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Er-germanosilicide [Er(Si1− zGe z)2− y] films were formed on strained Si1− xGe x layers with different Ge contents ( x = 0.14 and 0.28), and their dependency of formation kinetics on the Ge concentrations was investigated while minimizing the oxygen-incorporation effect using a TaN capping layer. When a ~30 nm-thick Er film was used, uniform Er(Si1− zGe z)2− y films were obtained at an annealing temperature of around 600 °C without their agglomeration and also the strain relaxation of the remaining Si1− xGe x layer. The increase in the Ge concentration of the reacting Si1− xGe x layer enhanced the formation of the crystalline Er(Si1− zGe z)2− y film. Furthermore, some enrichment of the Ge content within the Er(Si1− zGe z)2− y film occurred in comparison with that in the initial and remaining Si1− xGe x layers. [ABSTRACT FROM AUTHOR]

The in-situ procedure is used to study the modification of thin (200-600 nm) germanium films induced by nanosecond pulses of a ruby laser. The films are produced using the ion-beam or magnetron sputtering on single-crystalline silicon (Si), sapphire (AlO), and fused silica (α-SiO) substrates. The results on the dynamics of the laser-induced processes are obtained using the optical probing of the irradiated region at wavelengths of λ = 0.53 and 1.06 μm. The results of probing make it possible to determine the threshold laser energy densities that correspond to the Ge and Si melting and the generation of the Ge ablation plasma versus the amount of deposited Ge and thermophysical parameters of the substrate. The reflection oscillograms are used to obtain the dependences of the melt lifetime on the laser-pulse energy density. [ABSTRACT FROM AUTHOR]

We demonstrate large-area (~600 μm), (111)-oriented, and high-crystallinity, i.e., pseudo-singlecrystalline, germanium (Ge) films at 275°C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al2O3 barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel. [ABSTRACT FROM AUTHOR]

Ge thin films were epitaxially grown on Si(1 1 1) substrates using ultrathin SiO 2 film technique called nanocontact epitaxy. The key to this technique was the use of high density spherical nanodots (NDs) as seed crystals for the epitaxial growth of the Ge films. The seed crystal NDs were elastically strain-relaxed without misfit dislocations so that highly crystalline Ge thin films could be formed. The Ge films were ≈140 nm in thickness and were composed of island-shaped domains with flat Ge(1 1 1) surfaces. The domains had an average size of ≈1 μm and flat surfaces with root mean square of a surface roughness of ≈3 nm. The films had a photoluminescence peak at 0.8 eV, which meant that the films were highly crystalline. [ABSTRACT FROM AUTHOR]

In this work, epitaxial growth of Ge on Si is achieved using magnetron sputtering which is a low-cost and safe method suitable for large-scale production. Smooth surface with RMS roughness of 0.48 nm is obtained at a low deposition temperature of 300 °C. Cyclic thermal annealing is applied to the Ge film reducing the threading dislocation density (TDD) by two orders of magnitude. The in-plane strain in the Ge film changes from compressive to tensile after annealing due to the mismatch in thermal expansion coefficients between Si and Ge. The mechanism of the TDD reduction is investigated revealing formation of dislocation loops and dissociation of dislocations into planar defects at the interface. The Ge epitaxy film on Si may be suitable for use as virtual substrate for the fabrication of III–V high efficiency solar cells. [ABSTRACT FROM AUTHOR]

A method to remove the misfit dislocations and reduce the threading dislocations density (TDD) in the germanium (Ge) epilayer growth on a silicon (Si) substrate is presented. The Ge epitaxial film is grown directly on the Si (001) donor wafer using a "three-step growth" approach in a reduced pressure chemical vapour deposition. The Ge epilayer is then bonded and transferred to another Si (001) handle wafer to form a germanium-on-insulator (GOI) substrate. The misfit dislocations, which are initially hidden along the Ge/Si interface, are now accessible from the top surface. These misfit dislocations are then removed by annealing the GOI substrate. After the annealing, the TDD of the Ge epilayer can be reduced by at least two orders of magnitude to <5 × 106 cm-2. [ABSTRACT FROM AUTHOR]

• A regular arrays of deep pits in Si(0 0 1) substrate were prepared by EBL and PCE. • Arrays of Ge QDs groups were grown by MBE on the pit-patterned Si substrate. • The number of QDs per pit depends on the inter-pit distance. • The mechanism of QDs formation was revealed by the MC simulations. Ordered arrays of Ge quantum dot groups (QDs) were grown on pit-patterned silicon-on-insulator (SOI) substrates with deep pits, prepared by electron beam lithography (EBL) and plasma-chemical etching (PCE). Experiments were carried out for the square and hexagonal pit lattices with the lattice period varied. The QDs were found to be sited at the periphery of pits. It was demonstrated that for both pit lattice types the number of QDs per pit can be controlled by varying the period of the pit lattice. The Monte Carlo (MC) simulations of QDs growth on pit-patterned Si substrates were carried out, using the model, which takes strain into account. The island patterning depending on the inter-pit distance is interpreted as the result of competition between stress-driven QD nucleation and Ge migration downward into the pits, which serve as the sinks for Ge atoms. [ABSTRACT FROM AUTHOR]

