Increasing Sb Content Research Articles

Sb Doping of Metallic CuCr2S4 as a Route to Highly Improved Thermoelectric Properties

We report for the first time the thermoelectric properties of CuCr2–xSbxS4 (0.22 ≤ x ≤ 0.5). Although CuCr2S4 has been reported to be a metallic compound, addition of Sb shifts the material toward the semiconductor side. This is confirmed by band structure calculations of CuCr2–xSbxS4 (x = 0, 0.25, 0.5) models. Increasing Sb content enhances the power factor. However, beyond x = 0.3, further Sb addition lowers the electrical conductivity and power factor. A very interesting point is the simultaneous increase of the Seebeck coefficient as well as the electrical conductivity with increasing temperature, which acts like a variable range hopping (VRH) compounds but possesses much better properties than those having VRH. Samples were annealed for 48 h prior to thermoelectric properties measurements to have a reliable dimensionless figure of merit (ZT). An attractive ZT of 0.43 is obtained at ∼650 °C. The attractive thermoelectric properties we discovered by driving a metal compound into a semiconductor make th...

Experimental and theoretical investigation of the chromium–vanadium–antimony system

Abstract The binary compound V3Sb (V2.64Sb, V3Sb and V3.24Sb) was synthesized as thin multilayered films with varying V:Sb ratios. The V-content determines the crystallization temperature and it is highest for the film with the lowest amount of V. Ternary chromium–vanadium–antimony (Cr–V–Sb) films were prepared containing Cr from 10 to 51 at-% with the Sb content fixed to yield M3Sb (M=Cr, V). In the as-deposited state the layers are already interdiffused which is most likely caused by the very low repeating unit thickness between 0.29 and 0.68 nm investigated by X-ray diffraction experiments. All ternary compounds crystallized from the amorphous state with crystallization temperatures depending more on the repeating unit thickness than on chemical composition. For most samples the simultaneous crystallization of the two phases M3Sb (A15 structure type) and MSb is observed. The crystalline A15 compounds are only stable in a limited temperature range and decompose at elevated temperatures. Compared to the binary Cr–Sb system crystallization of the hexagonal phase MSb (M=Cr, V) occurs at remarkably higher temperatures, i.e. in the ternary system nucleation and crystallization of this phase is hindered. The chemical composition requires short-range composition fluctuations to nucleate the binary phase. The first principles total energy calculations using the spin-polarized relativistic Korringa–Kohn–Rostoker (SPR-KKR) method confirm the experimental observations concerning the concentration-dependent stability of different phases of the Cr–V–Sb system. For the ratio M:Sb=3:1 the system is preferably stabilized in the A15 crystal structure for all possible Cr and V concentrations, while an increase of Sb content up to M:Sb=2:1 results in the stabilization of the Ni2In structure for almost all Cr concentrations. Only in the V-rich regime of the system the Heusler Ni2MnAl-type structure was found to be energetically more preferable.

Physical and optical properties of bulk and thin films of a–Ge–Sb–Te lone-pair semiconductors

ABSTRACTPhysical parameters and their correlation with optical band gap and refractive index for amorphous Ge20Te80-xSbx (x = 0, 2, 4, 6, 8, 10) lone-pair semiconductors were discussed. Using average coordination number lone-pair electrons (L) were calculated and found to decrease with an increase in the Sb content. However, L value greater than 3 indicated that Ge20Te80-xSbx alloys can retain their vitreous nature. The density of alloys was measured both experimentally and theoretically. Increased density values with the increase of Sb content further accounts for the concurrent increase in the refractive index values. The results were explained on the basis of increased polarizability and larger Bohr radius of Sb. Compactness of the structure was found to decrease with the alterations of the atomic arrangements. Molar volume (calculated from the measured density values) found to decrease with Sb content. The number of atoms per unit volume (N) was calculated, using molar volume and average coordination number and were found to increase. This increase in N accounts for the decrease in the optical band gap. Other optical parameters viz. optical density, penetration depth and Urbach energy were also calculated. An increase in Urbach energy showed the reduction in band tail width with increased defect concentration. Positions of the conduction bands and valence bands were found to shift towards the Fermi edge, which accounts for the reduction in the optical band gap. Chemical bond approach (CBA) model was applied to estimate the cohesive energy of the system and found to decrease with the Sb content. A linear relation is found between the behaviour of cohesive energy and band gap (calculated both experimentally and theoretically). Deviation of stoichiometry confirmed chalcogen-rich region for all the compositions. The mean bond energy was found to be proportional to the glass transition temperature and showed maxima at the chemical threshold. The obtained results were discussed in terms of average coordination number or equivalently structure of the glassy matrix, decrease in average stabilization energy, electronegativity and average heat of atomization of the system. In amorphous materials, maximum optical non-linearity has been predicted. To open the prospects of Ge–Te–Sb vitreous system for non-linearity, Sheikh and Bahae relationship was applied, using experimentally obtained parameters, at a telecommunication wavelength. Obtained results showed a decent agreement with values available in the literature at 0.8 eV or 1550 nm. Non-linear refractive indices, almost three orders higher than silica glass, were obtained. These results may lead to yielding more sensitive optical limiting devices, and these glasses may be used as an optical material for a high-speed communication fibre.

