Search

Structural and magnetic properties of Mn 5 (Si x Ge 1-x) 3 thin films were investigated. Ferromagnetic Mn 5 Ge 3 and anti-ferromagnetic Mn 5 Si 3 thin films have been synthesized and characterized as these compounds exhibit interesting features for the development of spintronics. Here, Mn 5 (Si x Ge 1-x) 3 thin films were grown on Ge(111) substrates by co-deposition using molecular beam epitaxy. Crystalline thin films can be produced with controlled Si concentrations ranging from 0 to 1. The thin films were relaxed by dislocations at the interface with the substrate. A lattice parameter variation was observed as the Si content increased, which is comparable to previous works done in bulk. Reflection high-energy electron diffraction diagrams and X-ray diffraction profiles showed that lattice parameters a and c are shrinking and that the surface roughness and crystallinity degrade as the Si amount increases. Magnetometric measurements revealed a ferromagnetic behavior for all Si concentrations. The measured average ferromagnetic moment per manganese atom decreased from 2.33 to 0.05 μ B /Mn atom. No ferro to anti-ferromagnetic transition was observed contrary to the bulk Mn 5 (Si x Ge 1-x) 3 compound. • Mn 5 (Si x Ge 1-x) 3 thin films are epitaxially grown on Ge(111) by molecular beam epitaxy. • Mn 5 (Si x Ge 1-x) 3 films with a Si concentration up to x = 0.6 are synthesized. • Si concentration and the structural and magnetic properties are correlated. [ABSTRACT FROM AUTHOR]

We have researched on the formation of crystalline silicon-germanium (c-SiGe) films as a new material for bottom cells of silicon-based multi-junction solar cells. We conducted solid phase crystallization (SPC) from amorphous SiGe (a-SiGe) precursors with 80–70% Ge fraction deposited on n-type [100] single crystalline silicon (c-Si) substrates. Preferential crystal growth following the orientation of c-Si substrates is successfully done by the SPC at temperatures from 500 to 950 °C, although X-ray diffraction indicates that the c-SiGe films have the mosaic structures consisting of crystalline domains with several tens of nanometers. Lower SPC temperature is more appropriate to obtain better crystallinity SiGe with larger domain size and lower mosaicity as long as the crystallization occurs. The inter-diffusion between the a-SiGe precursors and Si substrates occurs at relatively high SPC temperatures (≥ 850 °C), and the Ge fraction in the c-SiGe films becomes lower than that in the a-SiGe precursors. [ABSTRACT FROM AUTHOR]

We have investigated the lateral solid phase crystallization (SPC) of amorphous germanium (a-Ge) precursors on single crystalline silicon (c-Si) substrates with a silicon dioxide (SiO 2 ) stripe structure. The a-Ge layers were deposited on c-Si with SiO 2 stripes at 100 °C and SPC was carried out at 375–385 °C. The crystallization in a-Ge layers is only nucleated on c-Si substrates and thus, the preferential crystalline growth occurred along the normal orientation of the c-Si substrates, with no crystallization of the Ge layers nucleated on a-Ge layers over SiO 2 layers, except near the c-Si/SiO 2 boundary. As a result we have obtained lateral preferential crystalline growth of c-Ge of large grain size by SPC from a-Ge films on c-Si over SiO 2 stripes, where the preferential crystalline growth distance in a-Ge on SiO 2 increased from 3 to 5 μm, when the annealing temperature increased from 375 to 385 °C. [ABSTRACT FROM AUTHOR]