Herein stacked layers of germanium and selenium oxide are employed to fabricate heterojunction devices that can perform as a multifunctional thin film transistors (TFT). The stacked layers of Ge and SeO 2 are coated onto ultrasonically cleaned glass and Ag thin film substrates using thermal deposition technique under a vacuum pressure of 1.5 × 10 − 4 mbar. The stacked layers are structurally, morphologically, optically and electrically characterized. It is observed that while amorphous germanium films exhibit two energy band gaps of values of 3.56 and 0.78 eV, amorphous SeO 2 show one band gap of 3.70 eV. The conduction and valence band offsets at the Ge/SeO 2 interfaces are 2.24 eV and 0.68 eV, respectively. Optically, the coating of SeO 2 onto Ge films enhanced the light absorbability of SeO 2 by ~ 50 times (at 2.38 eV) and ~17 times (at 1.71 eV) in the visible and infrared ranges of light, respectively. Formation of Ge/SeO 2 is associated with a redshift and blue shift in the values of the energy band gaps of SeO 2 and Ge, respectively. In addition, the current-voltage characteristic curve analyses have shown that Ag/Ge/SeO 2 /Ag TFTs is of tunneling type showing an estimated peak to valley current ratios of 2.0. The TFT displayed additional functionalities presented by PMOS characteristics, microwave resonators, negative capacitance sources and multiband band stop filters. The features of the devices nominate them for use in microwave technology as band stop filters of notch frequencies of 1.10 and 1.53 GHz. [ABSTRACT FROM AUTHOR]

Direct deposition of high-quality Ge film on Si substrate suitable for fabricating Ge/Si photodiodes was achieved by using plasma-enhanced chemical vapor deposition (PECVD) with GeCl 4 /H 2 as precursors. A tensile-strained, impurity-free, monocrystalline Ge film with a surface roughness of < 1 nm and a threading-dislocation density on the order of 104 cm−2 could be grown at a rate of ca. 80 nm/min at a substrate temperature of 450 °C directly without the need of any kind of buffer layer or post-annealing. When applied to fabricate near-infrared (NIR) photodiodes, a low dark current density and a reasonably good responsivity for the employed photodiode architecture were attained, revealing the potential of this low-temperature fabrication method in monolithic integration of optoelectronic components with Si-based electronic circuits. The success of this technique may be attributed to an atomic-layer-deposition-like process for both nucleation and growth. • Ge is deposited on Si substrate by PECVD with germanium tetrachloride and hydrogen. • Epitaxially-grown monocrystalline Ge film with tensile strain is obtained. • Low threading-dislocation density and surface roughness are achieved. • The Ge film is grown at low substrate temperature without need of post-annealing. • The method is applied to fabrication of Ge/Si photodiode for demonstration. [ABSTRACT FROM AUTHOR]

[Display omitted] Elemental substitution by a different element is a well utilized technique of stabilizing a single-phase compound, in case the parent alloy is multi-phase, and this has been demonstrated specifically in a number of Heusler systems. This can, however, give an increased propensity for chemical disorder as well as adding complexity to synthesis and characterization. In this paper, we present the successful synthesis of a single-phase compound, Co 2 Fe 1.25 Ge 0.75 , by tuning the parent Co 2 FeGe stoichiometry (which exhibits multi-phase structure) rather than introducing a fourth element. The compound is found to crystallize in L2 1 structure (space group # 225). Magnetization measurements reveal Co 2 Fe 1.25 Ge 0.75 has a saturation magnetization as high as 6.7 ± 0.1 μ B /f.u. at 5 K and a Curie temperature of 1135 ± 5 K – both being the highest reported to date for cubic full Heusler alloys to our knowledge. Thin films of Co 2 Fe 1.25 Ge 0.75 deposited on Al 2 O 3 (110) and MgAl 2 O 4 (100) substrates show excellent expitaxial quality, among the reported for Heusler films to date, and exhibit magnetic properties comparable to bulk samples. First principle calculations suggest the system exhibits total energy minimum at the experimentally-observed lattice parameter. Furthermore, the calculations corroborate the observed enhancement in magnetization and point to the importance of on-site Coulomb interactions. While our novel approach of substitution led to the discovery of stable Co 2 Fe 1.25 Ge 0.75 alloy with very high moment and Curie temperature that can be readily grown as a high-quality epitaxial thin film, making it a candidate for device applications, this approach can be taken as a new paradigm for the discovery of novel single-phase Heusler compounds with enhanced magnetic properties. [ABSTRACT FROM AUTHOR]

ITQ-34 zeolite is an interesting catalyst in FCC process due to its three-dimensional medium pore topology. Nowadays, the zeolite ITQ-34 is synthetized as germanosilicate with a zero acid capacity, low stability and sometimes its channels system are partial blocked by the formation of phosphate compounds during the calcination process. For these reasons, to develop a synthesis route to incorporate aluminum in its framework as well as avoid the described problems has a great interest. In the present work is described the possibility to synthesize the zeolite ITQ-34 rich in aluminum, with a low content of germanium and with the total elimination of the phosphate compounds. The zeolite Al-ITQ-34 shows a great catalytic capacity in the propylene production by FCC. [Display omitted] • For the first time, zeolite ITQ-34 is synthetized with aluminum and high acidity. • A novel post-synthesis treatment has been developed. • The elimination of phosphate compounds has been achieved without desaluminization. • Al-ITQ-34 as catalyst shows a high activity in the catalytic cracking of n-decane. • Al-ITQ-34 as catalyst shows a good propylene selectivity. [ABSTRACT FROM AUTHOR]