Influence of Sb addition on the structural and optical characteristics of thermally vacuum evaporated SbxSe1−x thin films

Binary chalcogenide glasses of SbxSe1−x (0.1, 0.2 and 0.3) were synthesized by the conventional melt quenching technique. Thin films of these glasses were deposited by vacuum evaporation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that, the deposited films have amorphous nature. The optical properties were studied in the wavelength range 200–2500 nm by using Swanepoel method, which is based on the presence of interference fringes. Type of transition in the films is found to be indirect allowed with a value of energy gap decrease with increasing Sb-content due to the increasing of concentration of the localized states. Optical absorption parameters such as Urbach energy, skin depth, steepness, electron-phonon interaction were determined and showed composition dependence. The obtained indirect optical energy gap was found to decrease with increasing Sb-content due to the increasing of concentration of the localized states. In addition, the results indicate that the values of refractive index gradually increase with increasing Sb content which is related. The dispersion characteristics were discussed in terms of the single oscillator expressed by Wemple– Di-Domenico (WD). The obtained dispersion parameters were extracted and showed compositional dependence.

Mechanical and thermoelectric properties of Bi2−xSbxTe3 prepared by using encapsulated melting and hot pressing

Bi2-xSbxTe3 (x = 1.4 - 1.7) solid solutions were synthesized by using encapsulated melting (EM) and were consolidated by using hot pressing (HP). The lattice constants decreased with increasing Sb content, which indicated that solid solutions were successfully synthesized. The relative densities of all the hot-pressed specimens were higher than 97.9 %. X-ray diffraction patterns, pole figures and electron backscattered diffraction spectra of all the hot-pressed specimens indicated randomly oriented textures. Very low values of the orientation factor (F) were obtained, Fmin = 0.008 for Bi0.4Sb1.6Te3 hot-pressed at 673 K and Fmax = 0.115 for Bi0.4Sb1.6Te3 hot-pressed at 723 K, which implied that the microstructures were highly isotropic. A bending strength of 46 MPa and a Vickers hardness of 94 Hv were attained for Bi0.4Sb1.6Te3 hot-pressed at 648 K. However, the mechanical properties were degraded with increasing HP temperature owing to grain growth. An increased HP temperature did not affect the electrical properties significanctly. The carrier concentration increased with increasing Sb content, and the specimen with x = 1.4 showed nondegenerate semiconductor behavior whereas those with x ≥ 1.5 behaved as degenerate semiconductors. All specimens showed p-type conduction, which was confirmed from the positive signs of the Seebeck coefficient and the Hall coefficient. The increased Sb content caused a shift in the peak values of the Seebeck coefficient to higher temperatures and an enhancement of the power factor. The electronic thermal conductivity decreased, but the lattice thermal conductivity increased, with increasing Sb content. The lowest theraml conductivity of 0.83 Wm -1K -1 was obtained at 373 K for Bi0.4Sb1.6Te3. The maximum dimensionless figure of merit, ZTmax = 1.1, was achieved at 323 K for Bi0.4Sb1.6Te3.

Thermoelectric properties of dense Sb-doped SnO2 ceramics

In the present study thermoelectric properties of spark plasma sintered and subsequently air-annealed Sn1-xSbxO2 (x = 0, 0.01, 0.03, 0.05) ceramic samples were characterized. It was observed that addition of Sb greatly affects density, microstructure and thermoelectric properties of SnO2. Grain size decreases and the microstructure becomes more homogeneous with increasing Sb content in the Sn1-xSbxO2 samples from x = 0.01 to 0.05. The thermal conductivity and Seebeck coefficient of the Sb doped samples decreases with an increase in Sb concentration, while electrical conductivity increases up to a maximum at Sb doping level of x = 0.03 and then decreases at x = 0.05. The highest thermoelectric figure of merit of ZT ≈ 0.06 at 1073 K was exhibited by the sample of composition Sn0.99Sb0.01O2.

