Ge Ions Research Articles

Atomistic simulation of Na2Ti3O7: Defects, dopants, and diffusion properties

Na2Ti3O7 exhibits promise as a safe battery material for Na-ion batteries, currently undergoing extensive research. The atomistic simulation method is employed to scrutinize defects, dopant energies, and Na-ion migration in Na2Ti3O7. Notably, the Na-Frankel energy is the lowest, and the Na-anti-site cluster energy is lower than the Na-anti-site isolated energy. The migration of Na ions is observed to predominantly occur along the ab plane, where the activation energy is measured at 0.23 eV. K and Ge ions are identified as the most suitable isovalent and tetravalent dopants for Na and Ti sites, respectively. Furthermore, the introduction of the aliovalent dopant Al3+ ion on the Ti site can form additional Na+ ions. The electronic structures of the most favorable doped configurations are discussed.

Epitaxial Group-IV Quantum Dots as Room-Temperature Light Emitters

Next-generation Si-based applications ranging from short-range (quantum) data transfer to sensing could highly benefit from potential progress in group-IV-based telecom light emitters that can be readily implemented with Si Photonics components [1]. However, since Si is known to be an indirect band gap semiconductor, light emission is limited and inhibits the integration of efficient emitters, such as, e.g. light-emitting diodes and lasers on Si Photonic platforms.In this presentation, we stress that a particular type of epitaxial Ge on Si quantum dots allows for overcoming the indirect bandgap limitations of Si and Ge and, thus, enables pronounced light emission even at room temperature and above [2]. These nanostructures consist of ~2 nm high Ge-rich quantum dots on Si(001) substrate epitaxially created via strain-driven formation. However, in contrast to commonly used nanostructures, we intentionally incorporate point defects into these nanostructures during their growth through in-situ low-energy Ge ion implantation [3-4]. Therefore, the point defects can be confined within the 2 nm thick Ge layer while the surrounding Si matrix remains perfectly crystalline. We will discuss the superior light-emission properties of these so-called defect-enhanced quantum dots (DEQDs) and present the current theoretical understanding of the defect’s effects on the band structure. The latter leads to the enhanced light emission from DEQDs and the opening of direct recombination channels in k-space [5,6].In addition to signs for optically pumped lasing from DEQDs embedded in microdisk resonators, implementing these emitters into the i-region of p-i-n diodes is remarkably straightforward since the matrix material is crystalline Si [7,8]. To showcase the superior properties of these zero-dimensional light emitters, we highlight light emission from DEQD light-emitting diodes with exceptional temperature stability up to 100°C [9]. This behavior starkly contrasts conventional Si/Ge light emitters, for which the light emission is typically confined to cryogenic temperatures.For optimizing the light emission from this interlaced defect/nanostructure complex [10], we elaborate on the testing of crucial parameters related to the temperature stability of the DEQDs [8,11], the scalability of light emission with increasing the density of the DEQDs [12] and passivation of detrimental defects in the Si matrix [13].[1] I. A. Fischer, et al., APL Photonics 7, 050901 (2022).[2 ] M. Brehm, Silicon Photonics IV, 67-103, Silicon Photonics IV: Innovative Frontiers, edited by David J. Lockwood and Lorenzo Pavesi, Springer series Topics in Applied Physics (2021).[3] M. Grydlik, et al., Nano Lett. 16, 6802–6807 (2016).[4] M. Grydlik, et al., ACS Photonics 3, 298–303 (2016).[5] F. Murphy-Armando, et al., Physical Review B 103 (8), 085310 (2021).[6] M. Brehm, et al., to be published[7] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).[8] L. Spindlberger et al., Crystals 10, 351 (2020).[9] P. Rauter et al., ACS Photonics 5, 431-438 (2018).[10] M. Brehm and M. Grydlik, Nanotechnology 28, 392001 (2017).[11] L. Spindlberger et al., Physica Status Solidi (a) 216, 1900307 (2019).[12] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).[13] L. Spindlberger et al., Appl. Phys. Lett. 118, 083104 (2021).