The relationship between carrier concentration and donor atomic concentration has been determined in n-type Ge films doped with P. The samples were carefully engineered to minimize non-active dopant incorporation by using specially designed P(SiH3)3 and P(GeH3)3 hydride precursors. The in situ nature of the doping and the growth at low temperatures, facilitated by the Ge3H8 and Ge4H10 Ge sources, promote the creation of ultra-low resistivity films with flat doping profiles that help reduce the errors in the concentration measurements. The results show that Ge deviates strongly from the incomplete ionization expected when the donor atomic concentration exceeds Nd = 1017cm-3, at which the energy separation between the donor and Fermi levels ceases to be much larger than the thermal energy. Instead, essentially full ionization is seen even at the highest doping levels beyond the solubility limit of P in Ge. The results can be explained using a model developed for silicon by Altermatt and coworkers, provided the relevant model parameter is properly scaled. The findings confirm that donor solubility and/or defect formation, not incomplete ionization, are the major factors limiting the achievement of very high carrier concentrations in n-type Ge. The commercially viable chemistry approach applied here enables fabrication of supersaturated and fully ionized prototypes with potential for broad applications in group-IV semiconductor technologies. [ABSTRACT FROM AUTHOR]

Thin films of hydrogenated amorphous silicon germanium (a-Si1-xGex:H) alloy are prepared using DC magnetron sputtering method, at a substrate temperature of 150 °C. Silicon and germanium are co-pulverized. All our films are deposited in the same preparation conditions except for those having a germanium content from 27% to 40%. Structural, optical and electrical properties are systematically studied from IR absorption, optical transmission and electrical measurements. Hydrogen content is determined by integrating the wagging mode infrared absorption. The increase of the Ge content from 27% to 40% is responsible for a decrease in optical bandgap of 1.59 to 1.43 eV and a reduction of the total content of hydrogen bonds in both Si-H and Ge-H configurations. A good correlation is observed between the reduction of the optical gap and the increase of one order of magnitude of the dark conductivity. The white light sensitivity shows a significant degradation due to germanium incorporation in the silicon matrix. Therefore, this degradation increases with germanium content. The density of states (DOS) located at the Fermi level g(EF) is estimated from the analysis of capacitance-frequency measurements on Au/a-Si1-xGex:H/c-Si(N+) Schottky structure, in zero bias condition. In our layers, the turn on condition which permits to measure the complete response of the deep states, for 1 kHz frequency, occurs at a relatively high temperature (over 75 °C). The measured density of states increases from 3x1016 cm-3 eV-1 to 3x1018 cm-3 eV-1 when the germanium content increases. This can highlight the narrow correlation between sensitivity degradation and density of states augmentation. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this paper, the results of Ge film deposited by electroplating method was studied and showed the possibility of making a NIRS sensor by the Ge film. Cu/Ti double layer structure could use the cathode electrode on the glass substrate during the GeCl4 electroplating. The deposition rate of electroplating Ge film was 100 nm/h, however, that rate was improved to 570 nm/h by introducing a spacer between Cu thin film and extraction electrode and Ar gas bubbling. The oxygen content of as-deposited film was about 10%, however, this value reduced to lower than 1% by using the Ar bubbling. The deposited film was amorphous and its optical band gap was 0.73 eV. 200 nm-thick Ge film was formed on flexible substrate by electroplating method. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this work we report the surface morphology of amorphous germanium ( a -Ge) thin films (140 nm thickness) following thermal outgassing of SiO 2 /Si substrates. The thermal outgassing was performed by annealing the samples in air at different temperatures from 400 to 900 °C. Annealing at 400 °C in slow (2 °C/min) and fast (10 °C/min) modes promotes the formation of bubbles on the surface. A cross sectional view by transmission electron microscope taken of the sample slow annealed at 400 °C reveals traces of gas species embedded in the a -Ge film, allowing us to propose a possible mechanism for the formation of the bubbles. The calculated internal pressure and number of gas molecules for this sample are 30 MPa and 38 × 10 8 , respectively. Over an area of 22 × 10 −3 cm 2 the density of bubbles obtained at slow annealing (9 × 10 3 cm −2 ) is smaller than that at rapid annealing (6.4 × 10 4 cm −2 ), indicating that the amount of liberated gas in both cases is only a fraction of the total gas contained in the substrate. After increasing the annealing temperature in the slow mode, bubbles of different diameters (from tens of nanometers up to tens of micrometers) randomly distribute over the Ge film and they grow with temperature. Vertical diffusion of the outgas species through the film dominates the annealing temperature interval 400–600 °C, whereas coalescence of bubbles caused by lateral diffusion is detected after annealing at 700 °C. The bubbles explode after annealing the samples at 800 °C. Annealing at higher temperatures, such as 900 °C, leads to surface migration of the film to the exploded bubbles and eventually forming islands of polycrystalline GeO 2 . [ABSTRACT FROM AUTHOR]

