Low Sn Content Research Articles

Material gain engineering in GeSn/Ge quantum wells integrated with an Si platform.

It is shown that compressively strained Ge1−xSnx/Ge quantum wells (QWs) grown on a Ge substrate with 0.1 ≤ x ≤ 0.2 and width of 8 nm ≤ d ≤ 14 nm are a very promising gain medium for lasers integrated with an Si platform. Such QWs are type-I QWs with a direct bandgap and positive transverse electric mode of material gain, i.e. the modal gain. The electronic band structure near the center of Brillouin zone has been calculated for various Ge1−xSnx/Ge QWs with use of the 8-band kp Hamiltonian. To calculate the material gain for these QWs, occupation of the L valley in Ge barriers has been taken into account. It is clearly shown that this occupation has a lot of influence on the material gain in the QWs with low Sn concentrations (Sn < 15%) and is less important for QWs with larger Sn concentration (Sn > 15%). However, for QWs with Sn > 20% the critical thickness of a GeSn layer deposited on a Ge substrate starts to play an important role. Reduction in the QW width shifts up the ground electron subband in the QW and increases occupation of the L valley in the barriers instead of the Γ valley in the QW region.

Surface analysis of epitaxially grown GeSn alloys with Sn contents between 15% and 18%

Metastable Germanium–tin (GeSn) layers with rather high Sn content between 15% and 18% grown on Si substrates by molecular beam epitaxy were analyzed for the morphological changes on a surface before and after reaching critical layer parameters (thickness, Sn content, and growth temperature) for surface roughening. Atomic-force microscopy investigations were performed as a function of thickness and separately for varying Sn concentrations in the GeSn layer. Epitaxial growth of metastable, uniform GeSn (15% Sn content) layers is obtained up to a critical thickness which increases from about 80 to above 200 nm by reducing the nominal growth temperature from 160 to 140 °C. Phase separation of the complete layer into tin-rich surface protrusions and a Ge-rich matrix takes place beyond the critical thickness. This surface roughening via phase separation was not observed in earlier investigations with lower Sn concentrations (<6%). Tin depletion in the GeSn matrix was confirmed by using energy-dispersive X-ray spectroscopy measurements showing residual Sn concentration below 5%. Additionally, creation of droplets with high concentration of tin on the surfaces was confirmed by energy-dispersive X-ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.

Low-Temperature Formation of Sn-Doped Ge on Insulating Substrates by Metal-Induced Crystallization

Low-temperature formation of Sn-doped Ge on insulator is desired to realize next generation flexible electronics. To achieve this, metal-induced crystallization (MIC) of a-GeSn is investigated. By MIC of a-GeSn with initial Sn concentration of 5%, Sn-doped Ge is obtained at low temperatures (<250℃). The Sn concentration (0.5-2.0%) in the grown layers can be controlled by modulating the annealing temperatures in the range of 150-250℃. Introduction A technique for low-temperature (≤250°C) formation of high-quality crystalline Ge films on insulator is expected to realize advanced high performance thin film transistors (TFT) on flexible plastic substrates (softening temperature: ~300oC). To improve quality of Ge crystals, Sn-doping (<4%) is very effective, because it enables passivation of point defects in Ge [1]. This triggered the recent research of solid-phase crystallization of Sn-doped Ge (Sn concentration: 2%) on SiO2layers [2]. However, the growth temperature (425°C) reported to date is higher than the softening temperatures of plastic substrates. To decrease the growth temperature of Sn-doped Ge, in the present study, we investigate metal-induced crystallization (MIC) of a-GeSn. This successfully decreases the growth temperature below 250°C. Experimental Procedure Fig.1 schematically shows the procedure of sample preparation. Amorphous Ge1-xSnx layers (x: 0-0.2, thickness: 100 nm) were deposited on quartz substrates at room temperature. Then, Au layer patterns were formed on the amorphous GeSn layers. The samples were annealed at 150-250oC for 10-60 min to induce lateral growth in a N2ambient. The growth characteristics were analyzed by Nomarski optical microscopy and microprobe Raman spectroscopy. Results and Discussion Figs. 2(a) and 2(b) show Nomarski optical micrographs of Ge1-xSnx (x: 0.05 and 0.2, respectively) samples after annealing at 250oC for 10 min. Au pattern regions are located in the left side areas of the micrographs. In the case of the low Sn concentration (5%), different contrast regions are observed around the Au patterns, as indicated by the broken lines. On the other hand, the sample with the high Sn concentration (20%) shows no change around the Au pattern after annealing. The Raman spectra obtained from these samples are summarized in Fig. 2(c). In Raman spectra #1 for the low Sn concentration (5%), a sharp peak due to Ge-Ge bonding in c-Ge is clearly observed. On the other hand, no peaks are detected in spectra #3 for the sample with the high Sn concentration (20%). These results indicate that lateral growth is generated from the Au patterns for samples with the low Sn concentration (5%), while it is not generated for the high Sn concentration (20%).The lateral growth lengths at 150 and 250oC for samples with various Sn concentrations were estimated using theNomarski optical microscopy combined with line-scanning of microprobe Raman measurements. The results are summarized as a function of the annealing time in Fig. 3. In the case of low Sn concentrations (<5%), lateral growth lengths increase in a short annealing time (10 min). In addition, the growth lengths increase with increasing annealing temperature and exceed 20 μm at 250°C, which is sufficient for device fabrication.The substitutional Sn concentrations in grown layers for samples with the initial Sn concentration of 5% are evaluated by peak shift of Raman spectra. Substitutional Sn concentrations of 0.5−2.0% are obtained in grown layers, which is useful to passivate point defects in Ge [1]. The substitutional Sn concentration depended on the annealing temperature. This indicates that the substitutional Sn concentration can be controlled by modulating annealing temperature. This technique will be useful to realize next generation flexible electronics.

