization, referred to as explosive crystallization, occurred consistently at 2–20 keV; the threshold of electron fluxes is 1015–1016 m−2 s−1, which is five to six orders of magnitude lower than those at 100 keV reported previously. This process is expected to be advantageous in the production of polycrystalline Ge films since it is rapid, requires little energy, and results in negligible damage to the substrate. [ABSTRACT FROM AUTHOR]

Improving the thermal stability of Ni/GeSn intermetallics is of great importance to avoid surface degradation and Sn segregation. For this purpose, we studied the effects of pre-amorphization by ion implantation (PAI) of GeSn layers prior to metallization. The impact of Si, Ge, C, or Ge + C PAI was evaluated in terms of phase sequence, morpohological, and electrical evolution during the solid-state reaction. The overall phase sequence, followed by in situ x-ray diffraction, was comparable with or without PAI and went as follows: the Ni 5 (GeSn) 3 hexagonal phase was obtained first, followed by the mono-stanogermanide phase: Ni(GeSn). Nevertheless, the threshold temperature for phase formation varied. These variations, depending on the nature of the implanted ions, can be related to kinetic and/or thermodynamic factors as supported by the analysis of bibliography for silicides and germanides. Additionally, it was reported that the use of Si or Ge implantation did not significantly impacted the surface morphology of the layers. On the other hand, the implantation of C positively impacts the surface morphology evolution by delaying Sn long-range diffusion and Ni(GeSn) agglomeration. This trend was then highly beneficial for preserving electrical stability in an enhanced process window. [ABSTRACT FROM AUTHOR]

The heterogeneous epitaxial system of BaTiO3/Ge (BTO/Ge) is of great interest for both fundamental research and device applications, thanks to its quasi-lattice-matching feature and the integration of functional oxides on semiconductors. Currently, the heteroepitaxial growth of crystalline BTO films on Ge includes the utilization of ultrahigh vacuum tools and complex surface passivation pre-treatment as well as careful control of oxygen partial pressure during the growth. Meanwhile, oxygen vacancies in oxides strongly impact their structural and electrical properties. Here, we report a facile method to directly grow single crystalline BTO films on Ge using pulsed laser deposition. The strict control of oxygen partial pressure ensures a sharp interface with an atom-to-atom registry and also leads to the oxygen-deficient characteristics of BTO. The epitaxial relationship of BTO and Ge is [110] BTO (001)//[100] Ge (001). Detailed crystallographic studies on BTO films with different thicknesses show that, for the films with a thickness less than 20 nm, BTO shows a mixture of tetragonal and cubic phases due to the oxygen vacancies and the strain from the Ge substrate and the cubic phase eventually dominates as the film thickness increases. Such oxygen-deficient BTO films reveal conducting characteristics rather than dielectric properties. The oxygen vacancies can be partly "cured" after a low temperature annealing process. These results not only demonstrate the possibility to directly grow single crystalline oxides on semiconductors without surface passivation but also highlight the importance of oxygen vacancies and lattice strain on the crystallographic and electrical properties of BTO films. [ABSTRACT FROM AUTHOR]

Using vertical spin-valve devices, we experimentally investigate the room-temperature spin diffusion length in an undoped p -Ge layer grown on ferromagnetic Fe 3 Si. Because low-temperature molecular beam epitaxy techniques enable us to grow vertically stacked and all-epitaxial CoFe/Ge/Fe 3 Si trilayers on Si(111), we can intentionally vary the thickness (t Ge ) of the intermediate undoped p -Ge layer during the growth. With decreasing t Ge , the magnitude of the spin signals gradually increases at room temperature. From the analysis based on the model by Fert and Jaffrès, the room-temperature spin diffusion length in the undoped p -Ge grown on Fe 3 Si is experimentally estimated to be ∼ 8.4 nm, much shorter than those reported in previous works on commercial p -Ge substrates. [ABSTRACT FROM AUTHOR]