• GeO x films are grown by plasma-enhanced atomic layer deposition (PE-ALD). • Increase in monoxide bond was observed for PE-ALD GeO x film grown at 250 °C. • GeO x at 250 °C exhibits high refractive index of 1.73 compared to typical value of 1.63. • GeO x in this study shows high density of ∼ 3.5 g/cm3 with low etch rate in water. Germanium oxide (GeO x) films were grown by plasma-enhanced atomic layer deposition (PE-ALD) at 70, 130, 190 and 250 °C, using tetrakis (dimethylamino)-germanium as a precursor and O 2 plasma as a reactant. For GeO x film grown at 250 °C, a relatively low growth-per-cycle (GPC) of 0.55 Å/cycle and high refractive index of 1.73 was observed as compared to the GPC and refractive index for the films grown at 70, 130, and 190 °C. Meanwhile, the areal portion of the germanium monoxide (GeO) peak to germanium dioxide (GeO 2) in the Ge 3d core-level spectra of X-ray photoelectron spectroscopy increased proportional to the refractive index of the film. When estimating the mean molar mass of the GeO x films from the Lorentz-Lorenz equation, low molar mass was obtained from the GeO x film grown at 250 °C indicating germanium monoxide bond formation in the film. As the PE-ALD grown GeO x films exhibited high densities of about 3.5 g/cm3 almost close to the typical density value (3.6 ∼ 3.7 g/cm3) of germanium oxide film, low water-etch rates of 5 ∼ 10 nm/s were achieved for the PE-ALD grown GeO x films, compared to the reported etch rates of 60 ∼ 100 nm/s for germanium dioxide films. In summary, PE-ALD process for growing GeO x films has the advantage of obtaining high film density with controllable water-etch rate. [ABSTRACT FROM AUTHOR]

• Behavior of amorphous Ge films on nonwettable SiO 2 surfaces is studied. • Agglomeration of Ge film into compact particles begins at 350 °C. • Ge particle shapes have a large aspect ratio. • Deep minima in reflection spectra are due to optical resonances in particles. • Multipole excitations and close particle packing cause broadband antireflection. The dewetting phenomenon that occurs during annealing of Ge films after their deposition on oxidized Si surfaces at room temperature is studied. The agglomeration of Ge films into compact particles begins at temperature as low as 350 °C. The particle shapes become closer to spherical as the annealing temperature is increased to 700 °C. The reflectance spectra of samples coated with dense arrays of compact Ge particles are measured in the wavelength range of 350–1200 nm. They contain two broad minima, at which the reflection decreases by a factor of 5–10, compared to the bare substrate reflection. The minimum in the long-wavelength region of the spectrum is associated with the excitation of magnetic and electric dipole resonances in individual Ge particles. The appearance of a deeper minimum in the short-wavelength region can be attributed to the excitation of quadrupole resonant modes in combination with the effect of small interparticle spacings. The coatings from the thus obtained particles exhibit strong and broadband antireflection properties. [ABSTRACT FROM AUTHOR]

This paper focuses on a strained Ge channel N type metal-insulator semiconductor transistor and demonstrates the biaxial compressive strain thin Ge films grown on Si substrates by ultra-high vacuum chemical vapor deposition. The performance enhancement is also exhibited. The drive current and subthreshold swing of the strained Ge transistor is seen to be better than the Si control device. The on-off current ratio reaches an order of eight without sacrificing the leakage current. For mobility enhancement, the Ge device exhibits an enhancement greater than 100% compared with the Si device. The development of strained Ge N type and P type metal-insulator semiconductor transistors with thin Ge film for complementary metal-oxide semiconductor (CMOS) technology without the III-V material may allow nanoscale feasibility for future generations and be compatible with current CMOS processes. [ABSTRACT FROM AUTHOR]

Amorphous Ge 30.5 Se 69.5 and Ge 39.5 Se 60.5 films were prepared by thermal evaporation from previously synthetized bulk glasses. We did not observe a shift in the optical band gap values associated with the change in film thickness for the virgin and annealed states of the thin films. Certain minor changes in the optical band gap values were explained by the change in the chemical composition and by the change in the sample disorder. Both ultraviolet and visible and far infrared spectra indicate that annealed Ge 39.5 Se 60.5 thin films are practically insensitive to the illumination while Ge 30.5 Se 69.5 thin films show a reversible photodarkening. The observed reversible changes of the optical band gap for Ge 30.5 Se 69.5 thin films were also not dependent on the film thickness. The network structural rigidity, which can be combined with a quick relaxation of the light induced excitation directly back to the ground state, was suggested as the reason for the absence of reversible photodarkening in Ge 39.5 Se 60.5 thin films. [ABSTRACT FROM AUTHOR]

