Bulk Ge Research Articles

GeSn-based p-i-n photodiodes with strained active layer on a Si wafer

We report an investigation of GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained. The results show that (a) the response of the Ge/GeSn/Ge heterojunction photodiodes is stronger than that of the reference Ge-based photodiodes at photon energies above the 0.8 eV direct bandgap of bulk Ge (<1.55 μm), and (b) the optical response extends to lower energy regions (1.55–1.80 μm wavelengths) as characterized by the strained GeSn bandgap. A cusp-like spectral characteristic is observed for samples with high Sn contents, which is attributed to the significant strain-induced energy splitting of heavy and light hole bands. This work represents a step forward in developing GeSn-based infrared photodetectors.

Electrical characterization studies of p-type Ge, Ge1−ySny, and Si0.09Ge0.882Sn0.028 grown on n-Si substrates

The electrical properties of p-type Ge, Ge1−ySny, and Si0.09Ge0.882Sn0.028 samples grown on n-type Si substrates using ultra-high vacuum chemical vapor deposition have been investigated as a function of temperature. Degenerate parallel conducting layers were found in all Ge/Si, Ge1−ySny/Si, and Si0.09Ge0.882Sn0.028/Si samples, which are believed to be associated with dislocation defects at the interface produced by the lattice mismatch between the two materials. These degenerate conducting layers affect the electrical properties of all the thin epitaxial films. Additionally, temperature dependent Hall-effect measurements show that these materials exhibit a conductivity type change from p to n at around 370–435 K. The mobilities of these samples are generally lower than that of bulk Ge due to carrier scattering near the interface between the epitaxial layer and the Si substrate and also due to alloy scattering. Detailed behavior of temperature-dependent conductivity of these samples is also discussed.

LA-ICP-MS analyses of minor and trace elements and bulk Ge isotopes in zoned Ge-rich sphalerites from the Noailhac – Saint-Salvy deposit (France): Insights into incorporation mechanisms and ore deposition processes

The increasing worldwide demand in germanium (Ge) is driving renewed research for understanding its geological cycle and the factors controlling its concentration in minerals. The advent of accurate, high-resolution trace element analysis by LA-ICP-MS, as well as the advances in MC-ICP-MS technique for Ge isotopes in sulphides, has enhanced studies in this field. Ge isobaric interferences, standard calibration and data interpretation remain outstanding issues needing to be addressed for more precise and comprehensive LA-ICP-MS analyses.An integrated mineralogical and geochemical study was carried out on typical sphalerite (ZnS) samples from the main Ge deposit in western Europe: the vein-type Zn–Ge–Ag–(Pb–Cd) deposit of Noailhac – Saint-Salvy (Tarn, France). In situ coupled measurements of trace elements and S isotopes were performed using LA-ICP-MS and SIMS, respectively, together with bulk Ge isotopes by MC-ICP-MS. Principal component analyses revealed element clusters antithetically distributed within distinct zoning types in sphalerite: sector zonings are enriched in Cu, Ge, Ga, Sb and As, whereas rhythmic bandings (dark brown bands primarily) are enriched in Fe, Cd, In and Sn. This typical distribution points to crystallographic controls on trace element uptake during sphalerite growth, occurring with concomitant microscale variations in fluid compositions at the fluid–crystal interface. Regardless of the zoning type, in all spots, Cu contents approach the sum of tri- and tetravalent cations (Ge, Ga, In, etc.) so that Cu could provide charge-balance for the entire set of coupled substitution mechanisms responsible for the incorporation of the whole range of trace elements in this sphalerite. Strong binary correlations suggest direct substitutions as Zn2+↔(Fe2+, Cd2+) and coupled substitutions as 2Zn2+↔Cu++Sb3+, 3Zn2+↔Ge4++2Ag+, and 3Zn2+↔In3++Sn3++□ (vacancy) despite no clear evidence for the presence of Sn4+.δ74GeNIST3120a in bulk sphalerite varies from −2.07±0.37‰ to +0.91±0.16‰ (2σ SD) and positively correlates with bulk Ge content. This indicates considerable Ge isotopic fractionation within sphalerite during low-T hydrothermal deposition and zoning processes, associated with possible microscale open system fluid mixing. The trace element features in sphalerite from Saint-Salvy compared with those of other deposits confirm their use as discriminators among genetic types of ores (e.g., high In contents for magmatic-related deposits, and Ge for low-temperature deposits).