Hole Effective Mass of Strained Ge1-X Sn x Alloys P-Channel Quantum-Well MOSFETs on (001), (110), and (111) Ge Substrates

- The dependence of effective mass on Sn content, pseudomorphic strain, cap layer thickness, and substrate orientation is theoretically studied for Ge-cap/Ge1-x Sn x /Ge substrate p-channel MOSFETs through six-band k·p method. The Luttinger-like and deformation potential parameters were obtained from the fit of Ge1-x Sn x band structures by the empirical pseudopotential method (EPM). The valence band alignment is theoretically determined by the EPM and the model-solid theory. The high Sn content and thin Ge-cap layer both result the small conductivity mass along <110> of the first subband. Introduction Sn incorporating into Ge makes Ge1-x Sn x alloys as a direct band gap material that is good for nFETs.[1] For Ge1-x Sn x p-channel, several works show the high hole mobility on Ge (001)[2], (110)[3], and (111)[4] substrates. The strain effect to reduce the conductivity mass (m c) might be the main factor for the mobility enhancement.[5] However, there are few theoretical reports to address the dependence. In addition, few works discuss the m c on the Ge1-x Sn x quantum well (QW) heterostructures. In this work, the m c of Ge-cap/Ge1-x Sn x QW/Ge substrate FETs dependent with different Sn content, strain, cap thickness, and substrate orientations is theoretically studied. Models The dependence of valence band structures near the Γ point and effective mass of Ge1-x Sn x alloys along [100], [110], and [111] on Sn content and pseudomorphic strain on (001), (110), and (111) substrates are calculated by the six-band k·p model with the fitted Luttinger-like and deformation potential parameters derived from the band structure calculated by EPM[1]. Note that the fit of band structure of spin-orbital is ingnored for better fit of the other two valence bands. The EPM claculated valence band strucutres (solid line) of relxed Ge (Fig. 1(a)) and Ge0.9Sn0.1 (Fig. 1(b)) and strained Ge (Fig. 1(c)) and Ge0.9Sn0.1 (Fig. 1(d)) under (110) in-plane biaxial compressive strain of -1 % (ε|| = -1%) are compared to the band strucutres calculated by six-band k·p model (dash line). To simulate the p-channel inversion layer of Ge-cap/10 nm Ge1-x Sn x QW layer on (001), (110), and (111) Ge substrates, the six-band k·p model was used in the self-consistently calculations of Poisson and Schrödinger equations.[6] The valence band alignment of the heterostructure is theoretically determined by the EPM and the model-solid theory[7]. The inverse of m c along channel direction <110> of 1stsubband will be calculated as Ref. [6]. Results and Discussions Fig. 2(a) shows the calculated valence band diagram of 1st subband hole distribution of Ge-cap/Ge0.9Sn0.1 QW on Ge (001) substrate at N inv = 5×1012 cm-2 with cap of 4 nm and 2 nm. For the cap of 4 nm, the 1st subband energy (E 1st ) cross the cap and QW layers results the ~30% and ~70% carriers of 1st subband located at cap and QW layer, respectively. Note that the Fermi level energy is set as 0 eV. For the cap of 2 nm, there is only ~10% carriers located at cap and ~90% at QW layer. Fig. 2(b) shows the confined 2D energy contours of the 1st subband of Ge0.9Sn0.1 QW for cap of 4 nm (solid line) and 2 nm (dashed line). The larger of cap of 2 nm than that of 4 nm shows the small m c of Ge-cap/Ge0.9Sn0.1QW/Ge (001) with thin cap layer. For the Sn content up to 15 % (Fig. 2(c)), there is only ~9% and ~5% carriers located at cap layer for cap of 4 nm and 2 nm, respectively, due to the increasing valence band offset by increasing Sn content. The comparable of cap of 2 nm and 4 nm are presented in Fig. 2(d). Conclusion The m c of Ge-cap/Ge1-x Sn x /Ge substrates are theoretically studied through six-band k·p method calibrated by EPM. The m c of 1st subband is composed of the m c of the cap and QW layers due to the small valence band offset with low Sn content. High Sn content and thin cap layer keep the carriers of 1st subband located in the QW layer to result small m c. Reference [1] H.-S. Lan and C. W. Liu, Appl. Phys. Lett., 104, p. 192101, 2014. [2] Dian Lei et al., J. Appl. Phys., 119, p. 024502, 2016. [3] Chunlei Zhan et al., in Symp. VLSI Technol., Dig. Tech. Pap., 2012. [4] Yan Liu et al., Semicond. Sci. Technol., 29, p. 115027, 2014. [5] Suyog Gupta et al., I EEE Electron Device Lett., 34(7), p. 831, 2013. [6] H.-S. Lan et al., ECS Transactions, 50, p. 151-155, 2013. [7] Chris G. Van de Walle, Phys. Rev. B, 39, p. 1871, 1989. Figure 1