In this work, epitaxial Ge films grown on Si by magnetron sputtering were annealed by diode laser as a replacement for conventional thermal annealing to reduce the threading dislocation density (TDD). After laser scans of millisecond exposure time, improvement of crystallinity and increase in tensile strain are observed in the Ge films. TDD of the Ge film is reduced by two orders of magnitude from 10 10 cm − 2 to 10 8 cm − 2 after only three laser scans. Diode laser annealing is a fast and low-cost method to effectively reduce TDD in epitaxial Ge films on Si. [ABSTRACT FROM AUTHOR]

Effects of carbon (C) atoms on solid-phase epitaxial growth of Ge on Si(100) have been studied. C and Ge layers were deposited on Si(100) substrates at low temperature (150–300 °C) by using solid-source molecular beam epitaxy (MBE) system and subsequently annealed at 650 °C in the MBE chamber. The surface morphology after annealing changed depending on deposited amounts of C and deposition temperature of Ge. Ge dots were formed for small amounts of C while smooth Ge films were formed by large amounts of C varying with the Ge deposition temperature. The surface morphology after annealing was also affected by the as-deposited Ge crystallinity. The change in surface morphology depending on the amounts of deposited C was considered to be affected by the formation of Ge–C bonds which relieved the misfit strain between Ge and Si. The crystallinity of Ge deteriorated with increasing C coverage due to the incorporation of insoluble C atoms in the shape of both dots and films. [ABSTRACT FROM AUTHOR]

In this work, the growth and the fabrication of heavily doped germanium plasmonic antennas for mid-infrared applications are reported. By tuning the phosphorus doping concentration and the antenna geometrical parameters, plasma frequencies for targeting the 8–15 μm spectral region are achieved. 1 μm thick, heavily doped (2.3 × 10 19 cm − 3 ) germanium was used to fabricate dipole antennas of 800 nm width with a gap spacing of 300 nm which demonstrate resonance frequencies around 13 μm and 13.5 μm for 2 μm and 3 μm long structures, respectively. This technology has the potential to be used for mid-infrared sensing applications of hazardous gases and liquids. [ABSTRACT FROM AUTHOR]

• Growth methods allow to tune the phase formation in the manganese germanide thin films. • The effective heat of formation model is a suitable framework to describe the phase formation. • The epitaxy of Mn5Ge3 on Ge(111) expands the range of the thermal stability of this compound. We have studied the stability of manganese germanide thin films grown on Ge(111) substrates by three different growth methods: solid phase epitaxy, reactive deposition epitaxy and co-deposition. By combining X-ray diffraction and magnetic measurements, we demonstrate that we can form either Mn 5 Ge 3 or Mn 11 Ge 8 thin films depending on the growth processes. In the case of solid phase epitaxy, we explain the phase formation sequence by taking into consideration the kinetic and thermodynamic processes involved. Tuning phase formation of the manganese germanide thin films was determined using in situ X-ray diffraction and the effect of the thin film thickness on the Mn 5 Ge 3 thermal stability was investigated. [ABSTRACT FROM AUTHOR]

High-temperature transmittance spectrum of germanium films was obtained by a Fourier Transform infrared spectroscopy with a high-temperature accessory. The optical constants were determined by transmittance spectrum fitting with a Gaussian oscillator as the dispersion model. The analysis results showed that both the refractive index and extinction coefficient increased with the increasing temperature. The square of the refractive index increased linearly with the increasing temperature. The higher the temperature was, the faster the absorption coefficient increased. The germanium films were deposited on chemical vapor deposition ZnS substrates by ion-beam-assisted deposition. The region of temperature was between room temperature and 773 K, and the analysis spectrum was between 2000 nm and 5000 nm. [ABSTRACT FROM AUTHOR]

