Doped Germanium Research Articles

Interface Damage of Protective Layer in TEM Lamella Preparation for Highly Doped Ge Substrate

This work reports on the TEM sample preparation of highly doped germanium (Ge) sample using focused ion beam (FIB) technique. The method of the deposition of protective layer is varied to observe the damage at the interface of protective layer and specimen surface. It is shown that TEM lamella prepared using the FIB inevitably contains the surface damage induced by the deposition of protective layer. An effective method of controlling the damage at the interface of protective layer and specimen surface is by introducing a two-step deposition technique of protective layer using electron beam and ion beam, with smooth interface can be observed when the imaging was performed for the cross-sectional TEM.

Germanium doping of cubic GaN grown by molecular beam epitaxy

We present a study of germanium as an alternative to silicon for n-type doping of cubic GaN. We find that Ge is a well-suited donor impurity. Our layers were grown by plasma-assisted molecular beam epitaxy on 3C-SiC/Si (001) substrates. Germanium-doped layers were fabricated with donor concentrations ranging over several orders of magnitude up to 3.7 × 1020 cm−3. For comparison, silicon-doped layers with donor concentrations of up to 3.8 × 1019 cm−3 were also grown. Incorporation of germanium into the cubic GaN layers was verified by time-of-flight secondary ion mass spectrometry. The crystalline quality of our layers was analyzed using high-resolution x-ray diffraction. Germanium- as well as silicon-doped layers with donor concentrations above 1019 cm−3 exhibited an increase of the dislocation density with increasing dopant concentration. The surface topography of our layers was investigated by atomic force microscopy. Comparable values for the surface roughness were measured for germanium- as well as silicon-doped layers. Optical properties were investigated by photoluminescence spectroscopy at 13 K. Doping with silicon resulted in a spectrally slightly narrower luminescence than doping with germanium. Donor concentrations and carrier mobilities were determined by Hall effect measurements at room temperature and we observe 20% higher electron mobilities for Ge-doping compared to Si-doping in the case of high dopant concentrations.

Multi-Energy X-Ray Tomography of an Optical Fiber: The Role of Spatial Averaging.

Using a commercial X-ray tomography instrument, we have obtained reconstructions of a graded-index optical fiber with voxels of edge length 1.05 µm at 12 tube voltages. The fiber manufacturer created a graded index in the central region by varying the germanium concentration from a peak value in the center of the core to a very small value at the core-cladding boundary. Operating on 12 tube voltages, we show by a singular value decomposition that there are only two singular vectors with significant weight. Physically, this means scans beyond two tube voltages contain largely redundant information. We concentrate on an analysis of the images associated with these two singular vectors. The first singular vector is dominant and images of the coefficients of the first singular vector at each voxel look are similar to any of the single-energy reconstructions. Images of the coefficients of the second singular vector by itself appear to be noise. However, by averaging the reconstructed voxels in each of several narrow bands of radii, we can obtain values of the second singular vector at each radius. In the core region, where we expect the germanium doping to go from a peak value at the fiber center to zero at the core-cladding boundary, we find that a plot of the two coefficients of the singular vectors forms a line in the two-dimensional space consistent with the dopant decreasing linearly with radial distance from the core center. The coating, made of a polymer rather than silica, is not on this line indicating that the two-dimensional results are sensitive not only to the density but also to the elemental composition.

Germagraphene as a promising anode material for lithium-ion batteries predicted from first-principles calculations.

Finding electrode materials with high capacity is a key challenge for developing lithium-ion batteries (LIBs). Graphene was once expected to be a promising candidate, but it turns out to be too inert to interact with Li. Here, by using first-principles calculations, we predict that germanium doped graphene, termed as Germagraphene, which has been achieved in a recent experiment, is a promising LIB anode material. We find that at the optimal Ge concentration, which corresponds to the chemical formula C17Ge, the specific capacity for Germagraphene can be as high as 1734 mA h g-1, over four times larger than that of graphite. We show that the material has good electrical conduction before and after Li adsorption. We also investigate the diffusion process of Li on Germagraphene, and find that the diffusion barrier is low (∼0.151 eV), implying fast Li diffusion. The calculated average intercalation potential is very low (∼0.03 V), which is beneficial for increasing the working voltage for full-cells. In addition, during the process of Li intercalation, the lattice change for the material is quite small (∼0.48%), implying a good cycling performance. These results suggest that Germagraphene could be a promising high-capacity anode material for LIBs.