(Invited) Future Applications of SiGeSn and GeSn

Silicon photonics is considered to be an attractive pathway to drastically reduce power consumption in information technology based on classical Si microelectronics. Group IV alloys, namely Ge and SiGe on Si, are heavily investigated for the integration of modulators and detectors on Si [1,2]. However, higher integration levels of optical data transfer on the chip will require the integration of low power laser. The latter is approached by a wide range of technologies to deposit III/V structures on Si as well as by bonding III/V lasers Si (see ref. 3-7 in ref. [3]). Recently, a direct bandgap as well as optically pumped lasing was demonstrated for GeSn alloys deposited on Ge virtual substrates on Si (100) 8” wafers [3]. Here, efforts are reported of this ongoing endeavor towards an electrically pumped group IV laser. Moreover due to the predicted low effective mass for electrons in the Г-valley, resulting in high electron mobility as well as high carrier injection velocity, the material bears notable potential for high speed, low power circuitry. A novel epitaxial growth technology, namely, reactive gas source epitaxy has been applied to grow GeSn and SiGeSn film and heterostructures in a commercial 8” LPCVD tool, using Ge2H6, Si2H6 and SnCl4 has source gases in an N2 ambient. PH3 and B2H6 are used as sources for n- and p-type doping. Hetero- and quantum well structures containing SiGeSn/GeSn and strained Ge / GeSn layer, respectively, have been deposited at low growth temperatures (down to 325°C) and Sn concentrations up to 14.5%. Careful structural investigation were performed using X-ray diffractometry and transmission electron microscopy. Thick GeSn films grown on Ge will release about 80% of the strain. Interestingly, misfit dislocations are found typically only at the lowest interface towards the virtual Ge substrate, the interface structure within Hetero- and quantum wells structures appears to be free from extended defects. Optical pumping was performed using a ND-YAG laser with pulse duration of 5 ns. PL spectra are taken using a FTIR spectrometer equipped with a InSb detector. To improve the performance of optically pumped laser obtained from GeSn Fabry-Perot devices fabricated using simple mesa stripes [3], the GeSn mesa lines were undercut by RIE processing. This yields efficient strain relaxation in the undercut area. We have then an increase in the energy splitting between Г and L valley for electrons and a mode overlap of ~94% leading to an improved performance of these laser in comparison to the simple Fabry Perot devices previously reported [3]. These laser operate up to 135K, additionally the lasing efficiency is doubled and threshold pump power is cut by half. Similarly, micro-disc laser have been fabricated. Multi-mode lasing involving several TE and TM modes is observed up to 140K. The threshold is found at a pump power of ~225 kW/cm2. A minimum Sn concentration of ~ 8.5% is found to be required to obtain lasing in these relaxed GeSn structures. Light emitting diodes have been processed from p-i-n GeSn homojunctions. Light emission was observed up to 300K. First SiGeSn layers exhibiting a direct band gap, verified by comparing PL data and a joint density of state model are discussed. SiGeSn/GeSn p-i-n double heterostructures were