Optical properties of a p -Ge 0.99 Sn 0.01 film grown on an n -Si substrate have been investigated as a function of temperature and excitation laser intensity using photoreflectance (PR) spectroscopy. The Ge 0.99 Sn 0.01 film was grown by ultra-high vacuum chemical vapor deposition method. Room temperature PR spectrum shows a dominant signal assigned to a direct transition from the conduction Γ valley to valence band at around 0.73 eV. The transition to spin-orbit split-off band is also observed at around 1.0 eV. In addition, Franz–Keldysh oscillations (FKOs) due to the internal electric field are observed above the direct bandgap transition energy. The direct transition energy obtained by an analysis of FKO extremum was 0.728 eV at room temperature. The internal electric fields are reduced as the laser excitation intensity increases due to the photovoltage effect. The temperature dependence of direct transition energy was also investigated. [ABSTRACT FROM AUTHOR]

Several sets of Ge films were grown by ion beam sputter deposition under systematic variation of ion beam parameters (ion species and ion energy) and geometrical parameters (ion incidence angle and polar emission angle). The films were characterized concerning thickness, growth rate, mass density, structural properties and composition. The film thicknesses show a cosine-like angular distribution, and the growth rates were found to increase with increasing ion incidence angle and ion energy. All films are amorphous and the average mass density was found to be (4.3 ± 0.2) g/cm 3 , without a systematic relation to ion energy and geometrical parameters. Slightly higher mass densities were found for Ge films grown by sputtering with Xe than for sputtering with Ar. The Ge films contain a fraction of inert gas atoms from backscattered primary particles. This fraction is found to be higher for sputtering with Ar than for sputtering with Xe. The fraction of inert gas atoms increases with increasing polar emission angle and increasing ion incidence angle. Raman scattering experiments revealed also systematic shifts of the characteristic Raman mode. The shifts are tentatively assigned to the change of the Ge particle densities caused by the incorporation of inert gas particles. There seem to be also slight changes in short range ordering. The experimental data are discussed with respect to the known energy and angular distributions of the sputtered and backscattered particles. [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]

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 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]

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]

Abstract: Single-crystalline-like epitaxial germanium thin films with hall mobility values as high as 833cm2/Vs have been demonstrated on inexpensive polycrystalline metallic substrates. The dependence of mobility of p-type and n-type germanium films on the deposition temperature has been examined and correlated to microstructural changes. The importance of crystallographic orientation of Ge to achieve these high mobility values has been verified. The mobilities of the epitaxial germanium films on the film thickness for p-type and n-type films with multi-layer architecture with different epitaxial intermediate layers have been investigated. Results show that the increased mobility with increasing germanium film thickness is not just due to crystallographic texture improvement, but could also be a result of decreasing defect density. [Copyright &y& Elsevier]

Abstract: A time iterative surface analytical study of as-deposited and chlorinated nanoporous germanium (PGe) films oxidized in Class 1000 cleanroom air at room temperature is reported. Deconvolution of X-ray photoelectron spectroscopy (XPS) Ge 3d core level spectra for as-deposited films showed stable levels of Ge2O, GeO, and Ge2O3 with air exposure duration, while growth of GeO2 was observed with logarithmic rate dependence, characteristic of low temperature oxide growth on fully dense Ge films. In contrast, chlorinated PGe showed an initially reduced surface and growth of all GeOx phases for up to 10h of air exposure, after which only GeO2 was observed to grow with similar kinetics to that observed on the as-deposited films. Deconvolution of the XPS Cl 2p core level spectra showed continual loss of chlorine for up to ~10h of air exposure after which no Clents could be resolved. The results reported herein reveal logarithmic growth of each of the GeOx phases on chlorinated PGe during displacement of chlorine with oxygen. Once chlorine is removed from the surface, the percentages of Ge2O, GeO, and Ge2O3 suboxides remain constant with only GeO2 growth with further air exposure. These results offer insight into the early stages of oxide growth on porous germanium indicating the formation of a suboxide transition layer onto which GeO2 grows. [Copyright &y& Elsevier]