Subcellular distribution and chemical forms of antimony in Ficus tikoua

ABSTRACTFicus tikoua (F. tikoua) was a potential species for antimony (Sb) phytoremediation due to its wide growth in the mining area. However, little was known about its tolerance mechanisms toward Sb. The determination of the distribution and chemical speciation of Sb in F. tikoua is essential for understanding the mechanisms involved in Sb accumulation, transportation, and detoxification. The present study investigated the subcellular distribution and chemical forms of Sb in F. tikoua. The plant was exposed to different Sb concentrations (0, 30, 90, and 180 μmol/L) for 30 days. The results showed that F. tikoua possessed a marked ability to tolerate and accumulate Sb. The proportional Sb increased with increasing Sb concentration in the solution, and the highest Sb concentration occurred in roots (1274.5–1580.9 mg/kg), followed by stems (133.5–498.9 mg/kg) and leaves (4.1–15.7 mg/kg). In the subcellular sequestration of Sb in F. tikoua, the largest accumulation of Sb occurred in cell walls (72.4–87.5%) followed by cytoplasmic organelles (8.2–18.6%) and cytoplasmic supernatant. The results suggested that cell walls act as important protective barriers against Sb toxicity in F. tikoua. Although Sb in all plant tissues found primarily in the fractions extracted by ethanol and distilled water, the current study found that the Sb amounts in the HAc-extractable fraction, HCl-extractable fraction, and residue fraction increased at the highest Sb level (180 μmol/L) compared to that under lower Sb levels. These results indicate that excessive Sb accumulated in F. tikoua under Sb stress is bound to non-dissolved or low-bioavailable compounds, a biochemical mechanism that benefits F. tikoua because it helps alleviate Sb toxicity.

Influence of Sb addition on the structural and optical characteristics of thermally vacuum evaporated Se85SbxS15-x thin films

Films of Se85SbxS15−x (x=1, 3, 7 and 9at.%) were prepared by conventional thermal evaporation under vacuum of 10−3Pa. The structural characteristics confirm that the prepared films are amorphous in nature. Optical properties were estimated using spectrophotometric measurements of transmittance and reflectance in a wide wavelength range (200–2500nm). The optical constants were extracted from the interference maxima and minima using the Swanepole method. The refractive index dispersion was analyzed on the basis of the single oscillator model, expressed by Wemple–Didomenico. The oscillator energy, the dispersion energy, the high frequency dielectric constant and the lattice dielectric constant are found to be Sb content dependent. The type of electronic transition of the films was found to be indirect allowed transition with energy gaps varies with the addition of Sb content. The energy gap was found to increase while urbach energy decreases with increasing Sb content.

Magnetic and magnetocaloric properties of ferromagnetic shape memory alloy Mn50Ni40In10−xSbx

Abstract Magnetic properties of Mn50Ni40In10−xSbx alloys and thermal history effect on the magnetization behavior and magnetic entropy change of Mn50Ni40In9Sb1 have been systematically studied. It indicates that the martensitic transformation temperature gradually increases with the increase of Sb content. Meanwhile, the overall magnetization of austenite decreases and that of martensite increases. The magnetization behavior, the critical magnetic field for martensite-to-austenite transformation and the magnetic entropy are very sensitive to the thermal history effect. The maximum magnetic entropy change is up to 27.1 J kg−1 K−1 in Mn50Ni40In9Sb1 alloy under a magnetic field of 30 kOe with continuous heating method.

The low and high temperature thermoelectric properties of Sb doped Cu2SnSe3

The effect of Sb doping on the thermoelectric properties of Cu2SnSe3 was investigated. The Cu2Sn1⿿xSbxSe3 (0⿤x⿤0.04) compounds were prepared by solid state synthesis. The powder X-ray diffraction pattern of the samples showed a cubic structure (space group F4¯3m). The electrical resistivity decreased with increase in Sb content up to x=0.02, then it increased with further increase in x. The electrical resistivity data follows variable hopping model at low temperatures. The Seebeck coefficient for all the samples is positive and analysis of data confirms that the variable hopping process is operative at low temperatures. The thermal conductivity is found to decrease with increase in Sb concentration, presumably due to point-defect scattering as a result of Sb substitution. The highest value of figure of merit at 400K is equal to 0.0137 for the sample Cu2Sn0.99Sb0.01Se3 which is about eight times greater than that of the pristine sample.