Analysis of the extreme ultraviolet broadband spectral characteristics and spatiotemporal evolution of laser-produced germanium plasmas

This paper presents comprehensive spectral measurements and a theoretical analysis of laser-produced germanium (Ge) plasma within the 7.5–17 nm wavelength range, with the measurements being performed using spatiotemporally-resolved emission spectroscopy. We obtained and analyzed the extreme ultraviolet (EUV) spectra and their variations meticulously at various positions adjacent to the target surface. The 3p and 3d excitations of Ge ions spanning from Ge4+ to Ge13+ were calculated using the Cowan configuration interaction codes, with particular emphasis being placed on analysis of the spectral line distributions in the 3d-np, 3d-nf, and 3p-3d, 4s, 4d transition arrays. This analysis indicated the contributions made by these transition arrays to the broadband spectral features that were observed experimentally. By using a steady-state collisional radiation model along with a normalized Boltzmann distribution assumption, we clarified the predominant contributions of the 3d-4p and 3p-3d transitions from the Ge7+ to Ge9+ ions in close proximity to the target surface, along with those from the Ge5+ and Ge6+ ions at greater distances. Furthermore, by combining the results above with a plasma dynamics evolution analysis, we gained insights into how the plasma's transient and nonuniform properties influence the analysis of complex EUV band spectral profiles and examine their implications for spectral diagnostics. These results will be useful for plasma spectral diagnosis and for application to development of pulsed short-wavelength light sources.

Study on Single Event Effects of Enhanced GaN HEMT Devices under Various Conditions.

GaN HEMT devices are sensitive to the single event effect (SEE) caused by heavy ions, and their reliability affects the safe use of space equipment. In this work, a Ge ion (LET = 37 MeV·cm2/mg) and Bi ion (LET = 98 MeV·cm2/mg) were used to irradiate Cascode GaN power devices by heavy ion accelerator experimental device. The differences of SEE under three conditions: pre-applied electrical stress, different LET values, and gate voltages are studied, and the related damage mechanism is discussed. The experimental results show that the pre-application of electrical stress before radiation leads to an electron de-trapping effect, generating defects within the GaN device. These defects will assist in charge collection so that the drain leakage current of the device will be enhanced. The higher the LET value, the more electron-hole pairs are ionized. Therefore, the charge collected by the drain increases, and the burn-out voltage advances. In the off state, the more negative the gate voltage, the higher the drain voltage of the GaN HEMT device, and the more serious the back-channel effect. This study provides an important theoretical basis for the reliability of GaN power devices in radiation environments.

Measurement of the Isolated Nuclear Two-Photon Decay in ^{72}Ge.

The nuclear two-photon or double-gamma (2γ) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the 2γ decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to ∼100 keV and half-lives as short as ∼10 ms. The half-life for the 2γ decay of the first-excited 0^{+} state in bare ^{72}Ge ions was determined to be 23.9(6)ms, which strongly deviates from expectations.

Light emission from ion-implanted SiGe quantum dots grown on Si substrates

We report on electroluminescence spectroscopy experiments demonstrating room-temperature light emission from heavily alloyed SiGe quantum dots, for which the light emission properties are enhanced by incorporated split-[110] self-interstitials. The quantum dots are formed during molecular beam epitaxy deposition of Si0.6Ge0.4 alloys on n-doped silicon-on-insulator substrates. To create the split-[110] self-interstitials the quantum dots were co-implantated in-situ using Si and Ge ions. The hybrid emitters were further embedded into the intrinsic region of a p-i-n diode structure to enable electrical pumping. Similar to previous theoretical results on unstrained Ge-based quantum dots containing these defects, radiative direct transitions are possible for these SiGe light emitters. However, in SiGe dots these transitions are not at the Brillouin zone center. Instead, first-principles calculations indicate that the presence of the split-[110] self-interstitial defect in strained and unstrained SiGe can lead to optically direct transitions in momentum space in the X-direction of the Brillouin zone.