• Ge diffusion in SiO 2 is influenced by the stoichiometric state of the film. • Ge chemical bonds formed during implantation are highly dose and depth dependent. • Ge diffusion is enhanced for low-fluences or slightly over-stoichiometric oxides. • O co-implantation enables the standardization of Ge nanocrystals size distribution. The thermally activated diffusion of germanium atoms implanted in the middle of SiO 2 layers has been studied by Rutherford Backscattering Spectroscopy (RBS), X-ray Photoelectron Spectroscopy (XPS), µ-Raman spectroscopy and X-Ray Diffraction (XRD), with and without the presence of co-implanted 16O− ions. The important role of implantation-induced defects, in particular atomic recoil of silicon and oxygen atoms, on the well-known asymmetric redistribution of germanium depth-profile is discussed for samples solely implanted with germanium, as a function of the fluence. This is shown how both the stoichiometric state of the implanted SiO 2 layer and their chemical environment influence the mobility of Ge atoms. For samples co-implanted with oxygen, RBS shows an enhancement of germanium diffusion under thermal activation at 1100 °C as long as the oxygen over-saturation of the SiO 2 film is not achieved. This change in the germanium diffusion is associated to the formation of GeO x compounds during the implantation, as shown by XPS measurements. This is responsible, during the annealing step, of the formation of highly mobile GeO at low oxygen fluences and less mobile GeO 2 at higher fluences. Combination of XRD and µ-Raman analyses is used to highlight the impact of the co-implanted O atoms on the size dispersion of germanium nanocrystals. [ABSTRACT FROM AUTHOR]

• We employ radio-frequency sputtering with Ge chips set on a ceramic TiO 2 target. • Both Ge and TiO 2 crystallize at conditions exceeding 3.8 at.%Ge and 823 K. • Representative average diameter of Ge nanocrystals is approximately 10 nm. • Photocurrent maximizes at approximately 11 at.%Ge and 800 K. We investigate optimization of the Ge concentration and substrate temperature to maximize the photocurrent of a nanocomposite thin film containing Ge nanocrystals (NCs) embedded in a TiO 2 matrix prepared on a p-type Si substrate. The films were deposited on the substrate using radio-frequency sputtering with a target of a ceramic TiO 2 disc with Ge chips at substrate temperatures ranging from 573 K to 873 K. Both Ge and TiO 2 in the composite crystallized at substrate temperatures exceeding 823 K. Scanning transmission electron microscopy revealed that the typical size of the Ge NCs was 7 nm. The maximum photocurrent was obtained at a Ge concentration and substrate temperature of approximately 11 at.% and 800 K, respectively. [ABSTRACT FROM AUTHOR]

• Lattice-matched Ge/GeSiSn layers were examined by Raman spectroscopy • Crystallinity of the Ge/GeSiSn layers improves as the Ge layers become thicker • Crystallinity depends on the ratio of the growth times of Ge and GeSiSn layers Lattice-matched Ge/GeSiSn layers were formed on Ge substrates by sputter epitaxy, and the effects of the thicknesses of the Ge and GeSiSn layers on crystallinity of the Ge/GeSiSn layers were examined by Raman spectroscopy. First, a GeSiSn layer was formed on a Ge substrate, and then a Ge layer was formed on it. Raman spectra were obtained from the formed Ge/GeSiSn layers, and crystallinity was evaluated by using the full width at half maximum (FWHM) values of the Raman peaks. The growth temperature was about 300°C. The light wavelength of the Raman spectroscope used in this study was 532 nm. A single Raman peak was observed at the Raman spectra obtained from the Ge/GeSiSn layers, which was derived from the upper Ge layers due to the penetration length. From the Raman spectra, crystallinity of the Ge/GeSiSn layers depended on the thicknesses of the Ge and GeSiSn layers. Crystallinity decreased as the GeSiSn layer became thicker and increased as the Ge layers became thicker. We found that the normalization of the FWHM values by the ratio of the film thicknesses or growth times of the Ge and GeSiSn layers can be useful for evaluating the growth conditions. [ABSTRACT FROM AUTHOR]