Thermally Activated Processes of the Phase Composition and Structure Formation of the Nanoscaled Co–Sb Films

It is investigated the formation of the phase composition and structure in the nanoscaled CoSbx (30 nm) films deposited by the method of molecular-beam epitaxy on the substrates of the oxidated monocrystalline silicon at 200 C and following thermal treatment in vacuum in temperature range of 300-700 C. It is established that the films after the deposition are polycrystalline without texture. With increase in Sb content the formation of the phase composition in the films takes place in such sequence as this is provided by phase diagram for the bulky state of the Co-Sb system. At annealing in vacuum at temperature above 450-500 C a sublimation not only of the crystalline Sb phase but from the antimonides occurs.

Phase Segregation and Superior Thermoelectric Properties of Mg2Si(1-x)Sb(x) (0 ≤ x ≤ 0.025) Prepared by Ultrafast Self-Propagating High-Temperature Synthesis.

A series of Sb-doped Mg2Si(1-x)Sb(x) compounds with the Sb content x within 0 ≤ x ≤ 0.025 were prepared by self-propagating high-temperature synthesis (SHS) combined with plasma activated sintering (PAS) method in less than 20 min. Thermodynamic parameters of the SHS process, such as adiabatic temperature, ignition temperature, combustion temperature, and propagation speed of the combustion wave, were determined for the first time. Nanoprecipitates were observed for the samples doped with Sb. Thermoelectric properties were characterized in the temperature range of 300-875 K. With the increasing content of Sb, the electrical conductivity σ rises markedly while the Seebeck coefficient α decreases, which is attributed to the increase in carrier concentration. The carrier mobility μ(H) decreases slightly with the increasing carrier concentration but remains larger than the Sb-doped samples prepared by other methods, which is ascribed to the self-purification process associated with the SHS synthesis. In spite of the increasing electrical conductivity with the increasing Sb content x, the overall thermal conductivity κ decreases on account of a significantly falled lattice thermal conductivity κ(L) due to the strong point defect scattering on Sb impurities and possibly enhanced interface scattering on nanoprecipitates. As a result, the sample with x = 0.02 achieves the thermoelectric figure of merit ZT ∼ 0.65 at 873 K, one of the highest values for the Sb-doped binary Mg2Si compounds investigated so far. A subsequent annealing treatment on the sample with x = 0.02 at 773 K for 7 days has resulted in no noticeble changes in the thermoelectric transport properties, indicating an excellent thermal stability of the compounds prepared by the SHS method. Therefore, SHS method can serve as an effective alternative fabrication route to synthesize Mg-Si based themoelectrics and some other functional materials due to the resulting high performance, perfect thermal stability, and feasible production in large scale for commercial application.

Thermal stability of Sb–V2O5–TeO2 semiconducting oxide glasses using thermal analysis

Thermal analysis of the ternary xSb−(60−x) V2O5–40TeO2 oxide glasses (with 0⩽x⩽15 in mole%) has been carried out employing the differential scanning calorimetry (DSC) at heating rates φ=3, 6, 9 and 12K/min. The compositional and heating rate dependence of the glass transition temperature (Tg) is discussed. Using the DSC outputs, the compositional dependence of the activation energy (ΔH∗) of glass transition (the heat absorbed in the endothermic region respecting to Tg) is investigated. The dependence of Tg on φ was used to study the applicability of different empirical formulas describing the glass transition. For these glasses, Moynihan and Kissinger formulas were applied and different values of ΔH∗ were obtained at different heating-rate regions. Also, the fragility parameter (m=ΔH∗/RTg) was obtained and discussed upon the data of thermal stability parameter (S), glass forming tendency (Kgl), CV=[V4+]/Vtot as the ratio of the content of reduced vanadium ions and also oxygen molar volume (VO∗). Results show that glasses with x⩾10 (especially for x=12) have relatively high thermal stability, high glass forming tendency and so lower non-bridging oxygen atoms (NBOs), which introduce them as good candidates for devices with higher resistance against thermal shocks, such as optoelectronic devices. Also, the Seebeck coefficient (Q) of these glasses was measured at different temperatures; for the under studied samples, the thermoelectric power at different temperatures was within the range of ((−392)−(−691))μVK−1, showing the increasing trend with increase of Sb content. The negative sign of Q indicates that these glasses are n-type semiconductors; results show the compositional dependence of Q, indicating that S increases with increasing of Sb content and CV; thus, the important parameter determining Q is the composition and therefore CV.