grown, labelling the next milestone on the path towards an electrically pumped group IV laser. Moreover, the potential of GeSn alloys for the fabrication of low power, high frequency electronics is discussed. In particular, Bandstructure calculation reveal low effective masses, high mobilities and a high carrier injection velocity for electrons in the Gamma valley of the conduction band, making this material most interesting for the monolithic integration of optical and electronic devices. Acknowledgement The staff at PGI-9 and the clean room team at FZ-Jülich is acknowledged for their support. Special thanks to continuous input of Jeremy Witzens (RWTH) and Zoran Ikonic (Univ. Leeds) in analysing the data and modelling GeSn devices. References S. Assefa, F. Xia, F. and Y.A. Vlasov, “Reinventing germanium avalanche photodetector for nano-photonic on-chip optical interconnects. Nature 464, 80–84 (2010). Xu, Q., Schmidt, B., Pradhan, S. & Lipson, M. Micrometre-scale silicon electro-optic modulator. Nature 435, 325–327 (2005). S. Wirths, R. Geiger, N. von den Driesch, G. Mussler, T. Stoica, S. Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J. M. Hartmann, H. Sigg, J. Faist, D. Buca and D. Grützmacher, Nature Photonics 9, 88–92 (2015)

Electromodulation spectroscopy of direct optical transitions in Ge1−xSnx layers under hydrostatic pressure and built-in strain

Unstrained Ge1−xSnx layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge0.97Sn0.03 layers with built-in compressive (ε = −0.5%) and tensile (ε = 0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photoreflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge1−xSnx layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2 ± 0.2 meV/kbar, which is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge1−xSnx alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge0.97Sn0.03 with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge1−xSnx layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed.

On the tin impurity in the thermoelectric compound ZnSb: Charge-carrier generation and compensation

The technique for measuring the Hall coefficient and electrical conductivity in the thermal cycling mode is used to study the effect of the Sn impurity on the microstructure and properties of pressed ZnSb samples. Tin was introduced as an excess component (0.1 and 0.2 at %) and as a substitutional impurity for Zn and Sb atoms in a concentration of (2–2.5) at % The temperature dependences of the parameters of lightly doped samples are fundamentally like similar curves for ZnSb with 0.1 at % of Cu. The highest Hall concentration, 1.4 × 1019 cm–3 at 300 K, is obtained upon the introduction of 0.1 at % of Sn; the dimensionless thermoelectric figure of merit attains its maximum value of 0.85 at 660 K. The experimental data are discussed under the assumption of two doping mechanisms, which are effective in different temperature ranges, with zinc vacancies playing the decisive role of acceptor centers. In two ZnSb samples with SnSb and ZnSn additives, the charge-carrier compensation effect is observed; this effect depends on temperature and markedly changes with doping type. As in p-type AIV–BVI materials with a low Sn content, hole compensation can be attributed to atomic recharging Sn2+ → Sn4+. Types of compensating complexes are considered.