Ultrathin C-doped Ge (Ge:C) buffers are used as effective buffer layers to grow thin and smooth Si1-xGe xrelaxed virtual substrates on Si over a wide range of Ge content (x = 0.23, 0.38, 0.50, 0.65, 1) by ultrahigh vacuum chemical vapor deposition. High degree of relaxation (>90%) in thin Si1-xGe xfilms (~50 nm thick) is demonstrated using this approach without additional annealing. Raman data suggest that the Ge:C buffers are still under compressive stress with the subsequent Si1-xGe xlayer growth. A low threading dislocation density of the order of ~ 6 × 104cm-2 is obtained from the relaxed 500-nm Si0.77Ge 0.23 film grown using this method [ABSTRACT FROM AUTHOR]

We present an innovative method for characterizing the strain field in three dimensions in a hetero interface. Largely defocused probe scanning transmission electron microscopy (LDP-STEM) was employed for imaging the inhomogeneous strain field in a germanium (Ge) layer deposited on a silicon (Si) substrate. In the LDP-STEM image, Ge-atomic columns that are relaxed or strained to the Si substrate in the Si/Ge hetero interface were observed to be distinguishable, allowing for the qualitative characterization of the coherency of the crystal growth. Our results revealed that the strain field is locally modulated along the in-plane direction in the Si/Ge hetero interface. [ABSTRACT FROM AUTHOR]

We have observed an irreversible ultrafast crystalline-to-amorphous phase transition in Ge2Sb2Te5 chalcogenide alloy thin film using broadband single-shot imaging spectroscopy. The absorbance change that accompanied the ultrafast amorphization was measured via single-shot detection even for laser fluences above the critical value, where a permanent amorphized mark was formed. The observed rise time to reach the amorphization was found to be ~130-200 fs, which was in good agreement with the half period of the A1 phonon frequency in the octahedral GeTe6 structure. This result strongly suggests that the ultrafast amorphization can be attributed to the rearrangement of Ge atoms from an octahedral structure to a tetrahedral structure. Finally, based on the dependence of the absorbance change on the laser fluence, the stability of the photoinduced amorphous phase is discussed. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effects of the annealing ambient during solid phase crystallization (SPC) on the crystallization temperature of amorphous Ge and the electrical properties of a back-gated poly-crystalline germanium thin film transistor (poly-Ge TFT). Then, it was suggested that a slight amount of oxygen in Ge film and residual oxygen in the annealing ambient play important roles in Ge SPC. We found that the leakage current of poly-Ge TFT was well suppressed by performing SPC in N2 or Ar which contains a slight but appreciable amount of residual oxygen, without decreasing the field effect mobility. In this paper, we discuss effects of the residual oxygen from the view point of defect passivation of Ge. [Copyright &y& Elsevier]

Low-temperature formation (~150°C) of Ge films on insulator is investigated for realization of advanced flexible devices. We propose utilization of Sn as catalyst to enhance the crystallization at low-temperatures. By annealing (150–200°C) of a-Ge/Sn stacked structures formed on insulators, the composition distributions of Ge/Sn layers are inverted, and Sn/poly-Ge stacked structures are obtained. The results demonstrate that the crystallization occurs at 150°C, which is slightly below the eutectic temperatures. This Sn-induced crystallization technique is useful to obtain poly-Ge on low-cost flexible substrates (softening temperature: ~200°C). [ABSTRACT FROM AUTHOR]

Abstract: We investigated the position of Sn atoms in Ge1−xSnx film grown at a low temperature by using the Extended X-ray Absorption Fine Structure (EXAFS) method. Vacancies had been expected to be introduced near the growing surface vicinity of a Sn atom and located at a split-vacancy position due to the binding nature between a Sn atom and a vacancy, which was predicted by the calculation for a bulk model in the literature. However, the EXAFS showed that almost all Sn atoms were located at the substitutional position and did not form a split-vacancy. [Copyright &y& Elsevier]

Abstract: In rapid-melting-crystallization of network Ge-on-insulator (GOI), coalescence of growth-fronts inevitably occurs. To clarify crystallinity of the coalesced regions of two growth-fronts in GOI stripes, scanning electron microscopy and transmission electron microscopy analyses are performed. These analyses reveal that lattice planes of two growth-fronts coherently align without strains for short growth-distance (≤5μm). The lattice planes at growth-fronts start to tilt gradually for growth-distance above 5μm. For intermediate growth-distance (5–150μm), slightly-tilting lattice-planes coherently align without generating any defects, where locally-distributed strains are induced in the coalesced regions. On the other hand, for long growth-distance (≥150μm), grain-boundaries are generated in coalesced regions, and the locally-distributed strains are relaxed. The coherent lattice-alignment for growth-distance below 150μm is attributed to atomic reordering in the coalesced regions, where coalescence occurs at high temperatures around the solidification point of Ge. [Copyright &y& Elsevier]

Abstract: Al-induced crystallization (AIC) enables low-temperature crystallization of amorphous Ge thin films on insulators. We investigated growth promotion of Ge thin films using Ge membranes (1–10nm thickness) that are initially inserted below the Al layer. These Ge insertion layers enhanced supersaturation of Al with Ge, which results in low-temperature AIC (275°C). However, thick (≥3nm) insertion layers result in small grains because of the high nucleation frequency. A 1-nm-thick insertion layer accomplished a growth promotion and yielded large grains of over 100μm in diameter. Moreover, electron backscatter diffraction measurement revealed that the AIC-Ge layer was highly (111) oriented. This low-temperature crystallization technique opens up the possibility for developing Ge-based electronic devices on inexpensive glass substrates, as well as on flexible polymer substrates. [Copyright &y& Elsevier]