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs. [ABSTRACT FROM AUTHOR]

The thermal diffusion of Ge implanted into SiO2 films growth on a Si substrate has been studied by nuclear analyses and μ-Raman spectroscopy with and without the presence of co-implanted 30Si and 29Si barriers, each located from both sides of the Ge implanted distribution. Combination of Rutherford backscattering spectroscopy and Resonant nuclear reaction analysis shows that, under thermal activation at 1100°C, implanted Ge diffuses differently toward the sample surface and the SiO2/Si interface due to the occurrence of Ge outgassing effects, as well as the non-homogenous distributions of the implanted ion species and the defects they have generated inside SiO2. A maximum local atom concentration of co-implanted silicon as low as ∼1.6 at. % is found to completely block the germanium diffusion in both directions, leading to the formation of Ge nanocrystals and Si/Ge aggregates evidenced by μ-Raman spectroscopy. In addition to highlighting the role of Si excess on the Ge trapping mechanism, such a result makes the nominal silicon oxide stoichiometry and composition two crucial parameters to stabilize Ge during high temperature annealing, which explains the strong discrepancies reported for the Ge thermal diffusion coefficient in the literature. [ABSTRACT FROM AUTHOR]

Epitaxial Ge films were grown on Si(001) substrates by molecular beam epitaxy. During epitaxial growth, two carbon interlayers were deposited at varying substrate temperatures (140 − 620 ° C) and with varying C quantity (0 − 1.5 monolayers). The influence of the second carbon interlayer on in-plane strain was investigated using high-resolution x-ray diffraction and transmission electron microscopy (TEM). All samples exhibited compressive strain, which was attributed to substitutional incorporation of carbon atoms. In-plane strain decreases with increasing substrate temperature during carbon deposition, indicating that enhanced surface mobility of carbon adatoms leads to formation of carbon clusters. This was confirmed by cross-sectional TEM investigations. Variation of C quantity at 180 ° C reveals maximum strain at an intermediate quantity of 0.8 monolayers. Omission of the second C interlayer results in much lower strain, indicating a mismatch between the two Ge layers separated by a C interlayer. This could be used to enforce dislocation filtering following the principle of strained layer superlattices. An upper estimate of 1 × 10 − 3 was found for the mismatch strain, resulting in a critical thickness for dislocation filtering of h c = 153 nm. A sample just exceeding h c exhibited a clear dislocation reduction effect as shown by TEM. [ABSTRACT FROM AUTHOR]

The electrical characteristics and deep-level transient spectroscopy of a hybrid poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GeNCs/Si heterojunction with Ge nanoclusters grown by molecular beam epitaxy on a p-type Si(001) substrate are investigated. The heterostructure shows good rectifying J–V characteristics, the dark current exhibits an activation energies of 280 meV and 550 meV, while the reverse bias leakage current is suppressed due to the coating of Ge nanoclusters with PEDOT:PSS. We show that recombination via deep hole states close to grain boundaries can be partly suppressed by the PEDOT:PSS thin films, leading to a decrease in the saturation current and an improvement of the rectification without deterioration of forward current. [ABSTRACT FROM AUTHOR]

Sub-nanometer thickness accuracy and excellent conformity make atomic layer deposited films prevalent in modern electronics, continuously shrinking in size. The thermal resistance of these films plays a major role in the overall energy efficiency of miniaturized devices. We report very sensitive thermal conductivity measurements of amorphous Al 2 O 3 thin films grown using atomic layer deposition in the temperature range of 100–300 K. The 3 ω method is used to characterize these films ranging from 17.0 to 119.4 nm in thickness, using a series-resistor model to deconvolve the intrinsic thermal conductivity of the film from thermal boundary resistances inherently present in the multilayer system. The thermal conductivity of amorphous alumina films with a density of 2.77 ± 0.14 g cm − 3 is measured to be 1.73 ± 0.08 W m − 1 K − 1 at 300 K. Measurements were carried out on germanium and sapphire substrates, leading to no substrate dependence of the films' thermal conductivity, within experimental accuracy. On the other hand, thermal boundary resistances of the systems Pt/Al 2 O 3 /substrate are observed to be strongly substrate-dependent, with values ranging from 2.1 × 10 − 8 m 2 K W − 1 to 3.7 × 10 − 8 m 2 K W − 1 at 300 K for films deposited on sapphire and germanium, respectively. These results provide further insights into the significance of interfaces in thermal transport across layered materials, in particular, for potential germanium-based devices. [ABSTRACT FROM AUTHOR]