Titration and quantification of open and closed Lewis acid sites in Sn-Beta zeolites that catalyze glucose isomerization

Methods to quantify framework Lewis acidic Sn4+ sites in zeolite Beta (Sn-Beta) with four Lewis base titrants (pyridine, deuterated acetonitrile, n-propylamine, ammonia) were developed using infrared (IR) spectroscopy or temperature programmed desorption (TPD). Integrated molar extinction coefficients (E, cmμmol−1) were measured for IR bands of pyridine adsorbed to Lewis acidic Sn sites (E(1450cm−1)=1.42±0.30) and of CD3CN adsorbed to open (E(2316cm−1)=1.04±0.22) and closed (E(2308cm−1)=2.04±0.43) Sn sites, and differ from analogous E values for Lewis acidic Al sites by up to 3.6×. TPD of Sn-Beta samples after saturation with NH3 or n-propylamine (NPA) and purging to remove physisorbed species also enabled quantification of Lewis acid sites, which is seldom performed despite analogous methods that use such titrants to quantify Brønsted sites in solid acids. These four Lewis bases titrated Lewis acidic Sn sites with equimolar stoichiometry and counted similar numbers of Sn sites on low-defect Sn-Beta samples synthesized in fluoride media (Sn-Beta-F) with high Sn content (Si/Sn <150). NPA binding on residual silanol defect sites, however, caused overestimation of Sn sites by TPD on Sn-Beta-F samples with low Sn content (Si/Sn >175) or high defect Sn-Beta samples prepared via post-synthetic insertion of Sn atoms into framework vacancy defects of dealuminated Beta zeolites (Sn-Beta-OH). Molar ratios of open-to-closed Sn sites varied widely (0.29–1.64) among the eight Sn-Beta samples studied here. Open Sn sites have been proposed as the dominant active sites for aqueous-phase glucose–fructose isomerization via intramolecular 1,2-hydride shift, consistent with successive poisoning of Sn-Beta samples with pyridine prior to measurement of initial glucose isomerization rates that suppressed reactivity at pyridine uptakes similar to the number of open Sn sites counted ex-situ by CD3CN. Measured first-order glucose isomerization rate constants in water (per open Sn, 373K), which reflect free energy differences between isomerization transition states and two coordinated water molecules at Sn sites, were ∼50× higher on hydrophobic Sn-Beta-F than on hydrophilic Sn-Beta-OH zeolites. The characterization methods reported herein enable normalization of initial glucose isomerization turnover rates on Sn-Beta zeolites by their number of open Sn sites, as required prior to interpreting the catalytic consequences of structural heterogeneities introduced by differences in sample preparation or treatment history.

Oxygen deficiency and Sn doping of amorphous Ga2O3

The potential of effectively n-type doping Ga2O3 considering its large band gap has made it an attractive target for integration into transistors and solar cells. As a result amorphous GaOx is now attracting interest as an electron transport layer in solar cells despite little information on its opto-electrical properties. Here we present the opto-electronic properties, including optical band gap, electron affinity, and charge carrier density, for amorphous GaOx thin films deposited by pulsed laser deposition. These properties are strongly dependent on the deposition temperature during the deposition process. The deposition temperature has no significant influence on the general structural properties but produces significant changes in the oxygen stoichiometry of the films. The density of the oxygen vacancies is found to be related to the optical band gap of the GaOx layer. It is proposed that the oxygen deficiency leads to defect band below the conduction band minimum that increases the electron affinity. These properties facilitate the use of amorphous GaOx as an electron transport layer in Cu(In,Ga)Se2 and in Cu2O solar cells. Further it is shown that at low deposition temperatures, extrinsic doping with Sn is effective at low Sn concentrations.

Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 − x)(Bi0.5Na0.5TiO3)–x(SrNb2O6)

Lead-free compositions (1 − x) (Bi0.5Na0.5TiO3)–x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN (x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie–Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole–Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

High hole mobility tin-doped polycrystalline germanium layers formed on insulating substrates by low-temperature solid-phase crystallization

We investigated the effects of incorporation of 0%–2% tin (Sn) into amorphous germanium (Ge) on its crystallization behavior and electrical properties. Incorporation of only 0.2% Sn caused the polycrystallization temperature of Ge to lower from 450 to 430 °C, while a polycrystalline Ge1−xSnx layer with high crystallinity compared to that of polycrystalline Ge was formed by incorporation of 2% Sn. A polycrystalline Ge1−xSnx layer with a low Sn content of 2% annealed at 450 °C exhibited a Hall hole mobility as high as 130 cm2/V s at room temperature even though it possessed a small grain size of 20–30 nm. The Hall hole mobility of a poly-Ge1−xSnx layer with an Sn content of 2% was four times higher than that of a polycrystalline Ge layer and comparable to that of single-crystalline silicon.