Influence of Implantation Damages and Intrinsic Dislocations on Phosphorus Diffusion in Ge

Influence of the implant-induced damages and the threading dislocations during germanium (Ge) epitaxy was investigated on the phosphorus diffusion in Ge. An adequate n-type junction was formed by 650°C rapid thermal annealing of the implanted bulk Ge. It is observed that for epitaxial Ge on Si substrate, there was an enhanced local phosphorus diffusion approaching the Ge/Si interface. A diffusion model considering the enhancement by defects is proposed to sufficiently explain the phosphorus diffusion profiles in Ge. The intrinsic dislocation-enhanced phosphorus diffusivity found at least three orders of magnitude larger than that in the absence of dislocations.

Contacting a Conjugated Molecule with a Surface Dangling Bond Dimer on a Hydrogenated Ge(001) Surface Allows Imaging of the Hidden Ground Electronic State

Fabrication of single-molecule logic devices requires controlled manipulation of molecular states with atomic-scale precision. Tuning molecule-substrate coupling is achieved here by the reversible attachment of a prototypical planar conjugated organic molecule to dangling bonds on the surface of a hydrogenated semiconductor. We show that the ground electronic state resonance of a Y-shaped polyaromatic molecule physisorbed on a defect-free area of a fully hydrogenated surface cannot be observed by scanning tunneling microscopy (STM) measurements because it is decoupled from the Ge bulk states by the hydrogen-passivated surface. The state can be accessed by STM only if the molecule is contacted with the substrate by a dangling bond dimer. The reversibility of the attachment processes will be advantageous in the construction of surface atomic-scale circuits composed of single-molecule devices interconnected by the surface dangling bond wires.

Luminescence from Germanium and Germanium on Silicon

We present an overview on generation of direct gap photo- and electroluminescence in Ge bulk wafers, Ge thin films deposited on Si, and Ge p-i-n diodes prepared on Si substrates. We analyzed the emission in a spectral range from 0.45 eV to 0.95 eV, covering the radiation caused by direct gap transitions, the indirect one, and also the luminescence related to transition on dislocations. The temperature and excitation level strongly influence the intensities of direct and indirect photoluminescence in bulk samples. As it could be expected, high temperature and excitation favour the generation of direct gap luminescence. Intrinsic bulk Ge shows a quadratic dependence of the direct gap luminescence on the excitation and a sub-quadratic one for the indirect. The photoluminescence spectra taken from intrinsic Ge on Si layers show features related to dislocations. There are two spectral regions associated with dislocation recombination. At room temperature one is at around 0.45 eV and the other at 0.72 eV. We found strong direct gap radiation from the Ge p-i-n diodes with intrinsic, highly dislocated active area (dislocation density of about 108-1010 cm-2). There is a threshold current density of 8 kA/cm2, at which the direct band luminescence becomes a super-quadratic. The dependence of the radiation intensity on the excitation is governed by a power law with exponent of 1.7 before reaching that threshold and 4.5 after exceeding it. Above the threshold the dislocation radiation shows similar dependence on the excitation as the direct band luminescence.

Comparative Leakage Analysis of GeOI FinFET and Ge Bulk FinFET

We present a comparative leakage analysis of germanium-on-insulator (GeOI) FinFET and germanium on bulk substrate FinFET (Ge bulk FinFET) at device and circuit levels. Band-to-band tunneling (BTBT) leakage-induced bipolar effect is found to result in an amplified BTBT leakage for GeOI FinFET. Device and circuit designs to mitigate the amplified BTBT leakage of GeOI FinFETs are suggested. The effectiveness of various high threshold voltage technology options including increasing channel doping, increasing gate length and drain-side underlap for leakage reduction is analyzed.