Structural and optical analyses of polycrystalline Zn1−xSbxSe thin films prepared by resistive heating technique

Here we report the influence of Sb doping on the structural and optical properties of Zn1−xSbxSe (0⩽x⩾0.15) thin films prepared by thermal evaporation technique on glass substrate. Various characterization techniques such as X-ray diffraction (XRD), EDS, Raman spectroscopy and spectroscopic ellipsometer are employed to assess the structural and optical properties of the deposited films. XRD analysis reveals the formation of polycrystalline cubic structure having preferred growth orientation along (111) plane without any evidence of secondary phases. Crystallographic parameters like grain size, micro strain, dislocation density, number of crystallites per unit area and texture coefficient point out the structural modification in ZnSe films with Sb inclusion. Raman analysis shows the existence of three 1LO, 2LO and 3LO phonon modes at 251, 511 and 745cm−1 in pure ZnSe while 3LO mode disappears by the incorporation of Sb atoms in ZnSe matrix. Increase in FWHM of Raman peaks with Sb concentration also indicates the change in crystalline quality of ZnSe films which is in accordance with our XRD results. Spectroscopic ellipsometry results demonstrate a decreasing trend for the optical band gap energy (from 2.61eV to 1.81eV) with increasing Sb content.

Effect of Sb addition on linear and non-linear optical properties of amorphous Ge–Se–Sn thin films

Optical characterization of amorphous thin films of Ge20Sn10Se70−xSbx (x=0, 3, 6, 9, 12, 15) has been carried out. Thin films were deposited onto pre cleaned glass substrates using thermal evaporation technique. Transmission spectra of the films were recorded, for normal incidence, in range 400–2400nm. Refractive index of the films was calculated using the envelope method by Swanepoel. Dispersion analysis has been carried out using single effective oscillator model. Other optical constants such as absorption coefficients, extinction coefficients have also been evaluated. Tauc plots were used to evaluate the optical band gap. The refractive index has been found to be increasing while the band gap decreases with increasing Sb concentration. The observed optical behavior of the films has been explained using chemical bond approach. Cohesive energy is found to be decreasing in the present work, which reflects that bond strength decreases with the increasing content of Sb. Non-linear optical parameters (i.e. n2 and χ(3)) have been derived from linear optical parameters (i.e. n, k, Eg). Observed changes in linear and non-linear parameters have been reported in this study.

Thermoelectric Power Measurements of xSb-(60-x)V2O5-40TeO2 Glasses

Bulk xSb-(60-x)V2O5-40TeO2 glass systems (with 0 ≤ x ≤ 15 in mol.%) were prepared by using the standard melt quenching procedure, and their Seebeck coefficients, S, were measured within the temperature range of 250–470 K. For the understudied samples, the thermoelectric powers at typical temperatures of 296 K, 370 K and 407 K were measured, and were in the ranges (−405) to (−698) μVK−1, (−394) to (−685) μVK−1 and (−392) to (−691) μVK−1, respectively. The selection of typical temperatures aims at the evaluation of the trend of figure of merit in these glasses. Based on the negative sign of S, the present glasses were found to be n-type semiconductors; also, the experimental relationship between S and CV (CV = [V4+]/Vtot is the ratio of the content of reduced vanadium ions) satisfied the theoretical Heikes formula, relating S to ln(CV/1 − CV), and also the Mackenzie formula, relating S to ln([V5+]/[V4+]). The parameter \( \alpha^{\prime} \) in Heikes formula was determined to be ≪1 and so the small polaron hopping conduction mechanism was certified to occur in these glasses; this result confirms the previously reported results of direct current (DC) electrical conduction experiments on the same samples. Results of thermoelectric measurements show the compositional dependence of S on Sb content and CV, indicating that S increases with the increase in Sb content; these results show that the dominant factor determining S is CV. Also, figure of merit was determined for these glasses, which show the highest value for 60V2O5-40TeO2 glass system, as a good candidate in thermoelectric applications.