Measurement of Recombination Lifetimes in Gesn Alloys

Silicon photonics requires the development of Si-based lasers, modulators, waveguides, and detectors operating in the infrared beyond the band gap of silicon. A number of approaches to solving this problem have been pursued, including epitaxial growth of lower band gap materials on Si. The SiGe alloy system was explored for many years, but limitations in quality due the large lattice mismatch between Si and SiGe with high amounts of Ge, as well as the band gap (0.66 eV at its lowest for pure Ge) and its indirect nature, have prevented its widespread use. Integration of III-V materials such as InGaAs has also been tried extensively, but the problems of phase segregation and film quality have not been overcome. The GeSn alloy system has been gaining attention in the photonics world due to its unique optical properties, and the growth of these alloys on Si platforms has jumpstarted efforts to employ this technology for the fabrication of CMOS-compatible infrared optoelectronics. These crystalline alloy films are grown directly on Si or Ge-buffered Si, have band gaps below that of Si or Ge, and are grown to thicknesses of up to 1 µm. Additionally, the band gap of GeSn should be direct for concentrations greater than about 10% Sn. Much work has been done on the development of GeSn materials, and theoretical designs for lasers based on these alloys have been appearing in the literature frequently. However, the realization of complex optoelectronic devices like laser diodes requires materials with long recombination lifetimes to achieve population inversion. Thus, the study of recombination lifetimes in GeSn alloys is of paramount importance to the actualization of GeSn lasers. Unfortunately, the standard method of time-resolved photoluminescence (TRPL) is not well-suited to the study of GeSn alloys. For low Sn contents (<10% Sn), the band gap is indirect, so the intensity of optical emission is not high. Such a measurement would require single photon counting, but single photon detectors are not available at the emission wavelengths for the materials of interest. Conductivity-based methods should be more suitable, but the standard techniques of microwave photoconductive decay (µ-PCD) and RF-coupled photoconductive decay (RFPCD) suffer from low sensitivity in thin films or low temporal resolution. In this work, we employ a new conductivity-based method for measurement of recombination lifetimes in thin film GeSn alloys. The method of transmission-modulated photoconductive decay (TMPCD) uses the transverse transmission of microwaves through a thin film, allowing for a very large interaction volume between the free carriers and the microwaves, thereby increasing the sensitivity for thin film materials. We will discuss this new method and show preliminary results on GeSn films with up to 7% Sn.

Effect of Tin Oxide Additive on the Suppression of Dendrite Growth of Zinc Electrodeposits

Unlike the market acceptance of Zn-air primary battery, the Zn-air secondary battery is not yet commercialized, mainly due to its poor cycling stability. Although a number of issues have been raised as possible reasons for its low electrical rechargeability, the dendrite growth of Zn during charging process might be most critical because it leads to short circuits and thereby catastrophic failure. Many inorganic additives have been reported for the suppression of the dendritic growth of Zn electrodeposits. For example, it is known that a small amount of Pb ions in an alkaline solution effectively suppresses the Zn dendritic growth. Nevertheless, the environmental issues of Pb-containing additive drive the researchers to search for its alternatives. Sn is cost effective as well as environmentally friendly. Since it has higher reduction potential than Zn, it might be co-deposited with Zn to possibly change the growth habit of Zn dendrite. In fact, it has been reported that Sn ions affected the Zn deposition on a Zn single crystal at the very low Sn content, implying that Sn can be a possible option to toxic and expensive additives. In this work, we report that SnO additive significantly changes the morphology of Zn electrodeposits and suppresses quite well its dendritic growth. From the cyclic voltammograms at different SnO contents, it is proved that a few milli-moles of Sn ions in the electrolyte have a strong effect on the Sn deposition process. Moreover, the microscopic observation reveals that the non-uniform and dendritic growth of Zn electrodeposits is considerably suppressed at high content of SnO additive. From the depth profiling of the composition of Zn electrodeposit, it is confirmed that Sn is co-deposited with Zn during the course of deposition process, strongly indicating that the incorporated Sn interferes the dendritic growth of Zn. However, the addition of excess SnO resulted in a rough surface and crumbling porous particles containing large amount of Sn phase. In this presentation, an optimal SnO content required for the creation of dense Zn electrodeposits will be highlighted. Moreover, the possible mechanism of dendrite growth suppression by Sn ions will be further discussed.