High germanium doping of GaN films by ammonia molecular beam epitaxy

Gallium Nitride (GaN) grown by ammonia molecular beam epitaxy and doped with elemental Germanium (Ge) is presented. Growth studies varying the GaN growth rate, substrate growth temperature and the elemental Ge flux reveal several incorporation dependencies. Ge incorporation increases with flux, as expected, and a doping range from ∼1017 cm−3 to 1020 cm−3 was readily achieved. A strong substrate temperature dependence on the electrical properties of films grown is observed, with an optimal growth temperature of 740 °C, lower than standard GaN growth conditions for ammonia molecular beam epitaxy. Compensation effects at higher growth temperatures are suspected, as observed with other techniques. Crystallographic defects are apparent at the highest doping concentrations from electrical and optical measurements, however thin layers of such highly doped films are of great interest for contact layers and tunnel junctions in devices.

Plasmonic mid-infrared third harmonic generation in germanium nanoantennas

We demonstrate third harmonic generation in plasmonic antennas consisting of highly doped germanium grown on silicon substrates and designed to be resonant in the mid-infrared frequency range that is inaccessible with conventional nonlinear plasmonic materials. Owing to the near-field enhancement, the result is an ultrafast, subdiffraction, coherent light source with a wavelength tunable between 3 and 5 µm, and ideally overlapping with the fingerprint region of molecular vibrations. To observe the nonlinearity in this challenging spectral window, a high-power femtosecond laser system equipped with parametric frequency conversion in combination with an all-reflective confocal microscope setup is employed. We demonstrate spatially resolved maps of the linear scattering cross section and the nonlinear emission of single isolated antenna structures. A clear third-order power dependence as well as mid-infrared emission spectra prove the nonlinear nature of the light emission. Simulations support the observed resonance length of the double-rod antenna and demonstrate that the field enhancement inside the antenna material is responsible for the nonlinear frequency mixing.

Understanding the Effect of Germanium as an Efficient Auxiliary Pre‐Dopant in Carbon Nanotubes on Enhancing Oxygen Reduction Reaction

AbstractIn this study, sulfur‐doped carbon nanotubes with germanium as a pre‐dopant (SGe‐CNTs) are successfully prepared by sequential doping of germanium and sulfur, and their activity oxygen reduction reaction (ORR) activity is evaluated. As comparison, Ge‐doped CNTs and S‐doped CNTs are synthesized. The electrochemical results reveal that both Ge‐doping and S‐doping could improve the ORR activity of CNTs. In the synthesis process of SGe‐CNTs, germanium is deemed to be an efficient auxiliary pre‐dopant, since germanium modifies the microstructure of CNTs, and germanium content on the surface of Ge‐CNTs decreases dramatically after sulfur doping. Meanwhile, sulfur content on the surface of SGe‐CNTs is much higher than that of S‐CNTs with equivalent sulfur‐comprising dopants. Due to the Ge pre‐doping effect and synergistic effect of S/Ge doping, SGe‐CNTs with appropriate ratio of Ge and S atoms exhibit prominently enhanced ORR performance compared with those of single Ge‐ or S‐doped CNTs. By virtue of the outstanding ORR performance, SGe‐CNTs materials are expected to be highly active and cost‐effective ORR electrocatalysts in metal‐air batteries and alkaline fuel cells. The excellent ORR catalytic performance of SGe‐CNTs could be ascribed to the auxiliary Ge pre‐doping effect.

Monolayer doping of germanium by phosphorus-containing molecules

The DPP (diethyl 1-propylphosphonate) and ODPA (octadecylphosphonic acid) molecules are studied as precursors for the monolayer doping (MLD) of germanium. Their adsorption behaviour is investigated, revealing different physicochemical interactions between the phosphorus-containing molecules and the Ge surfaces. It is discovered that DPP adsorption occurs after the oxidation of Ge surface, while the ODPA undergoes chemisorption on –H terminated surfaces. Quantitative phosphorus analysis demonstrates that in the first case more than one monolayer is formed (from 2 to 4), while in the second a single monolayer is formed. Moreover, the analysis of phosphorus diffusion from the surface layers into the Ge matrix reveals that conventional thermal annealing processes are not suitable for Ge injection due to a higher activation energy of the process in comparison with silicon. On the contrary, pulsed laser melting is effective in forming a doped layer, owing to the precursor’s decomposition under UV light.