In this article, we employed the nanosecond Z-scan technique to demonstrate the nonlinear optical response in Ge30Se55Bi15 thin films after thermal and photoannealing. The intensity dependent open aperture Z-scan traces reveal that all the samples, i.e., as-prepared, thermal, and photoannealed thin films, exhibit reverse saturable absorption. The experimental results indicate that both thermal and photoannealing can be efficiently used to enhance the nonlinear absorption coefficient (β) compared to the as-prepared sample. We further demonstrate that the β value of thermally annealed and as-prepared samples increases significantly at higher intensities. On the contrary, the β value of the photoannealed sample does not exhibit appreciable changes against the intensity variation. [ABSTRACT FROM AUTHOR]

Various doping concentrations of boron (B)-doped germanium nanocrystal (Ge NC) films were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique followed by thermal annealing treatment. The electronic properties of B-doped Ge NCs films combined with the microstructural characterization were investigated. It is worthwhile mentioning that the Hall mobilities μ Hall of Ge NCs films were enhanced after B doping and reached to the maximum of 200 cm2 V−1, which could be ascribed to the reduction in surface defects states in the B-doped films. It is also important to highlight that the temperature-dependent mobilities μ H (T) exhibited different temperature dependence trends in the Ge NCs films before and after B doping. A comprehensive investigation was conducted to examine the distinct carrier transport properties in B-doped Ge NC films, and a detailed discussion was presented, focusing on the scattering mechanisms involved in the transport process. [ABSTRACT FROM AUTHOR]

Titanium dioxide is well known as a photoactive material to be activated under ultraviolet irradiation and is either employed as a photocatalyst or exhibits superhydrophilic behavior after reducing the surface energy under illumination for self-cleaning or anti-fogging surfaces. For increasing the reactivity of the thin films under solar illumination, a reduced band gap is desired. Doping with transition metals or with nitrogen has been reported in the literature. However, the incorporation of nitrogen into the growing film is a much more complex process, which is presently not completely understood. TiO2 thin layers were produced by ion beam sputter deposition, which should allow the usage of temperature-sensitive substrates. The deposition has been performed in the existing experimental setup, previously used for investigations on Ag and Ge thin film physical vapor deposition processes, where the influence of the sputtered and reflected particles and their accompanying energy flux on the grain size, surface morphology, and conductivity have been measured. By adjusting the geometry between the incident ion beam, the sputter target, and the substrate, independently from the primary ion energy and species, a controlled deposition of samples was possible. Conventional ion implantation was employed to implant either carbon or nitrogen ions below the surface for bandgap engineering. The resulting thin films have subsequently been investigated for optical properties, stoichiometry, structural properties, surface topography, and photoactivity. The aim was to find an optimized geometry and to determine the exact particle and energy flux necessary for these conditions. Thus, the process opens up for transfer or scaling when assuming future industrial applications. [ABSTRACT FROM AUTHOR]