The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3V. [ABSTRACT FROM AUTHOR]

The measuring circuit with a voltage generator, which is traditionally used for studying electric properties of glasslike semiconductors, is compared with an alternative version using a current generator. The results obtained in the latter case reflect the interrelation between the memory formation effect and changes in the electrical parameters more comprehensively. A new electric parameter, viz. hold voltage U, which has not been described earlier, is introduced. The relation between U and the memory formation process during the phase transition is established. The effect of emergence of oscillations in the current-limiting regime in the conduction channel in the film is detected. [ABSTRACT FROM AUTHOR]

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

We report efficient zero-bias high-speed top-illuminated p—i—n photodiodes (PDs) with high responsivity fabricated with germanium (Ge) films grown directly on silicon-on-insulator (SOI) substrates. For a 15 μm-diameter device at room temperature, the dark current density was 44.1 mA/cm2 at −1 V. The responsivity at 1.55 μm was 0.30 A/W at 0 V. The saturation of the optical responsivity at 0 V bias revealed that this photodetector allows a complete photo-generated carrier collection without bias. Although the 3-dB bandwidth of the 15-μm-diameter detector was 18.8 GHz at the reverse bias of 0 V, the detector responsivity was improved by one order of magnitude compared with that reported in the literature. Moreover, the dark current of the detector was significantly reduced. [ABSTRACT FROM AUTHOR]

The effect of the doping ratio (B2H6/GeH4) on the structural and electrical properties of boron doped hydrogenated germanium films deposited by the electron cyclotron resonance chemical vapor deposition process has been investigated. By increasing the flow rate of B2H6/GeH4 from 0.025 to 0.125, more boron related radicals are available to desorb hydrogen atoms from the growing surface. This leads to degradation of the structure of the amorphous phase identified by Raman and X-ray diffraction spectroscopy. The incorporation of boron enhances the carrier concentration from 1.65×1019 cm−3 to 2.25×1020 cm−3 and reduces the resistivity from 0.131Ω·cm to 0.018Ω·cm as measured by Hall measurement. These highly conductive boron-doped hydrogenated Ge films can be useful as low resistance doped layer in devices to achieve better performance. Moreover, we are able to deposit highly conductive boron-doped Ge films at a low growth temperature (180°C) and low hydrogen dilution ratio (H2/GeH4 =33), in this study. Such a low temperature process can overcome some problems with high temperature deposition process that limit application in devices. Furthermore, the low hydrogen dilution ratio can minimize an ion bombardment effect on the films. [ABSTRACT FROM AUTHOR]

On the top of Co/Ge(111) films, cobalt oxides are prepared by evaporating Co atoms in an oxygen atmosphere. Depth profiling measurements show a layered structure of a pure Co layer covered by a CoO overlayer. As the CoO thickness increases, the Auger intensity ratio of O KL_2L_2 and Co L3{M{45}}{M{45}} Auger signals increases until reaching a saturated value which shows a CoO layer with a concentration ratio of Co and O close to 1:1. After introduction of CoO overlayers on Co/Ge(111), hysteresis occurs in the longitudinal configuration and CoO/Co/Ge(111) exhibits in-plane anisotropy. A slight reduction of the Kerr intensity occurs due to the oxidation of cobalt at the CoO/Co interface while an enhanced coercive force is observed owing to the imperfection introduced by oxygen to impede the magnetization reversal. Under conditions of cooling in a magnetic field, exchange bias field increases as the sample temperature decreases resulting from the formation of an antiferromagnetic/ferromagnetic interface. [ABSTRACT FROM PUBLISHER]

Germanium (Ge) thin films have been deposited onto the glass substrates by the vacuum evaporation technique. The effect of annealing temperature on the structural and optical properties of the germanium thin films was investigated. The structural and optical properties of thin films were characterized by XRD, SEM, and UV-Vis techniques. XRD results showed that the structure of the deposited thin films changed fromamorphous phase for the films,which deposited at roomtemperature, to crystalline phase for the films, which deposited at high temperature. Optimum temperature to obtain a good crystalline structure was 525°C. The SEM image also showed that the crystallization of the thin films is increased with increasing of annealing temperature. Transmittance and reflectance spectral were used to calculate the absorption coefficient. Two absorption edges in two spectral regions were distinguished according to direct and indirect electron transitions. Energy band gap Eg was calculated by using the Tauc relationship for both direct and indirect electron transitions. The average value of Eg was equal to 0.79 eV and 0.61 eV for direct and indirect transitions, respectively. [ABSTRACT FROM AUTHOR]

A germanium film manufactured by vacuum evaporation was studied and used as a novel resistive anode in Micromegas detectors. Its sheet resistivity characteristics, particularly the thickness dependence and long-term evolution of the film, were demonstrated. Resistive anodes help to suppress the discharge of the detector, but also degrade its counting rate capability. For this reason, a fast grounding method to maintain the rate capability was developed and tested. Micromegas prototypes using the germanium anode were tested and verified. The results indicate that the germanium anode can be a good option not only for Micromegas but also for other micro-pattern gaseous detectors. [ABSTRACT FROM AUTHOR]