The optimized size distribution and NIR persistent luminescence of Zn2Ga2.98-4x/3HfxGe0.75O8:Cr0.02 nanoparticles via high-valence ion doping

In this study, spinel-phase Zn2Ga4-4y/3GeyO8 (ZGO:Ge4+y) (y = 0–0.90) and Zn2Ga2.98-4x/3HfxGe0.75O8:Cr0.02 (ZGGO:Cr3+,Hf4+x) (x = 0–0.075) nanoparticles were prepared by a hydrothermal method combined with a subsequent vacuum annealing. For Cr3+doped ZGO:Ge4+y nanoparticles, it was found that the replacement of Ga3+ with high-valence Ge4+ can lead to more uniform morphology and enhanced afterglow. Meanwhile, for ZGGO:Cr3+,Hf4+x nanoparticles, the non-equivalent replacement of Ga3+ with high-valence Hf4+ can give rise to the decrease in standard deviation gradually from 12.3 to 7.0 nm and the afterglow intensity is increased to 3.4 times of the undoped ZGGO:Cr3+ nanoparticles. Based on the first principle calculations using an ideal model of Zn8Ga16O32 (ZGO) unit, it is found that the formation energy (11.32 eV) using a doped model of Zn8Ga12Ge3O32 unit (i.e. three Ge ions substitute for three Ga ions and one Ga vacancy (VGa′′′) is created in a unit due to the charge compensation effect) is lower than that (13.35 eV) using a doped model of Zn11Ga10Ge3O32 unit (i.e. three Ge ions and three Zn ions substitute for six Ga ions without the charge compensation effect). Combined with the spectral data, we can confirm that, in the case of the same Ge doping concentration (y = 0.75), the formula of ZGGO host is Zn2Ga4-4y/3GeyO8 rather than Zn2+yGa4-2yGeyO8. Based on the above ZGGO (Zn8Ga12Ge3O32) model, it is found that the smaller formation energies (−1.49 to −3.34 eV) of the Hf4+ doped systems further prove that high-valence Hf4+ ions prefer to substitute for octahedral and tetrahedral Ga3+ and Ge4+ sites and promote the creation of Zn’Ga–Ga°Zn and Ga°Zn defects and it leads to the improved afterglow. Furthermore, contrary to other isovalent ions (such as Nd3+) doped ZGGO nanoparticles, ZGGO:Cr3+,Hf4+x nanoparticles exhibit excellent dispersion stability in an acidic fluid. These findings suggest ZGGO:Cr3+,Hf4+x nanoparticles might be potential for bioimaging in an acidic body fluid.

The luminescence study of GeV centers and damage in diamond induced by 300keV Ge ion implantation

In this paper, the germanium-vacancy (GeV) in diamond produced by 300 keV Ge ion implantation and subsequent annealing, were investigated by Raman spectroscopy and photoluminescence (PL) spectroscopy, and meanwhile the different ion injection models were given by the Stopping and the Rang of Ions in Matter (SRIM) simulation. Results showed that the Raman peak of diamond shifted to the lower wavenumber after Ge ion implantation, indicating the ion implantation caused amorphous graphitization in the crystal that generated the local tensile stress. Most of the amorphous graphitization was eliminated at an annealing temperature of 300–700 °C by evidence of the variation of ID/IG value. When the annealing temperature was higher than 700 °C, the vacancy migrate a longer distance to find Ge ions, then convert Ge ions into GeV centers, and thus an interesting zero phonon line (ZPL) at 602.8 nm appeared which was associated with GeV center.

Effect of Mn Substitution on GeFe2O4 as an Anode for Sodium Ion Batteries

GeFe2O4 (GFO), with its intriguing intercalation mechanism based on alloying–conversion reactions, was recently proposed as an anode material for sodium ion batteries (SIBs). However, drawbacks related to excessive volume expansion during intercalation/deintercalation and poor electronic conductivity enormously hinder its practical application in batteries. In this regard, some experimental strategies such as cation substitutions and proper architectures/carbon coatings can be adopted. In this paper, pure and Mn-doped GFO samples were prepared by hydrothermal synthesis. The doped samples maintained the spinel cubic structure and the morphology of pure GFO. The electrochemical tests of the samples, performed after proper carbon coating, showed the expected redox processes involving both Ge and Fe ions. The Mn doping had a positive effect on the capacity values at a low current density (about 350 mAh/g at C/5 for the Mn 5% doping in comparison to 300 mAh/g for the pure sample). Concerning the cycling stability, the doped samples were able to provide 129 mAh/g (Mn 10%) and 150 mAh/g (Mn 5%) at C/10 after 60 cycles.