Superconducting germanium films are an intriguing material for possible applications in fields such as cryogenic electronics and quantum bits. Recently, there has been a great deal of progress in hyperdoping of Ga doped Ge using ion implantation. Thin film growth of such a material would be advantageous, allowing homoepitaxy of doped and undoped Ge films and opening possibilities for vertical Josephson junctions. Here, we present our studies on the growth of one layer of hyperdoped superconducting germanium thin film via molecular beam epitaxy. We observe a fragile superconducting phase, which is extremely sensitive to processing conditions and can easily phase-segregate, forming a percolated network of pure gallium metal. By suppressing phase segregation through temperature control, we find a superconducting phase that is unique and appears coherent to the underlying Ge substrate. [ABSTRACT FROM AUTHOR]

In order to validate the flexible storage potential, [Ge 2 Sb 2 Te 5 (3 nm)/Sb(7 nm)] 5 superlattice-like phase change films on flexible polyetheretherketone substrates were prepared by magnetron sputtering. The phase transition behavior and the effect of different bending cycles on the properties were investigated. Compared with conventional rigid Si/SiO 2 substrate, [Ge 2 Sb 2 Te 5 (3 nm)/Sb(7 nm)] 5 films based on a flexible substrate possessed better thermal stability and surface adhesion. The superlattice-like structure was confirmed by transmission electron microscopy. PCM devices based on polyetheretherketone substrates were fabricated and the electrical conversion characteristics before and after bending were verified and compared. [ABSTRACT FROM AUTHOR]

A patterned Si substrate is used to reduce the threading dislocation density (TDD) in a Ge epitaxial film for near-infrared photonic device applications. Using photolithography and dry etching, an array of submicron-wide strips with a rectangular cross-section is patterned in the [110] direction of a Si (001) wafer. A Ge film as thick as 1 µm is grown on the patterned Si by chemical vapor deposition with an ordinary two-step growth method, where a buffer layer of pure Ge as thin as 50 nm is grown at a low temperature of 370°C, followed by growth at an elevated temperature of 700°C. A Ge film is formed with a reasonably flat surface despite the non-flat starting Si surface as well as the large lattice mismatch of 4.2% between Ge and Si. The etch-pit density measurements for the Ge film exhibits TDD of about 6 × 107 cm–2, which is significantly lower than that of about 2 × 108 cm–2 for the film on the unpatterned region prepared on the same Si substrate. The TDD reduction is attributed to a trapping of the dislocations in the trench regions between the Si strips, as observed in cross-sectional transmission electron microscope images. [ABSTRACT FROM AUTHOR]

The current work describes a novel method of growing thin films of stable crystalline ST12-Ge, a high pressure polymorph of Ge, on Si substrate by a nonequilibrium VLS technique. The study explores the scheme of band engineering of ST12-Ge by inducing process stress into it as a function of the growth temperature and film thickness. In the present work, ST12-Ge films are grown at 180–250 °C to obtain thicknesses of ~4.5–7.5 nm, which possess extremely good thermal stability up to a temperature of ~350 °C. Micro-Raman study shows the stress induced in such ST12-Ge films to be compressive in nature and vary in the range of ~0.5–7.5 GPa. The measured direct band gap is observed to vary within 0.688 eV to 0.711 eV for such stresses, and four indirect band gaps are obtained to be 0.583 eV, 0.614–0.628 eV, 0.622–0.63 eV and 0.623–0.632 eV, accordingly. The corresponding band structures for unstrained and strained ST12-Ge are calculated by performing DFT simulation, which shows that a compressive stress transforms the fundamental band gap at M-Γ valley from 'indirect' to 'direct' one. Henceforth, the possible route of strain-induced band engineering in ST12-Ge is explored by analyzing all the transitions in strained and unstrained band structures along with substantiation of the experimental results and theoretical calculations. The investigation shows that unstrained ST12-Ge is a natural n-type semiconductor which transforms into p-type upon incorporation of a compressive stress of ~5 GPa, with the in-plane electron effective mass components at M-Γ band edge to be ~0.09me. Therefore, such band engineered ST12-Ge exhibits superior mobility along with its thermal stability and compatibility with Si, which can have potential applications to develop high-speed MOS devices for advanced CMOS technology. [ABSTRACT FROM AUTHOR]