• Binder-free nanostructured germanium anode for lithium-ion batteries. • Capacity retention of 95% after 1600 cycles at 1C. • Specific capacity of 1060 mAh g−1 at 10C and 450 mAh g−1 at 60C. • Tested from -30 °C to +60 °C. • Realized by means of a two-step process, easily scalable for industrial applications. The development and the characterization of a nanostructured binder-free anode for lithium-ion batteries exploiting the germanium high theoretical specific capacity (1624 mAh g−1 for Li 22 Ge 5 alloy) is herein presented. This anode secures remarkable performances in different working conditions attaining a 95% capacity retention at 1C (i.e., 1624 mA g−1) after 1600 cycles at room temperature and a specific capacity of 1060 mAh g−1 at 10C and 450 mAh g−1 at 60C. The nanostructured binder-free germanium-based anode shows also strong resilience in terms of temperature tests, being it tested from -30 °C to +60 °C. Indeed, the specific capacity remains unaltered from room temperature up to +60 °C, while at 0 °C the cell is still retaining 85% of its room temperature capacity. In a full-cell configuration with LiFePO 4 as cathode, the Ge anode showed a stable specific capacity above 1300 mAh g−1 for 35 cycles at C/10. Concerning the fabrication procedure, a two-step realization process is applied, where a Plasma Enhanced Chemical vapor Deposition (PECVD) is employed to grow a germanium film on a molybdenum substrate followed by hydrofluoric acid (HF) electrochemical etching, the latter having the scope of nanostructuring the Ge film. Finally, compositional, morphological, and electrochemical characterizations are reported to fully investigate the properties of the binder-free nanostructured germanium anode here disclosed. [Display omitted]. [ABSTRACT FROM AUTHOR]

• Kinetic Monte Carlo simulations of Ge on Si(001) involving surface reconstructions, strain and intermixing. • Intermixing explicitly included through exchange of Ge and Si atoms. • Barrier to intermixing is dependent on strain relaxation. • Quantum dots show Si rich core and Ge rich periphery indicating coupling of intermixing to strain. The morphology of spontaneously self-assembled quantum dots in the Ge/Si(100) heteroepitaxial systems is affected by intermixing of silicon from the substrate with germanium from the deposited film. This is incorporated in an existing kinetic Monte Carlo simulation for strained heteroepitaxial growth through additional processes involving exchange of Si and Ge atoms at the interface. This exchange processes is governed by an intrinsic barrier that is modified by the local bond energy and the elastic energy. The simulations show clearly how intermixing reduces the strain and slows down the formation of quantum dots in the system. Composition maps are used to clearly establish the coupling between strain and intermixing. Silicon from the substrate replaces Ge atoms in the film in the core region of the quantum dot. This is the region with the maximum strain, and other regions with lower strain such as the periphery of the dots have much larger Ge fraction. These results showcase the method here as a powerful tool for study of intermixing in crystal growth. [ABSTRACT FROM AUTHOR]

Variable angle spectroscopic ellipsometry (VASE) was employed to examine the photoinduced effect on the optical properties of Ge 25 Sb 5 Se 70 thin films, that were prepared by thermal evaporation method. The measurements were carried out at room temperature and in the UV–vis–NIR (near infrared) spectral region for photon wavelengths from 280 to 1000 nm. For data analysis, we employed linear combination consist from two Cody–Lorentz (CL) dispersion model in the entire measured photon range. The photo bleaching (increase in bandgap) was identified by this model. The behavior of the Cody–Lorentz model parameters with the time of light illumination is discussed in detail. To obtain a good fitting to the variation of fundamental CL amplitude with the time of exposer, we proposed a simple phenomenological model based on the alternation of bond formation and breaking. Good agreement between calculated and experimental data is obtained. [ABSTRACT FROM AUTHOR]

The discovery of Weyl and Dirac fermions has greatly encouraged the study of topological aspects in condensed matter physics, especially the discovery of ferromagnetic type-II Weyl semimetals such as CeAl X (X ​= ​Si, Ge). However, the evolution process of the physical characteristics of CeAl X during the Ge/Si substitution has not been studied in detail, and the relevant researches were mostly based on their polycrystalline samples. Herein, the millimeter level single crystals of CeAl(Si 1-x Ge x) were prepared and studied systemically. It can be concluded that the higher Ge content leads to the bigger lattice constants and electrical resistivity, but the lower magnetic transition temperature (T C) and magnetoresistance (MR). The electrical conductivity at room temperature and the MR at 2 ​K of CeAl(Si 0.9 Ge 0.1) can even reach up to 6.35 and 6.55 times bigger than that of CeAl(Si 0.1 Ge 0.9), respectively. In addition, CeAl(Si 1-x Ge x) would change from n -type to p -type after "x" exceeds 0.5. The continuously tunable isoelectronic Ge/Si substitution makes CeAl(Si 1-x Ge x) an excellent platform for exploring the exotic electromagnetic responses of topological materials. The millimeter level single crystals of CeAl(Si 1-x Ge x) were prepared and studied systemically. The higher Ge content tends to bring the bigger unit cell parameters, but the lower magnetic transition temperature (T C) and smaller magnetoresistance (MR). [Display omitted] The highlights of this work include: • The size of CeAl(Si 1-x Ge x) single crystals can even reach the millimeter level. • The unit cell parameters of CeAl(Si 1-x Ge x) become larger with the increasing "x". • The more Ge content, the lower T C and MR in the CeAl(Si 1-x Ge x) series. • CeAl(Si 1-x Ge x) would change from n -type to p -type after "x" exceeds 0.5. [ABSTRACT FROM AUTHOR]