All-Solid Photonic Crystal Fiber for Dispersion Compensation Over <inline-formula> <tex-math notation="LaTeX">$S+C+L$ </tex-math> </inline-formula> Wavelength Bands

A dual-concentric-core photonic crystal fiber (DCPCF) with low germanium doping is numerically investigated for dispersion compensation. The inner cladding is formed by a fluorine-doped concentric ring which is used to increase the index slope difference between two supermodes and eliminate the sensitivity of dispersion characteristic to air holes in the inner cladding of traditional structures. The proposed DCPCF can compensate for the dispersion and dispersion slope of a standard single-mode fiber (SMF) at 1550-nm wavelength. The $K$ value matches with that of SMF very well. Moreover, it can realize an effective compensated dispersion range of ±0.8 ps/nm/km from 1.458 to $1.626~\mu \text{m}$ wavelength which covers the $S+C+L$ bands. The geometric parameters on dispersion characteristic are investigated. The sensitivity of the fiber dispersion and the effective compensated dispersion to ±2% and ±5% variation in the optimum parameters is studied for practical fabrication.

Coordinate dependent diffusion analysis of phosphorus diffusion profiles in gallium doped germanium

We have analyzed phosphorus diffusion profiles in an In0.01Ga0.99As/In0.56Ga0.44P/Ge germanium structure during phosphorus co-diffusion with gallium for synthesis of the germanium subcell in multi-junction solar cells.. Phosphorus diffused from the In0.56Ga0.44P layer simultaneously with gallium diffusion into the heavily gallium doped germanium substrate thus determining the specific diffusion conditions. Most importantly, gallium and phosphorus co-diffusion produces two p–n junctions instead of one. The phosphorus diffusion profiles do not obey Fick’s laws. The phosphorus diffusion coefficient DP depth distribution in the specimen has been studied using two methods, i.e., the Sauer–Freise modification of the Boltzmann–Matano method and the coordinate dependent diffusion method. We show that allowance for the drift component in the coordinate dependent diffusion method provides a better DP agreement with literary data. Both methods suggest the DP tendency to grow at the heterostructure boundary and to decline closer to the main p–n junction. The DP growth near the surface p–n junction the field of which is directed toward the heterostructure boundary and its decline near the main p–n junction with an oppositely directed field, as well as the observed DP growth with the electron concentration, suggest that the negatively charged VGeP complexes diffuse in the heterostructure by analogy with one-component diffusion.

Effect of Germanium Doping on the Production and Evolution of Divacancy Complexes in Neutron Irradiated Czochralski Silicon

Fourier transformed infrared absorption spectroscopy was used to investigate the effect of germanium (Ge) doping on the production and evolution of divacancy (V2) complexes in neutron irradiated Czochralski (Cz) silicon. The generation rates of V2 and vacancy–oxygen (VO) complexes were found to increase in Ge doped silicon as compared with the controlled Cz silicon, which could be ascribed to the increased availability of vacancies in Ge doped silicon arising from the temporary trapping of vacancies associated with the transient GeV pairs. Upon annealing, most of the V2 complexes were eliminated via the reaction between divacancy and self-interstitials (Sii) (V2 + Sii → V), while only 6–24% of V2 complexes were transformed into V2O complexes via the trapping of V2 complexes by interstitial oxygen (Oi), as V2 diffuses much faster than Oi. It was observed that Ge doping accelerated the V2 annihilation and in turn suppressed the transformation of V2 into V2O complexes. Those phenomena can be attributed to the increased availability of free self-interstitials in Ge doped silicon, which enhances the recombination of V2 with Sii. Additionally, an increased production of V3O complexes was observed in Ge doped silicon. The role of Ge atoms in the V3O formation was discussed in view of the two reactions V2 + VO → V3O and V2O + V → V3O.