Prediction of heavy metal ion distribution and Pb and Zn ion concentrations in the tailing pond area.

The pollution caused by tailings ponds has resulted in ecological damage, with soil contamination significantly impacting the daily lives of residents in the vicinity of mining areas and the future development of mining areas. This study assesses the transport status of heavy metal pollution in tailings areas and predicts its impact on future pollution levels. This study focused on lead-zinc tailing ponds, exploring the spatial and chemical distribution characteristics of heavy metals based on the distributions of Pb, Zn, As, Cu, Cr, Cd, Hg, and Ge ions. The concentrations of the major heavy metal ions Pb and Zn in tailings ponds were predicted via the exponential smoothing method. ① The total accumulation of Pb and Zn in the mine tailings ranges from 936.74~1212.61 mg/kg and 1611.85~2191.47 mg/kg, much greater than the total accumulation of the remaining six heavy metals. The total accumulation of associated heavy metal Cu was high, and the lowest total heavy metals were Hg and Ge at only 0.19 mg/kg and 1.05 mg/kg. ② The analyses of soil heavy metal chemical forms reveal that the heavy metals Pb and Zn had the highest exchangeable state content and state ratio and the strongest transport activity in the industrial plaza and village soils. Pb and Zn are the heavy metals with the greatest eco-environmental impacts in the mining area. ③ The predicted results show that the soil concentrations of the heavy metals Pb and Zn around the tailings area in 2026 are 1.335 and 1.191 times the predicted time starting values. The concentrations of the heavy metals Pb and Zn at the starting point of the forecast are already 3.34 and 3.02 times the upper limits of the environmental standard (according to environmental standards for gravelly grey calcium soils). These results have significant implications for heavy metal pollution risk management.

Heavy ion single event effect in double-trench SiC metal–oxide–semiconductor field-effect transistors

In this paper, experiments on 208 MeV Ge ion irradiation with different source-drain bias voltages are carried out for the double-trench SiC metal–oxide–semiconductor field-effect transistors, and the physical mechanism of the single event effect is analyzed. The experimental results show that the drain leakage current of the device increases more obviously with the increase of the initial bias voltage during irradiation. When the bias voltage is 400 V during irradiation, the device has a single event burned at a fluence of 9×10<sup>4</sup> ion/cm<sup>2</sup>, and when the bias voltage is 500 V, the device has a single event burned at a fluence of 3×10<sup>4</sup> ion/cm<sup>2</sup>, so when the LET value is 37.3 MeV·cm<sup>2</sup>/mg, the SEB threshold of DUT does not exceed 400 V, which is lower than 34 % of the rated operational voltage. The post gate-characteristics test results show that the leakage current of the device with a bias voltage of 100 V does not change significantly during irradiation. When the bias voltage is 200 V, the gate leakage and the drain leakage of the device both increase, so do they when the bias voltage is 300 V, which is positively related to bias voltage. In order to further analyze the single particle effect mechanism of device, the simulation is conducted by using TCAD tool. The simulation results show that at low bias voltage, the heavy ion incident device generates electron-hole pairs, the electrons are quickly swept out, and the holes accumulate at the gate oxygen corner under the effect of the electric field, which combines the source-drain bias voltage, leading to the formation of leakage current channels in the gate oxygen layer. The simulation results also show that at high bias voltage, the electrons generated by the incident heavy ion move towards the junction of the N<sup>–</sup> drift layer and the N<sup>+</sup> substrate under the effect of the electric field, which further increases the electric field strength and causes significant impact ionization. The local high current density generated by the impact ionization and the load large electric field causes the lattice temperature to exceed the melting point of silicon carbide, causing single event burnout. This work provides a reference and support for studying the radiation effect mechanism and putting silicon carbide power devices into aerospace applications.