We introduced Sn as a potential dopant in Ge 2 Sb 2 Te 5 films to improve the thermoelectric performance. A systematic study of the thermoelectric properties of Sn doped Ge 2 Sb 2 Te 5 films is presented. The effects of Sn doping content on chemical bonds were studied and Sn element was verified to combine with Te. The generation of additional LDOS peaks and the flatting of conduction band in Sn doped system promote the optimization of Ge 2 Sb 2 Te 5 's carrier concentration near the Fermi level and enhance its seebeck coefficient. The carrier concentration is optimized through occupation of Ge cation vacancies by Sn and formation of Sn Te antistie defect. The adjustment of carrier concentration and carrier effective mass accounts for the decrease in resistivity and the increase in seebeck coefficient. A competitively high-power factor of 0.7 mW/K2m was reached in 20 W Sn doped amorphous film at 323 K and a maximal PF value of 1.88 mW/K2m was achieved in 50 W Sn doped crystalline film at 723 K. This work reveals that Sn doping contributes to the improvement of the thermoelectric properties of the Ge 2 Sb 2 Te 5 films. • Isovalent doping Sn improves the thermoelectric properties of Ge 2 Sb 2 Te 5 films. • The electron delocalization promotes reduction of the crystalline band gap. • Sn occupies vacancies and Te sites to modulate the carrier concentration. • Band flattening and additional LDOS peaks enhance the seebeck coefficient. [ABSTRACT FROM AUTHOR]

Zn-doped Ge2Sb2Te5 (GST) thin films are deposited on glass substrates by an electron-beam evaporation technique in an ultra-high vacuum. GST mixed with 5%, 10%, 20% Zn is used. Through in situ resistance measurements, an increase of crystalline temperature in Zn-doped GST was observed. From absorption spectra, the optical bandgap values of 10% Zn-doped GST in different structures are estimated to be 1.1, 0.9, and 0.7 eV, respectively, which are slightly wider than that of pure GST. A prototype phase-change memory (PCM) device using GST thin film doped with Zn was fabricated. The current-voltage test results of the devices show better switching performances in both SET and RESET processes than that of the device using pure GST film. The threshold voltage is greatly increased with the adding of Zn atom with fixed proportion, which can weaken the interaction during the read and write operation of PCM. [ABSTRACT FROM AUTHOR]

Abstract: In this work we have studied boron doping of hydrogenated amorphous germanium a-Ge:H and polymorphous germanium (pm-Ge:H) in low regimes, in order to compensate the material from n-type (due to oxygen contamination that commonly occurs during plasma deposition) to intrinsic, and in this manner improve the properties that are important for infrared (IR) detection, as activation energy (Ea) and temperature coefficient of resistance (TCR). Electrical, structural and optical characterization was performed on the films produced. Measurements of the temperature dependence of conductivity, room temperature conductivity (σRT), Ea and current–voltage characteristics under IR radiation were performed in the compensated a-Ge:H and pm-Ge:H films. Our results demonstrate that, effectively, the values of Ea, TCR and IR detection are improved on the a-Ge:H/pm-Ge:H films, using boron doping in low regimes, which results of interest for infrared detectors. [Copyright &y& Elsevier]

Abstract: Growth of low-temperature metal-free crystallized Ge film was investigated using inductively coupled plasma-assisted DC magnetron sputtering. The films were deposited both without and with inductively coupled plasma. The films deposited by a conventional DC magnetron sputtering system had randomly oriented crystalline structures. However, the addition of inductively coupled plasma developed crystal phase from an amorphous to a preferred oriented crystalline with increasing sputtering power. The optical band gaps of the amorphous and crystalline phases were 0.96eV and 0.7eV, respectively. [Copyright &y& Elsevier]

Abstract: Changes in the microstructural and electrical properties of carbon-doped Ge2Sb2Te5 during thermal annealing under N2 and air atmospheres are investigated. The occurrence of compositional and structural changes was found to depend on the annealing conditions, and in particular, on the out-diffusion of germanium atoms. The thick oxidation layer generated during air annealing prevented germanium out-diffusion, leading to structural changes but no compositional changes. In contrast, germanium out-diffusion occurred during annealing under N2, leading to compositional changes but preventing structural changes. [Copyright &y& Elsevier]

The Ge-like indirect band gap of Ge1-x-ySixSny alloys has been determined over an extended y > x range using photoluminescence spectroscopy from films grown on Ge-buffered Si substrates. It is found that the compositional dependence of this transition can be fit with a bilinear expression of the form (in eV): [formula]. These energies are significantly below the prediction from a simple linear interpolation between Si, Ge, and α-Sn, revealing a large negative bowing in the compositional dependence similar to that found earlier for direct transitions. The direct-indirect crossover boundary is found to lie along the compositional line y = (0.062 ± 0.014) + (0.76 ± 0.23)x, which in the limit x → 0 agrees with earlier results for the binary Ge1-ySny alloy. [ABSTRACT FROM AUTHOR]

Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 °C for a short period (< 20 s). The films were grown on Si(001) substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged (> 20 s) rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si—Ge mixing at high temperature. [ABSTRACT FROM AUTHOR]