Investigation of in-situ co-doping by Sb and P of germanium films grown on Si(001) by molecular beam epitaxy

Heavily n-type doping of Germanium was the key parameter in recent breakthroughs of Si-compatible infrared emitting devices. We investigate an in-situ co-doping technique using Phosphorus (P) and Antimony (Sb) to fabricate smooth and heavily n-type doped Ge films epitaxially grown on Si(001) using molecular beam epitaxy. The role of the rapid thermal annealing process in the dopants activation and in the significant annihilation of the threading dislocations is presented. Hall effect measurements reveal a free electron concentration of 4.2 × 1019 cm−3 at room temperature. The accumulated strain in the Ge films is studied using X-ray diffraction (XRD) data for P, Sb and co-doping, before and after annealing. A correlation between XRD and Hall effect results revealed a synergistic mechanism associated with the presence of Sb that improves the substitutional incorporation of P atoms. Atom Probe Tomography was implemented to investigate the effect of annealing on the distribution and clustering of dopants. Clustering and inhomogeneity in the density of Sb atoms are observed before annealing, while the density of P atoms was found to be homogeneous. After annealing, the clustering of P becomes more prominent. We show that the clustering is a limiting factor for the activation efficiency of Phosphorus in heavily doped Germanium. The referenced publication has been retracted by the authors because of the use of unauthorized data represented by Figs. 8, 9, 10, 11, 12, 13, and 14. These figures were obtained with the help of other scientists in IM2NP Laboratory (Marseille, France) and have been only authorized for publication in the Ph.D. thesis of M. A. Zrir. The authors recognize that the publication of data that have been obtained with substantial help from other scientists can only be with their prior authorization. The authors sincerely apologize for this and recognize that the use of unauthorized data does not comply with the ethical standards of AIP Publishing and Journal of Applied Physics.

Mixed Sn-Ge Perovskite for Enhanced Perovskite Solar Cell Performance in Air.

Lead-based perovskite solar cells have gained ground in recent years, showing efficiency as high as 20%, which is on par with that of silicon solar cells. However, the toxicity of lead makes it a nonideal candidate for use in solar cells. Alternatively, tin-based perovskites have been proposed because of their nontoxic nature and abundance. Unfortunately, these solar cells suffer from low efficiency and stability. Here, we propose a new type of perovskite material based on mixed tin and germanium. The material showed a band gap around 1.4-1.5 eV as measured from photoacoustic spectroscopy, which is ideal from the perspective of solar cells. In a solar cell device with inverted planar structure, pure tin perovskite solar cell showed a moderate efficiency of 3.31%. With 5% doping of germanium into the perovskite, the efficiency improved up to 4.48% (6.90% after 72 h) when measured in air without encapsulation.

Optimization of microstructured fibers with germanium-doped core for broad normal dispersion range

We have numerically studied different designs of technologically feasible microstructured fibers with a germanium-doped core in order to obtain normal dispersion reaching possibly far in the mid infrared. Hexagonal, Kagome and the combination of both geometries were numerically examined with respect to different constructional parameters like pitch distance, filling factor of air holes, number of layers surrounding the core, and level of germanium doping in the core. Our analysis showed that the broadest range of normal dispersion reaching 2.81 μm, while keeping an effective mode area smaller than 30 μm2, was achieved for a hexagonal lattice and a 40 mol% GeO2 doped core. The proposed fibers designs can be used in generation of a normal dispersion supercontinuum reaching the mid-IR region.

Properties of GaN-based nanopillar-shaped crystals grown on a multicrystalline Si substrate

The growth of gallium nitride-based nanopillar-shaped crystals on the multicrystalline silicon substrate that is widely employed in solar cells is presented here for the first time. The nanopillar-shaped crystals are successfully grown on the multicrystalline substrate in a manner similar to the structures grown on other substrates. Structural variations and a highly enhanced band edge emission in the photoluminescence spectrum have been observed using germanium doping.

First-principles study of optical properties of germanium doped with phosphorus and bismuth

Using first-principles calculations based on density functional theory, we investigate the electronic structures and optical properties of germanium doped by phosphorus and bismuth with different concentrations. By analyzing the electronic structures and optical properties of the doped systems, we can theoretically analyze and predict the optical and electrical practical applications of N-doped germanium semiconductors. By analyzing and comparing the densities of electronic states before and after doped, we can draw some conclusions. The conclusions show that the Fermi level moves in the direction of conduction band after being doped. Although germanium is an indirect band gap luminescent material, the doped systems all become direct band gap luminescence. Doping more or less affects various optical properties in different energy ranges. In a low energy range, the dielectric function and refractive index of the doped systems are affected. When the doping concentration is 2.083%, the dielectric function and refractive index of the doped system both have a special change. And the absorption of the doped system is changed in the high energy. As the energy increases after the absorption peak, the absorption of the doped system drops faster. The reflectance of the doped system is affected in all the energy ranges. The reflectance of the doped system increases in medium energy. And the reflectance of the doped system is reduced in low energy and high energy range. However, when the doping concentration is 2.083% and the energy is less than 1.7 eV, the reflectance of the doped system is higher than that of the undoped system. The conductivity of the doped system forms two peaks, adding a peak in low energy. The additional peaks in the systems where the doping concentrations are 1.563% and 2.083% are obvious. The peak of the loss function increases after being doped. However, as the doping concentration increases, the increment of the loss function decreases. As the doping concentration increases, the peak is formed at a higher energy. The conclusions are of significance for guiding the optical applications of N-type doped germanium. According to the conclusions, we can adjust the doping concentration and energy range in the optical applications of N-doped germanium.