Novel epitaxial silicon interlayer for junction engineering in aggressively-scaled germanium photodetectors

A new technique which uses an ultra-thin silicon interlayer in germanium photodetectors for junction engineering is demonstrated. A 5 nm epitaxially grown silicon layer was effective in preventing phosphorus diffusion into bulk Ge at 625 °C. Abrupt junction profile was achieved in thin 250 nm Ge PDs which led to improved bandwidth performance during low voltage operations (at 1V or less).

Spin and energy relaxation in germanium studied by spin-polarized direct-gap photoluminescence

Spin orientation of photoexcited carriers and their energy relaxation are investigated in bulk Ge by studying spin-polarized recombination across the direct band gap. The control over parameters such as doping and lattice temperature is shown to yield a high polarization degree, namely larger than 40$%$, as well as a fine tuning of the angular momentum of the emitted light with a complete reversal between right- and left-handed circular polarization. By combining the measurement of the optical polarization state of band-edge luminescence and Monte Carlo simulations of carrier dynamics, we show that these very rich and complex phenomena are the result of the electron thermalization and cooling in the multivalley conduction band of Ge. The circular polarization of the direct-gap radiative recombination is indeed affected by energy relaxation of hot electrons via the $X$ valleys and the Coulomb interaction with extrinsic carriers. Finally, thermal activation of unpolarized $L$ valley electrons accounts for the luminescence depolarization in the high temperature regime.

Effects of reduced-oil corn distillers dried grains with solubles composition on digestible and metabolizable energy value and prediction in growing pigs1

Two experiments were conducted to determine the DE and ME content of corn distillers dried grains with solubles (corn-DDGS) containing variable ether extract (EE) concentrations and to develop DE and ME prediction equations based on chemical composition. Ether extract content of corn-DDGS ranged from 4.88 to 10.88% (DM basis) among 4 corn-DDGS samples in Exp. 1 and from 8.56 to 13.23% (DM basis) among 11 corn-DDGS samples in Exp. 2. The difference in concentration of total dietary fiber (TDF) and NDF among the 4 corn-DDGS sources was 2.25 and 3.40 percentage units, respectively, in Exp. 1 but was greater among the 11 corn-DDGS sources evaluated in Exp. 2, where they differed by 6.46 and 15.18 percentage units, respectively. The range in CP and ash were from 28.97 to 31.19% and 5.37 to 6.14%, respectively, in Exp. 1 and from 27.69 to 32.93% and 4.32 to 5.31%, respectively, in Exp. 2. Gross energy content among corn-DDGS samples varied from 4,780 to 5,113 kcal/kg DM in Exp. 1 and from 4,897 to 5,167 kcal/kg DM in Exp. 2. In Exp. 1, the range in DE content was from 3,500 to 3,870 kcal/kg DM and ME content varied from 3,266 to 3,696 kcal/kg DM. There were no differences in ME:DE content among the 4 corn-DDGS sources in Exp. 1, but ME:GE content differed (P = 0.04) among sources (66.82 to 74.56%). In Exp. 2, the range in DE content among the 11 corn-DDGS sources was from 3,474 to 3,807 kcal/kg DM and ME content varied from 3,277 to 3,603 kcal/kg DM. However, there were no differences in DE:GE, ME:DE, or ME:GE among sources in Exp. 2. In Exp. 1, no ingredient physical or chemical measurement [bulk density (BD), particle size, GE, CP, starch, TDF, NDF, ADF, hemicellulose, EE, or ash)] was statistically significant at P ≤ 0.15 to predict DE or ME content in corn-DDGS. In Exp. 2, the best fit DE equation was DE (kcal/kg DM) = 1,601 - (54.48 × % TDF) + (0.69 × % GE) + (731.5 × BD) [R(2) = 0.91, SE = 41.25]. The best fit ME equation was ME (kcal/kg DM) = 4,558 + (52.26 × % EE) - (50.08 × % TDF) [R(2) = 0.85, SE = 48.74]. Apparent total tract digestibility of several nutritional components such as ADF, EE, and N were quite variable among corn-DDGS sources in both experiments. These results indicate that although EE may be a good predictor of GE content in corn-DDGS, it is not a primary factor for predicting DE or ME content. Measures of dietary fiber, such as ADF or TDF, are more important than EE in determining the DE or ME content of corn-DDGS for growing pigs.