Mid-infrared luminescence from Sn-modified PbSe quantum dots in silicate glasses

Infrared photoluminescence (PL) properties of Sn-modified PbSe quantum dots (QDs) in silicate glass were investigated. The QDs' sizes were controlled by changing the heat treatment temperatures. The longest absorption peak from Sn-modified PbSe QDs was centered at 2590nm, and the PL band extended to 2650nm. X-ray diffraction peaks indicated that the PbSe QDs formed in the glass matrix although low Sn content resulted in no obvious difference between PbSe QDs and Sn-modified PbSe QDs. Sn was found in QDs that proves the incorporation of Sn into PbSe QDs. The proposed composition of the Sn-modified PbSe QDs was Pb0.92Sn0.08Se with a band gap of ~0.13eV; the small amount of Sn changed the energy structure of QDs, narrowed the band-gap, and increased the PL emission wavelength.

Why Sn doping significantly enhances the dielectric properties of Ba(Ti 1-x Snx)O3.

Through appropriate doping, the properties of BaTiO3-based ferroelectrics can be significantly enhanced. To determine the physical process induced by the doping of Sn atoms in Ba(Ti0.8Sn0.2)O3, we performed high-resolution scanning transmission electron microscopy experiments and observed that the regions with low Sn content formed polar nano regions (PNRs) embedded in the matrix in Ba(Ti0.8Sn0.2)O3. The interactions among Sn, Ti, Ba and O atoms were determined using first principles calculations. Based on the characteristics of the electronic structure and crystal lattice strain fields, the effects of doping with Sn were investigated. The Sn doping not only changed the electronic structure of the crystal but also increased the dielectric properties of the PNRs. Moreover, the Sn doping was also responsible for the diffuse phase transition of the Ba(Ti1-xSnx)O3 material. The effects mentioned in this paper are universal in lead-free ferroelectrics, and similar elements such as Sb, Mg, and Zr may have the same functions in other systems. Thus, these results provide guidance for the design of the doping process and new systems of ferroelectric or relaxor materials.

The Agan epithermal gold-silver deposit and prospects for the discovery of high-sulfidation mineralization in northeast Russia

The Arman volcanotectonic depression (VTD) containing the Agan deposit is distinguished as the most promising area for the discovery of high-sulfidation (HS) epithermal Au deposit during prospecting in the Central Okhotsk ore district of the Okhotsk-Chukotka volcanogenic belt (OChVB). Studies reveal that the volcanic rocks of the Agan deposit strongly differ from those of the reference HS-type epithermal deposits. It was found that quartz-alunite metasomatites in the ore field are characterized by low Au content and Sn content two orders of magnitude higher than those of Cu and Mo. The pair-correlation coefficients are Kcor (Au-Sn) = 0.73 and Kcor(Au-Cu) = 0.22. The ore bodies of the Agan deposit do not contain enargite and luzonite—the main indicator minerals for Au productive HS-type mineralization; porous (“vuggy”) quartz is weakly manifested. In terms of the mineral complex, the epithermal mineralization revealed in the metasomatites of the deposit is close to the intermediate sulfidation type. At the same time, this mineralization, in many of its features, is similar to the mineralization developed in siliceous and quartz-alunite lithocaps, which are formed above degassing intrusions. In this setting, HS-type ore-bearing fluids either are not formed in the system or do not reach epithermal depths.

Influence of Sn content on the hydrogenation of crotonaldehyde catalysed by colloidally prepared PtSn nanoparticles.