Impact of Various Dopants on Thermoelectric Transport Properties of Polycrystalline GeSb2Te4

GeSb2Te4 (GST124), one of the well‐known phase‐change materials for nonvolatile memory and rewritable optical storage, has been recently found to be promising thermoelectric materials with low lattice thermal conductivity and high electrical conductivity. However, its thermoelectric performance is greatly restricted by the excessively high hole concentration. Herein, the impact of a series of group IIIA (Al, Ga, In) and group VIA (S, Se) dopants on the electrical transport properties of polycrystalline GST124 has been studied. It is found that element sulfur (S) has the best doping efficiency because the GeS bonds are very strong and ionic that are beneficial for suppressing Ge vacancies to reduce the carrier concentration. Meanwhile, element indium (In) also shows decent doping efficiency because its ionic radius is close to the Ge ion and the InTe bonds have moderate bonding strength. Moreover, In doping introduces a resonant level in the valence band, leading to enhanced Seebeck coefficient and power factor. A high figure of merit (zT)of 0.73 at 700 K and an average zT of 0.48 over 300–750 K are obtained in Ge0.92In0.08Sb2Te4, which are 26% and 66% higher than pristine GST124. This study will advance the understanding and development of high‐performance GeSbTe‐based thermoelectric materials.

Doping of large amount tetravalent Ge ions into Fe2O3 structure and experimental results on modified structural, optical and electronic properties

We report the doping of high concentration of tetravalent Ge4+ ions (5 mol % for x = 0.05–30 mol % for x = 0.30) at the Fe3+ sites of Fe2-xGexO3 system by chemical coprecipitation route. The charge state of Fe and Ge ions has been modified into lower values, in addition to their normal +3 and + 4 states, to stabilize the rhombohedral phase of hematite (α-Fe2O3) structure. X-ray photoelectron spectra and optical band gap measurements indicated a combination of ionic and covalence character of metal-oxygen bonds as an effect of Ge doping in the hematite structure. The Ge doped hematite samples have exhibited semiconductor properties with band gap of 1.50–4.70 eV and remarkably enhanced electrical conductivity (σ ∼ 10−4 S/m) in comparison to α-Fe2O3 (10−11 S/m). The results confirmed the strategy of enhancing electrical conductivity in hematite structure by doping of tetravalent cations. The thermo-conductivity measurements using warming and cooling modes showed highly irreversible feature at higher temperatures. Some of the samples indicated metal-like state at lower temperature, in addition to semiconductor state at higher temperatures. It has been understood that combination of ionic and covalence character of the metal-oxygen bonds has played an important role in modifying the semiconductor properties in Ge doped Fe2O3 system.

Synthesis of novel MOF for adsorption of germanium: Kinetics, isotherm and thermodynamics

As a semiconductor material, effective recycle and utilization of germanium is an important research direction. In this paper, an efficient adsorbent for recovery of germanium is prepared by grafting D-anhydrous glucose onto UiO-66-NH2 (DG-UiO-66). The successful preparation of adsorbent is demonstrated through a series of characterizations. Under the optimum experimental conditions (298 K, pH = 10), the maximum adsorption capacity of germanium by DG-UiO-66 is 216.86 mg/g. The adsorption behavior of Ge(IV) on the adsorbent is analyzed, and the adsorption of Ge(IV) conform to the pseudo-secondary kinetic model and Langmuir isotherm model, and the adsorption mechanism of germanium is further analyzed by intraparticle diffusion model. The thermodynamic results show that the higher the temperature, the stronger the adsorption capacity of Ge(IV), and the reaction is spontaneous. The adsorbent has good anionic anti-interference ability, and the adsorption efficiency can still reach more than 80% after repeated adsorption for five times. DG-UiO-66 is an excellent Ge(IV) ion adsorbent with higher germanium adsorption effect than previous adsorbents.