Analysis of Threshold Current Behavior for Bulk and Quantum-Well Germanium Laser Structures

We analyze the optical gain of tensile-strained, n-germanium (n-Ge) material taking bandgap narrowing (BGN) for heavily doped Ge into account. Both the direct bandgap and indirect bandgap are narrowed by 60 meV. Our new modeling explains the wide lasing spectrum of 1520-1700 nm in electrically pumped Ge lasers. The calculated materials gain can reach 1000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> when the injected carrier density is ~mid-10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> with a combination of 0.25% tensile strain and 4.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> n-type doping. The threshold current density is estimated to be 0.53 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for an optimized edge-emitting double-heterojunction Ge device, comparable to bulk III-V lasers. We also review current progress on Ge quantum-well (QW) structures. The threshold current density of most Ge QW structures is similar to bulk Ge. Only tensile-strained QWs show reduced threshold currents.

The thermoelectric properties of Ge/SiGe modulation doped superlattices

The thermoelectric and physical properties of superlattices consisting of modulation doped Ge quantum wells inside Si1−yGey barriers are presented, which demonstrate enhancements in the thermoelectric figure of merit, ZT, and power factor at room temperature over bulk Ge, Si1−yGey, and Si/Ge superlattice materials. Mobility spectrum analysis along with low temperature measurements indicate that the high power factors are dominated by the high electrical conductivity from the modulation doping. Comparison of the results with modelling using the Boltzmann transport equation with scattering parameters obtained from Monte Carlo techniques indicates that a high threading dislocation density is also limiting the performance. The analysis suggests routes to higher thermoelectric performance at room temperature from Si-based materials that can be fabricated using micro- and nano-fabrication techniques.

Observation of optical spin injection into Ge-based structures at room temperature

Non-zero spin polarization induced by optical orientation was clearly observed at room temperature in a Ge/Ge0.8Si0.2 quantum well grown on Ge and a Ge layer grown on Si by molecular beam epitaxy, whereas it was absent in bulk Ge. This occurred because indirect-gap photoluminescence (PL), which can obscure the spin-polarization information carried by the direct-gap PL, was quenched by unintentional growth-related defects in the epitaxial layers. Such interpretation was confirmed by applying time gating that effectively removed the indirect-gap PL characterized by a slower rise time, which allowed us to demonstrate the existence of room-temperature spin polarization in bulk Ge.

Topaz as an important host for Ge in granites and greisens

AbstractThe composition of topaz from different granites and greisen in the Krušné Hory/Erzgebirge area was investigated using electron microprobe analysis (EMPA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). All topaz grains are rich in F (17.9 19.8 wt.%, 1.73 1.90 a.p.f.u.) and the most important minor/trace elements are P, Ge and Ga. Contents of P up to 1 wt.% P2O5 (0.025 a.p.f.u.) were found in topaz from the strongly peraluminous P-rich magmatic systems at Podlesí. Regardless of genetic type, topaz from granites typically contains 50 100 ppm Ge. The greatest amounts (up to 204 ppm Ge) were found in topaz from quartz-topaz-apatite greisen in Krásno. In fractionated granites and greisens, topaz is calculated to contain 23 87% of the bulk Ge content in the rock. In contrast, topaz does not concentrate Ga. The Ga content of topaz (typically 5 35 ppm in S-type granites, &lt;10 ppm Ga in A-type granites) is usually smaller than the bulk Ga content of the rock. In addition, up to 16 ppm Sc, 23 ppm Sn and &gt;400 ppm Fe may be present.

Potential for growth of Si–Ge bulk crystals by modified FZ technique

The technique for crucibleless crystal growth of silicon and its alloy with germanium is developed on the basis of the floating zone (FZ) setup equipped with an additional so-called axial heating process (AHP) heater. The heater forms around itself the melt zone being suspended by forces of surface tension between its top surfaces and the growing crystal, as well as between the top surfaces of the AHP heater and the feeding rod. To investigate into the problem of the capillary stability of the pulling process, numerical computations of shaping of the free Si and Ge melt surface during the crystal pulling were performed. The dependences of the crystal radius and the thickness of the melt film on the parameters of the process are analyzed. It is demonstrated that, in the modified FZ method, the thickness of the melt layer between the crystal and the heater can be considerably larger than the capillary constant. A number of Si and Si–Ge crystals with a diameter up to 15mm are grown. The range of a Si–Ge melt layer, which one could establish as high as possible, was found to be equal to 11–18mm.