• We characterized the Si 1-x Ge x etch rate using HNO 3 /HF mixtures as the etchant. • We studied the mechanism of Si 1-x Ge x etching comparing blanket and lateral etching. • We investigated the effect of structural factors on lateral etching of Si 1-x Ge x. A gate-all-around device, considered as a key structural design for improving performance and density, requires selective etching to obtain nanostructure channels. We investigated the wet etching of epitaxial Si 1-x Ge x films with various HNO 3 /HF-based chemical etchants to elucidate the mechanism of selective etching of Si 1-x Ge x versus pure Si. Blanket etching was performed on Si 1-x Ge x single-layer and lateral etching was performed on Si/Si 1-x Ge x /Si multi-layer with three different Ge concentrations (x = 0.13, 0.24, and 0.30). In both cases of etching, our results show that the Si 1-x Ge x layer with higher Ge concentration was etched faster. We found that the Si 1-x Ge x etch rate decreased consistently with decreasing HF in both cases, while the slope of the etch rate lowers as the Ge concentration decreases with the blanket etching of Si 1-x Ge x. We postulated that the decrease in the slope of the Si 1-x Ge x etch rate with low Ge concentration occurs due to the difficulty of hole injection into the surface of Si 1-x Ge x , which has a lower valence band offset. In contrast, for the case of lateral etching of Si 1-x Ge x , we found that the slopes of the etch rate are similar to each other irrespective of Ge concentrations. We suggest that the similarity of the slopes is due to the sufficiency of holes, which is supplied not only by HNO 3 but also from adjacent Si layers into the Si 1-x Ge x layer. Furthermore, we investigated the effect of structural factors on the lateral etching of Si 1-x Ge x to apply a selective etching process in Si/Si 1-x Ge x /Si multi-layer to obtain Si nanostructures. We found that the lateral etch rate of Si 1-x Ge x in Si/Si 1-x Ge x /Si multi-layers can be reduced owing to the oxide of adjacent Si layers in the etched tunnel, which is not completely removed by HF during the etching process. [ABSTRACT FROM AUTHOR]

• Low loss germanium oxide grown through ion-assisted alternating current sputtering. • Sputtering in the hysteresis regime affects film loss. • High uniformity across large area. • Low losses are achievable without the need for post-deposition process steps. • Propagation losses of 0.1 dB/cm for 638 nm were obtained for slab waveguide. We report low optical loss germanium oxide (GeO 2) thin films which have been deposited by low pressure ion-assisted alternating current dual magnetron sputtering of germanium targets in an oxygen plasma environment. The germanium oxide films ranging from 0.7- to 1.0-µm-thick were fabricated at low temperature and high deposition rates of 6–38 nm/min on silicon and thermally oxidized silicon substrates. The refractive index of the films was determined through variable angle spectroscopic ellipsometry and found to be 1.6051 on average at a wavelength of 638 nm. The films were shown to be near stoichiometric through Rutherford backscattering spectroscopy analysis and displayed sub-nanometer roughness when measured with atomic force microscopy. High peak-to-valley uniformity on a 3-inch substrate with relative deviation of 0.8% was achieved. We characterized the attenuation of the GeO 2 thin films from visible to near-infrared wavelengths and observed it to be as low as 0.1 dB/cm at 638 nm for deposition rates of 8 nm/min. This deposition technique provides complementary metal-oxide-semiconductor compatible GeO 2 thin films suitable for integrated photonics applications and is promising for the fabrication of other dielectric waveguide materials. [ABSTRACT FROM AUTHOR]

• We achieved the chalcogenide film with high resistance. • Three resistance relaxation states in chalcogenide glasses film are explained. • An un simplified Boltzmann formula. The resistance of chalcogenide glass Ge x As y Se 1–x–y film is difficult to be observed due to the electrons pinned near the Fermi level, the large electron binding energy, and the large film resistance. Because the resistance is too large, the test method of Hall effect cannot be used to investigate the electrical properties for chalcogenide glass. In this work, the resistance relaxation states of a series of Ge x As y Se 1–x–y films with different components are observed by reducing the resistance under non-equilibrium temperature conditions from 300 to 440 K, and then the local state electron transport mechanism is investigated. It is interesting that the electrical properties parameters show three relaxation states: 1) The conventional trend is that the conductivity decreases with the increase of temperature. 2) One particular trend is that the resistance presents a wavy shape as the temperature increases. 3) The most special trend is that as the temperature is raised during the conductivity measurements, the conductivity increases before decreases after having reach a certain temperature. Computer calculation results show that the Boltzmann fit formula is more suitable than simply Boltzmann formula for Ge x As y Se 1–x–y chalcogenide film in terms of a low-mobility semiconductor with deep Fermi level and hopping conduction. Through calculations, it is found that three relaxation states are decided by the density of the localized states at Fermi level. [ABSTRACT FROM AUTHOR]