Germanium/niobium/polyetherketoneketone ternary biocomposite with crisscross micro-nano patterns created by femtosecond laser for enhancing bone-bonding and resisting infection

Loosening and infection are two main reasons for the failure of orthopedic implants. Bone-bonding strengthens the fixation/stability of implants with host bone that extends its service life. Herein, a germanium (Ge)/niobium (Nb)/polyetherketoneketone (PEKK) ternary composite (GNP) was fabricated by melting blend, and crisscross micro-nano patterns on GNP (GNPF) were created by femtosecond laser. The results displayed compared with PEKK and GNP, GNPF with micro-nano patterns displayed remarkable upgradation in surface properties with higher roughness and hydrophilicity/surface energy, etc. GNPF not only promoted osteoblast differentiation but also encouraged the M2 macrophage polarization in vitro. Moreover, GNPF inhibited the bacteria reproduction in vitro, and resisted infection in vivo owing to the sustained release of Ge ion. Further, GNPF remarkably facilitated bone-formation and bone-bonding by inhibiting fibrous capsules in vivo. The mechanism for enhancements of osteoblast response and M2 macrophage polarization in vitro, and bone-bonding in vivo for GNPF was attributed to the cooperative effect of the micro-nano patterns and sustained release of Ge/Nb ions. Consequently, GNPF with osteogenic, anti-inflammatory, and anti-bacterial functions boosted bone-bonding and resisted infection, thereby displaying a promising potential for construction of segmental bone defects.

Liquid Nitrogen Temperature Mechanoluminescence and Persistent Luminescence

AbstractAs novel stress‐sensing materials, the reported mechanoluminescence (ML) phosphors work only at or above room temperature. Herein, the ML response to low temperatures (77 K) is extended by employing ultra‐shallow traps. Strong ML stimulated by handwriting force followed by persistent luminescence is observed in BaSi2O2N2:Eu2+ (BSON) at 77 K. The UV pre‐irradiated BSON can still keep the characteristics of ML with 45% intensity after 300 min. Abundant ultra‐shallow traps with depth of ≈0.19 eV are found and revealed to be responsible for the low‐temperature ML and persistent luminescence. Manipulation of the ultra‐shallow traps is realized by doping Ge, Er, and Ce ions in BSON, leading to significant ML enhancement at 77 K. Together with ML, the ultra‐shallow traps also exhibit force memory ability to replicate the pre‐applied force pattern simply by afterglow. The finding advances the state‐of‐the‐art in force sensing under low temperature conditions.

Cathode Nanophosphors

High-current cathodic pulses on an aluminum electrode in solutions containing sufficiently high concentrations of Mg, Ca, Sr, Al, Sc, Y, or La nitrates in a mixture with H3BO3, HF, H3PO4, or H4P2O7 are accompanied by an intense intrinsic luminescence of a number of heavy metals, the ions of which are captured by salt nanofilms and luminescence under the action of hot electrons when are in an environment characteristic of crystal phosphors. The effect of the cathode nanophosphor (CNP) was found in more than 100 systems; photographs are presented for most of the systems. Ga, In, Tl, Ge, Sn, Pb, Mn, Cu, Ag, Cd, Ce, Tb, and Zr ions were activators. The effect of matrix composition on the spectral and kinetic characteristics of the CNP was shown on several examples; a qualitative description of the phenomenon is given, and the prospects for its application to chemical analysis are considered.

Bright single-photon emission from a GeV center in diamond under a microfabricated solid immersion lens at room temperature

We report on the metrological characterization of the emission from a germanium-vacancy center in diamond under a microfabricated solid immersion lens in a confocal laser-scanning microscope setup. Ge ions were implanted into a synthetic diamond at 3 MeV, and germanium-vacancy centers were then formed by subsequent annealing. Afterward, solid immersion lenses were fabricated in a focused ion beam scanning electron microscope. The photoluminescence was investigated at room temperature in terms of the spectral distribution, the excited state lifetime, the second-order correlation function, and the saturation behavior, proving simultaneous high single-photon purity and high brightness. Two methods were exploited to minimize the residual multi-photon probability: spectral filtering and temporal filtering. According to these results, we assume that Raman scattered photons and emission from neighboring color centers play an important role in the residual multi-photon emission probability. The system efficiency of the single-photon source was investigated and found to be in accordance with the value calculated from all sources of loss in the setup. The branching ratio of the germanium-vacancy center for the decay into the ground state and into metastable state was calculated. The results enable the usage of the single-photon source in future quantum radiometric experiments.