Characterization of Ge/Si0.16Ge0.84 multiple quantum wells on Ge-on-Si virtual substrate using piezoreflectance spectroscopy

A Ge/Si0.16Ge0.84 multiple quantum well (MQW) structure grown on a Ge-on-Si virtual substrate (Ge-VS) was characterized by using temperature dependent piezoreflectance (PzR) technique. Signals from every relevant portion of the sample, including Ge-VS, MQW and barriers were observed. The band gap blue-shifted and valence band splitting in the vicinity of the direct band-edge transitions of Ge revealed that the Ge-VS is compressively strained. A comprehensive analysis of the PzR spectra led to the identification of various quantum-confined interband transitions. In addition, the parameters that describe the temperature dependence of the excitonic transition energies were evaluated and found to be similar to that of the bulk Ge.

Light absorption enhancement in closely packed Ge quantum dots

Multilayers of Ge quantum dots (QDs, 3 nm in diameter) embedded in SiO2, separated by SiO2 barrier layer (3, 9, or 20 nm thick), have been synthesized by sputter deposition and characterized by transmission electron microscopy and light absorption spectroscopy. Quantum confinement affects the optical bandgap energy (1.9 eV for QDs, 0.8 eV for bulk Ge); moreover, the absorption probability greatly depends on the QD-QD distance. A strong electronic coupling among Ge QDs is evidenced, with a significant increase of the light absorption efficiency when the QD-QD distance is reduced. These data unveil promising aspects for light harvesting with nanostructures.

“Y function” method applied to saturation regime: Apparent saturation mobility and saturation velocity extraction

In this work, we extend the “Y function” method to the saturation regime of MOSFET operation. This allowed us for the first time to extract a low charge apparent mobility up to high drain voltage and consequently the saturation velocity without the need of source drain series resistance correction. The method has successfully been applied to silicon (Si) and germanium (Ge) bulk technologies and the nonconvergence of linear mobility and saturation velocity improvement is highlighted.

Computational Modeling of the Size Effects on the Optical Vibrational Modes of H-Terminated Ge Nanostructures

The vibrational dispersion relations of porous germanium (pGe) and germanium nanowires (GeNWs) were calculated using the ab initio density functional perturbation theory with a generalized gradient approximation with norm-conserving pseudopotentials. Both pores and nanowires were modeled using the supercell technique. All of the surface dangling bonds were saturated with hydrogen atoms. To address the difference in the confinement between the pores and the nanowires, we calculated the vibrational density of states of the two materials. The results indicate that there is a slight shift in the highest optical mode of the Ge-Ge vibration interval in all of the nanostructures due to the phonon confinement effects. The GeNWs exhibit a reduced phonon confinement compared with the porous Ge due to the mixed Ge-dihydride vibrational modes around the maximum bulk Ge optical mode of approximately 300 cm−1; however, the general effects of such confinements could still be noticed, such as the shift to lower frequencies of the highest optical mode belonging to the Ge vibrations.

Room temperature photoluminescence of Ge-on-insulator structures formed by rapid melt growth

Room temperature photoluminescence (PL) was observed along 50 μm long Ge strips on insulator on bulk Si substrates fabricated by rapid melt growth. The PL peaks evidently exhibited a redshift from the origin to the end of the Ge strip because of the shrinkage of the direct bandgap of Ge. Moreover, PL intensities increased along the direction of lateral epitaxial growth primarily because of the decrease in the energy difference between the direct and indirect gaps of Ge. The change in the Ge band structure, which facilitated changes in PL peaks and intensities, was found to have resulted from the variation of tensile strain ratios and Si fractions along Ge strips. Furthermore, the PL intensity at the end of the strip was one magnitude higher than that of bulk Ge, which indicates the high quality of Ge-on-insulator structures.