Germanium-tin (Ge1−xSnx) p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) were fabricated using a strained Ge0.985Sn0.015 thin film that was epitaxially grown on a silicon-on-insulator substrate with a relaxed Ge buffer layer. The Ge buffer was deposited using a two-step chemical vapor deposition growth technique. The high quality Ge0.985Sn0.015 layer was grown by solid source molecular beam epitaxy. Ge0.985Sn0.015 pMOSFETs with Si surface passivation, TaN/HfO2 gate stack, and nickel stanogermanide [Ni(Ge1−xSnx)] source/drain were fabricated on the grown substrate. The device achieves an effective hole mobility of 182 cm2/V·s at an inversion carrier density of 1 × 1013 cm−2. [ABSTRACT FROM AUTHOR]

Abstract: In this report we present a novel strategy in selective epitaxial growth on top of Si pillars, which results in a tessellated Ge film, composed by self-aligned micron-sized crystals in a maskless process. Modelling by rate equations the morphology evolution of fully facetted crystal profiles is extensively outlined, showing an excellent prediction of the peculiar role played by flux shielding among microcrystals, in the case of dense array configuration. Crack formation and substrate bending, caused by the mismatch in thermal expansion coefficients, are eliminated by the mechanical decoupling among individual microcrystals, which are also shown to be dislocation- and strain-free. The method has been also tested for Si1−x Ge x alloys, with compositions ranging from pure silicon to pure germanium. There are ample reasons to believe that this approach could be extended to other material combinations and substrate orientations, actually providing a technology platform for several device applications. [Copyright &y& Elsevier]

Highlights: [•] Epitaxial growth of Si1−x Ge x on Si at 350°C has been achieved by RTCVD. [•] Si2H6 and GeF4 are used as source gases. [•] GeF4 can be reduced into Ge by the reductant gas Si2H6 in RTCVD system at 350°C. [•] For 780nm-thick film, a TDD of ∼7.0×105cm−2 and RMS roughness of 1.44nm are achieved. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of Ge x Ga5S(95− x ) (x =25, 30, 35) prepared by melt quenching technique were deposited on glass slides by thermal evaporation technique under vacuum. A surface profiler was employed to characterize the morphology of the thin films. Optical transmission spectra measured by a UV/VIS/NIR spectrometer, in the spectral range from 400 to 2500nm, have been used to determine the refractive index, with Swanepoel's method. The thicknesses of the films were calculated with good accuracies better than 1.06%. It has been found that the refractive index of the Ge x Ga5S(95− x ) samples increases with increasing ratio of Ge/S. Optical band gaps were calculated from Tauc's extrapolation procedure and were found to decrease from 2.8eV to 2.59eV with x increasing from 25 to 35. The structural units of the films were characterized by Raman spectroscopy, indicating that in addition to the basic structural units of edge-shared and corner-shared Ge(Ga)S4 tetrahedra, there are S–S homopolar bonds in S-rich films, and the main band of the films slightly shifted to higher frequency and broadened as the ratio of Ge/S increased. The behavior of refractive index and optical band gap were interpreted in terms of structural change of atoms involved in the thin films. [Copyright &y& Elsevier]

Abstract: Electrical switching studies on amorphous Si15Te74Ge11 thin film devices show interesting changes in the switching behavior with changes in the input energy supplied; the input energy determines the extent of crystallization in the active volume, which is reflected in the value of SET resistances. This in turn, determines the trend exhibited by switching voltage (Vt) for different input conditions. The results obtained are analyzed on the basis of the amount of Joule heat generated, which determines the temperature of the active volume. Depending on the final temperature, devices are rendered either in the intermediate state with a resistance of 5∗102 Ω or the ON state with a resistance of 5∗101 Ω. [Copyright &y& Elsevier]

Abstract: Germanium thin film electrodes show a reversible Na-ion reaction at potentials around 0.15/0.6V. The reaction is accompanied with a reversible capacity close to 350mAhg−1, which matches the value expected for the formation of NaGe. The electrode capacity retention is stable over 15cycles but subsequently declines. However, using fluoroethylene carbonate (FEC) electrolyte additive positively improves capacity retention and promotes the formation of a thinner SEI. Mechanical degradation due to repeated expansion/shrinkage coupled with SEI formation are the main sources of capacity decline. Preliminary XRD results do not reveal the formation of crystalline phases at full (dis)charge. The excellent charge rate up to 340C highlights the high potential of nanosized germanium as Na-ion anode. [Copyright &y& Elsevier]

Strain relaxation of thin Ge layers grown by carbon-mediated epitaxy at 50°C on Si(001) was investigated for a multi-step growth procedure. Additionally, the impact of the post-growth annealing temperature on the strain relaxation obtained for a single carbon-mediated growth step was analyzed. The degree of relaxation was monitored in situ by reflection high energy electron diffraction and ex situ by high-resolution x-ray diffraction and transmission electron microscopy. For multi-step growth, relaxation occurs mainly during the first cycle (growth and annealing). Full relaxation is already achieved after 3–4 cycles. The relaxation process during a single growth cycle can be divided into three sections: annealing up to 200°C is sufficient to trigger most of the strain relaxation. After annealing up to 450°C, the film lattice parameter already equals the Ge bulk value, though the layer shows a rough surface. Only an annealing step up to 650°C results in a smooth surface and interface. Smooth and fully relaxed Ge films of only 26nm thicknesses were obtained by carbon-mediated growth. [ABSTRACT FROM AUTHOR]