Near infrared photoluminescence of Si1–xGex quantum dots fabricated by double hot Ge+/Si+ implantation into SiO2 layer

In this study, we developed very simple and ULSI (ultra large scale integration) compatible fabrication processes for group-IV (Si1–xGex and Si) semiconductor quantum dots (QDs) to apply hybrid ULSIs with photonic and electron devices, using double Ge+/Si+ hot-ion implantation into a SiO2 layer with larger bandgap EG and the post-furnace annealing. We successfully demonstrated the near-infrared (IR) photoluminescence (PL) from Si1–xGex-QDs. Transmission electron microscopy observations of single-crystallized Si1–xGex-QDs revealed that the diameter and the QD density were 3.6 ± 0.9 nm and (2.6 ± 0.4) × 1012 cm−2, respectively. In addition, Ge atoms were detected in the Si1–xGex-QDs by the energy dispersive x-ray spectroscopy analysis, and the Ge fraction of Si1–xGex-QDs was varied from 0.06 to 0.26 by changing the Ge ion dose. The increase in the PL intensity by forming gas annealing was attributed to the dangling-bond reduction by the H-atom termination method. The PL spectrum of Si1–xGex-QDs was fitted by PL components of two QD structures containing Si1–xGex and Si materials. The PL intensity and PL-peak photon energy of Si1–xGex-QDs strongly depended on the Ge fraction. The Si1–xGex-QDs achieved the maximum PL intensity at x ≈ 0.13. High PL-peak photon energy (∼1.31 eV) of Si1–xGex-QDs is attributed to the quantum confinement effect of carriers in QDs. Consequently, group-IV semiconductor QDs including Si1–xGex, Si, SiC, and C, through the simple hot-ion implantation into the SiO2 layer, exhibited a wide range of PL emissions from the near-IR to ultraviolet regions.

Formation of crystalline Si1-xGex top layers by ion implantation in crystalline silicon

Semiconductor nanocrystals incorporated in a dielectric film are widely studied as potential candidates to exceed the Shockley-Queisser theoretical conversion limit of photovoltaic cells. In this context, Ge nanocrystals embedded in SiO2 films seem to be among the best candidates. However, the charges generated in the dielectric film are hard to collect. For this reason, it would be better if the charges were generated in a semiconductor matrix such as silicon, which has better conductivity. However, implanted Ge atoms have poor mobility in a silicon matrix and thus Ge nanocrystals formation is not likely. But even if the formation of Ge nanocrystals seems difficult, it would still be interesting to form crystalline Si1-xGex alloys. This work investigates the formation of the Si1-xGex films by ion implantation and their crystallinity. 36 keV Ge ions were implanted in crystalline Si substrates, with fluences ranging from 5 × 1015 to 1.5 × 1017 Ge/cm2 at temperatures up to 600 °C. Rutherford Backscattering Spectrometry (RBS), Raman Spectroscopy, and Transmission Electron Microscopy (TEM) were used to investigate the microstructure of the Si1-xGex alloys. It is shown that germanium is mostly incorporated in the crystal network in substitutional sites. XRD, Raman spectroscopy, and TEM confirm that the Si1-xGex layer on top of the c-Si substrate is monocrystalline. TEM also indicates the possible presence of nanostructures, extended defects or both. Implantation was also carried out at temperatures up to 600 °C, with the objective of preserving the crystallinity and promoting Ge diffusion into nanoclusters. RBS shows that the Ge profile is more extended in depth for the sample implanted at 600 °C, compared to a room temperature implantation. As the energy of the ions is the same in both samples, this indicates that Ge is able to diffuse in depth during the implantation at 600 °C compared to implantation at ambient temperature. However, RBS/C shows that the minimal yield is higher for the implantation at 600 °C, indicating a high concentration of interstitials or that crystallinity is deteriorated, as confirmed by TEM.