Structural and optical properties of germanium-doped zinc oxide nanorods as a function of annealing temperature

ABSTRACTZinc oxide nanorods with germanium doping were prepared by ion implantation and annealing treatment method, the microstructural and optical properties of which were studied by means of the X-ray diffraction, photoluminescence, and transmission electron microscopy measurements. The pristine sample exhibited a remarkable ultraviolet emission owing to the band edge emission from the zinc oxide matrix, indicated a good crystalline quality. Three emission peaks appeared after germanium ions were doped into zinc oxide nanorods. The 513 nm photoluminescence peak was ascribed to the transition between the vacancy defect in zinc oxide matrix. Photoluminescence peaks located at 548 and 778 nm were ascribed to germanium ions luminescence center in zinc germanate grain and germanium monoxide luminescence center. The light emission tuning was obtained by germanium doping and annealing treatment, which may help the development of the practical optoelectronic devices based on zinc oxide nanomaterials.

Diffusion doping of germanium by sputtered antimony sources

Antimony sputter deposition and subsequent diffusion annealing in controlled atmosphere was implemented on Ge wafers, for achieving an optimized n+ doping aimed at the final application of these doped contacts to Ge-based radiation detectors. Two approaches were adopted for n+ doping: diffusion from Sb source sputtered directly on the Ge surface, and diffusion from a remote dopant source. Surface morphology was specifically investigated by electron (SEM-EDS) and atomic (AFM) microscopies. Diffusion profiles were characterized by Secondary Ion Mass Spectrometry (SIMS). The remote doping, obtained by using a Sb-coated Si wafer placed close to the Ge substrate during the diffusion annealing, allowed to attain defect-free surface morphologies and diffusion profiles compatible with well assessed equilibrium diffusion models.

Improved electron transfer of TiO2 based dye sensitized solar cells using Ge as sintering aid

Low electron mobility of TiO2 semi-conductor and inferior inter-particle contact facilitate recombination reactions that leads to low performance of dye sensitized solar cells (DSSCs). To improve electron mobility at relatively low sintering temperatures, doping of germanium (Ge) nanoparticles with TiO2 have been trailed due to its excellent optoelectronic and low temperature sintering properties. Anatase TiO2-Ge nanocomposites have been prepared by using colloidal suspension process and deposited on conducting glass using doctor blade technique. Four types of nanocomposites i.e. (1) TiO2–0.5wt%Ge, (2) TiO2–2wt%Ge, (3) TiO2–5wt%Ge and (4) TiO2–10wt%Ge have been prepared and sintered at 400°C with a control specimen fabricated using pure TiO2 nanoparticles (sintered at 450°C) for comparison purpose. To investigate the morphological and structural characteristics, SEM and XRD have been employed. The UV-vis and impedance spectroscopy have been performed to observe light absorption and electron transfer characteristics respectively. Finally, specimens were tested for their photo conversion efficiency. An increase in electron transfer ability and conversion efficiency have been recorded with increase in Ge nanoparticles even at 400°C sinter temperature compared to reference TiO2 photoanodessintered at 450°C.

The electrical properties and distribution of indium in germanium crystals

Indium doped germanium crystals were grown in a hydrogen atmosphere using the Czochralski method. The electrical properties of indium doped germanium crystals were measured by Hall effect at 77K. The axial and radial distributions of indium in the germanium crystals were investigated. The effective segregation coefficient of indium in germanium is determined to be 0.0009 with the concentration of indium from 3 × 1012~1 × 1019cm−3. The interface shape between melt and crystal determined the radial distribution of indium in germanium crystals.