• Interface trap density increased due to the intermixing of Si and Ge. • Surface roughness and interface trap density was worse after etching of SiGe from Si substrate • Thin Si epitaxial layer on etched substrate had better interface trap density and surface roughness. The gate-all-around structure is a promising candidate for future generations of advanced metal-oxide semiconductor field-effect transistor technologies, as it provides higher drive current and low-power operation. The commonly-suggested nanowire structure uses a selective etching technique in the silicon/silicon-germanium multilayer to reveal the channel area. The revealed Si surface is rough, however, due to the missing atoms and remnants of Si 1-x Ge x. This leads to increased interfacial state density, which degrades device performance, such as subthreshold voltage swing. Regarding the usage of high-k metal gates on the channel area, the issue of this rough surface, and the subsequent increase of the dangling bonds after etching, should be properly addressed. In this study, we report the enhanced roughness and density of interface state by applying a Si capping layer. The epitaxial Si 0.87 Ge 0.13 layer, with a thickness of 30 nm on the Si substrate, was removed by an etchant consisting of nitric acid, hydrofluoric acid, and acetic acid, after which a 1-nm thick Si capping layer was epitaxially grown onto the surface. Atomic Force Microscopy was used to measure the roughness, and X-ray Photoelectron Spectroscopy was conducted to characterize the atomic bonds on the surface. A 10-nm thick SiO 2 film was deposited using the Atomic Layer Deposition process to characterize the capacitance-voltage curve and interface trap density. The Si-capped sample exhibited half of the surface roughness of the un-capped sample, and exhibited a 30% lower interface trap density, by mitigating the impact of wet etching. [ABSTRACT FROM AUTHOR]

• S i 1 − x G e x films with x > 0.9 were prepared on Si(111) by liquid phase epitaxy. • The Si atoms of S i 1 − x G e x films were supplied by melt-back etching. • A self-modulated compositionally graded buffer layer was originally found. • S i 1 − x G e x films covering the entire substrate were achieved in a single step. High germanium (Ge) content silicon germanium (S i 1 − x G e x) epilayers with the composition x over 0.9 were prepared on Si(111) substrate by liquid phase epitaxy (LPE). As known, a lattice mismatch high to the degree of 4.2% between Ge and Si has made the direct growth of high Ge content S i 1 − x G e x on Si substrate quite challenging for LPE. However, self-organized S i 1 − x G e x films grown with a grading composition were recognized by cross-sectional scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The film structure obtained could be further divided into three layers according to the distribution variation of elemental composition. The initial S i 1 − x G e x layer showed a tardy grading in the Ge composition from 0.1 to 0.15 within a thickness of 21 - 33 μm. Then, the second layer was featured by an abrupt crossover to Ge-rich condition in the composition distribution within a thickness of about 8 - 12 μm. Finally, the top S i 1 − x G e x layer demonstrated a consistently high Ge content (x > 0.9) within a thickness of 2 – 4 μm. It is found that using a Ge-Sn initial growth solution, commencing the LPE at 950 °C, and terminating the growth at an appropriate temperature suggested by the Ge-Sn phase diagram present a feasible methodology to prepare high Ge content SiGe epilayer on Si(111) substrate. In this work, we focus on exploring the formation mechanism of high Ge content SiGe epilayer on Si by LPE by combining the SEM/EDS analysis results with both Si-Sn and Ge-Sn phase diagrams. [ABSTRACT FROM AUTHOR]