Bimetallic PtSn nanoparticles (NPs) of well-defined size and metal composition were prepared by means of colloidal methods. The mean particle diameter was about 2 nm for all samples irrespective of the Pt/Sn-ratio, which enables a systematic study of the influence of the composition on the catalytic properties while excluding particle size effects. The hydrogenation of crotonaldehyde was investigated as a reaction for which chemoselectivity is known to be a challenging task. Already very low atomic Sn contents (≈10%) were found to lead to a significantly improved activity which may be attributed to an electronic effect of Sn on Pt. For further increasing tin contents the activity decreased gradually. This trend was accompanied by a steady increase in selectivity towards the desired product (crotylalcohol). The results show that the highest crotylalcohol time yields can be obtained by using catalysts with an atomic Sn content of approximately 23%. In contrast, maximum crotylalcohol selectivities are achieved by using catalysts with a high tin content (>50%).

Creep performance of Zr-1Nb-0.75Sn-0.1Fe cladding tubes with optimized Sn content

Creep properties of stress-relieved Zr-1Nb-0.75Sn-0.1Fe alloy with a lower Sn content were studied. Zr-1Nb-0.75Sn-0.1Fe alloy was found to have stress exponents of 6–7, independent of stress level, unlike Zr-1Nb-1Sn-0.1Fe alloy, in which the transition of stress exponent with increase of stress was observed. The constancy of stress exponent, without the transition observed in Zr-1Nb-0.75Sn-0.1Fe alloy with lower Sn content, is associated with the decrease of Sn atoms. The activation energies for creep deformation were calculated to be between 210 and 260 kJ/mol for the Zr-1Nb-0.75Sn-0.1Fe alloy with a lower Sn content. The slightly smaller creep activation energy in Zr-1Nb-0.75Sn-0.1Fe, compared with that of Zr-1Nb-1Sn-0.1Fe alloy, is thought to be attributed to the lower Sn content. The creep data obtained at different temperatures and stress fell close to a single line, suggesting the creep life of Zr-1Nb-0.75Sn-0.1Fe alloy with a lower Sn content is well expressed by the Larson-Miller Parameter.

Observation of heavy- and light-hole split direct bandgap photoluminescence from tensile-strained GeSn (0.03% Sn)

Temperature- (T-) and laser power-dependent photoluminescence (PL) measurements have been made for the tensile-strained, undoped GeSn (0.03% Sn) film grown on Si substrate. The PL results show not only clear strain-split direct bandgap transitions to the light-hole (LH) and heavy-hole (HH) bands at energies of 0.827 and 0.851 eV at 10 K, respectively, but also clearly show both strong direct and indirect bandgap related PL emissions at almost all temperatures, which are rarely observed. This split of PL emissions can be directly observed only at low T and moderate laser power, and the two PL peaks merge into one broad PL peak at room temperature, which is mainly due to the HH PL emission rather than LH transition. The evolution of T-dependent PL results also clearly show the competitive nature between the direct and indirect bandgap related PL transitions as T changes. The PL analysis also indicates that the energy gap reduction in Γ valley could be larger, whereas the bandgap reduction in L valley could be smaller than the theory predicted. As a result, the separation energy between Γ and L valleys (∼86 meV at 300 K) is smaller than theory predicted (125 meV) for this Ge-like sample, which is mainly due to the tensile strain. This finding strongly suggests that the indirect-to-direct bandgap transition of Ge1−ySny could be achieved at much lower Sn concentration than originally anticipated if one utilizes the tensile strain properly. Thus, Ge1−ySny alloys could be attractive materials for the fabrication of direct bandgap Si-based light emitting devices.

Structural and Optical Properties of Ge1-XSnx Alloys Grown on GaAs (001) by R. F. Magnetron Sputtering

Ge1-xSnx alloys were grown on GaAs (001) substrates in a conventional R. F. magnetron sputtering system with two independent plasmas not simultaneous focus to substrate. We determined the in-plane and in-growth lattice parameters for different Sn concentrations by high resolution X-ray diffraction (HRXRD). We observed that Ge1-xSnx layers with low Sn concentrations have pseudomorphic characteristics. But this layers relax at Sn concentrations higher than the ones growth on Ge (001) substrates. Raman spectroscopy confirms the Sn concentrations of the Ge1-xSnx layers. We also determined the band gap transitions and we found that the indirect-direct band gap crossover occurs as is predicted in Ge1-xSnx alloys growth on Ge (001).