Material and device characteristics of InAs/GaAsSb sub-monolayer quantum dot solar cells

We have studied the material and photovoltaic characteristics of InAs/GaAsSb sub-monolayer quantum dot solar cells (QDSCs) with different Sb contents of 0%, 5%, 15%, and 20%. All QDSCs exhibit an extended external quantum efficiency (EQE) response in the wavelength range of 960–1000 nm that corresponds to sub-bandgap photon absorption. As Sb content increases from 5% to 20%, the cutoff wavelength in the EQE extends towards longer wavelength whilst the EQE in the wavelength region of 300–880 nm is lowered due to increased defect density. Compared to the QDSC (Sb 0%), an Sb incorporation of 5% enhances the short-circuit current density from 20.65 to 22.15 mA/cm2 induced by Sb surfactant effect. Since the open-circuit voltage and fill factor of the QDSC (Sb 5%) are comparable to those of the QDSC (Sb 0%), an enhancement in solar cell efficiency (10.5%) of the QDSC (Sb 5%) is observed. Further increasing Sb content to 15% and 20% results in the degradation of solar cell performance due to increased nonradiative recombination and large valence band offset in a type-II band line-up.

Growth and Characterization of InAs1–xSbx with Different Sb Compositions on GaAs Substrates**Supported by the Aeronautical Science Foundation of China under Grant No 20132435, the National High-Technology Research and Development Program of China under Grant No 2013AA031903, the National Natural Science Foundation of China under Grant Nos 61106013 and 61275107, and the China Postdoctoral Science Foundation under Grant No 2014M560936.

InAs1–xSbx with different compositions is grown by molecular beam epitaxy on (100)-oriented semi-insulating GaAs substrates. The increase of Sb content in the epilayer results in the deterioration of crystal quality and surface morphology. Hall measurements show that the carrier concentration increases with the composition of Sb. The electron mobility decreases initially, when Sb composition exceeds a certain value, and the mobility increases slightly. In this work, we emphasize the comparison of crystal quality, surface morphology and electrical properties of epilayers with different Sb compositions.

Bandgap tuning of GaAs/GaAsSb core-shell nanowires grown by molecular beam epitaxy

Semiconductor nanowires have been identified as a viable technology for next-generation infrared (IR) photodetectors with improved detectivity and detection across a range of energies as well as for novel single-photon detection in quantum networking. The GaAsSb materials system is especially promising in the 1.3–1.55 μm spectral range. In this work we present band-gap tuning up to 1.3 μm in GaAs/GaAsSb core–shell nanowires, by varying the Sb content using Ga-assisted molecular beam epitaxy. An increase in Sb content leads to strain accumulation in shell manifesting in rough surface morphology, multifaceted growths, curved nanowires, and deterioration in the microstructural and optical quality of the nanowires. The presence of multiple PL peaks for Sb compositions ≥12 at.% and degradation in the nanowire quality as attested by broadening of Raman and x-ray diffraction peaks reveal compositional instability in the nanowires. Transmission electron microscope (TEM) images show the presence of stacking faults and twins. Based on photoluminescence (PL) peak energies and their excitation power dependence behavior, an energy-band diagram for GaAs/GaAsSb core–shell nanowires is proposed. Optical transitions are dominated by type II transitions at lower Sb compositions and a combination of type I and type II transitions for compositions ≥12 at.%. Type I optical transitions as low as 0.93 eV (1.3 μm) from the GaAsSb for Sb composition of 26 at.% have been observed. The PL spectrum of a single nanowire is replicated in the ensemble nanowires, demonstrating good compositional homogeneity of the latter. A double-shell configuration for passivation of deleterious surface states leads to significant enhancement in the PL intensity resulting in the observation of room temperature emission, which provides significant potential for further improvement with important implications for nanostructured optoelectronic devices operating in the near-infrared regime.

Investigation of single-layer/multilayer self-assembled InAs quantum dots on GaAs1-xSbx/GaAs composite substrates

The structure-performance properties of single-layered and multi-layered InAs/GaAs1−xSbx quantum dot (QD) system, grown by molecular beam epitaxy on GaAs (001) substrates, have been investigated as a function of Sb concentration. Electron microscopy observations showed no significant crystalline defects for the single-layered InAs QDs (Sb 20%). X-ray diffraction analysis revealed that the increase of Sb concentration from 7.3% to 10.2% for the multi-layered QDs increased the strain relaxation from 0% to ∼23% and the dislocation density of GaAsSb layers went up to 3.6 × 109 cm−2. The peak energy of QD luminescence was red-shifted with increasing Sb concentration due to reduced strain inside QDs. Moreover, the carrier lifetime of the QDs was highly improved from 1.7 to 36.7 ns due to weak hole confinement as the Sb concentration was increased from 7.3% to 10.2%. These structures should be highly promising as the basis for photovoltaic solar-cell applications. Finally, the increased Sb concentration increased the thermal activation energy of electrons confined in the QDs from 163.7 to 206.8 meV, which was indicative of the improved thermal stability with Sb concentration.