Ga Sb Research Articles

Thin Ga(Sb,P)/GaP quantum wells with indirect band gap: Crystal structure, energy spectrum, exciton recombination and spin dynamics

Heterostructures with thin GaSb layers embedded in a GaP matrix are studied by transmission electron microscopy as well as steady-state and transient photoluminescence. For a single, one monolayer thick deposition with subsequent overgrowth, nonmonotonic Sb segregation results in self-organized Ga(Sb,P) double-quantum well (QW) formation. One QW is positioned deep in GaP at the designated place according to the heterostructure design, and the other QW is in the near surface region after 40 monolayers of GaP overgrowth. Both QWs are characterized by an indirect band gap. The band alignment in the QWs is identified as type I. In spite of the long (up to milliseconds) exciton lifetimes in the QWs in combination with the electron g factor of +2, the emission of the QWs demonstrates a low circular polarization degree in longitudinal magnetic fields as strong as 10 T. We demonstrate that the electron spin polarization in the Ga(Sb,P)/GaP heterostructure subject to a magnetic field occurs in the GaP layer, and spin-polarized charge carriers captured in the QWs store their spin orientation up to the millisecond time range, indicating very long spin relaxation times for the strongly localized electrons in the Ga(Sb,P)/GaP QWs.

Crystallization in Ga–Sb–Se glasses and influence of the Se content

Crystallization in glasses composed of Ga, Sb and Se has been studied as a function of Se content. Six glass compositions are selected (Ga8Sb27Se65, Ga12Sb23Se65, Ga8Sb32Se60, Ga10Sb30Se60, Ga8Sb37Se55 and Ga8Sb40Se52), with different Se contents. Glass-ceramics are obtained by heating the glass 5 °C above its glass transition temperature. Glasses and glass-ceramics are characterized by differential scanning calorimetry, Raman spectroscopy, infrared spectroscopy and X-ray diffraction. A correlation between the Se content, the nature of the phase crystallizing and the electrical conducting properties of the material is evidenced. On one hand, antimony selenide Sb2Se3 crystallizes in over-stoichiometric and stoichiometric glasses compared to the x Ga2Se3 -(100-x) Sb2Se3 line. On the other hand, an unknown phase crystallizes in sub-stoichiometric glasses, followed by Sb2Se3. The resulting glass-ceramics are characterized by a conductivity reaching up to 2 S·cm−1, two order of magnitude higher than other Se-based glass-ceramics.

Synthesis, structural, morphology, spectroscopic and optical study of new metal orthophosphate MII(Ga0.5Sb0.5)(PO4)2 (MII= Sr, Pb, Ba) compounds

This paper reports the synthesis, structure, BFDH crystal morphology, Raman and Infrared spectroscopic studies of three novel metal orthophosphate salts MII(Ga0.5Sb0.5)(PO4)2 (MII= Sr, Pb, Ba), abbreviated [Sr], [Pb], [Ba]. The structures of these phases are refined from X-ray powder diffraction data by the Rietveld method. The yavapaiite [Ba] phase is monoclinic of C2/m space group [Z=2; a= 8.106(4) Å; b= 5.178(3) Å c= 7.806(1) Å, β=94.79(4)°, V= 327(1) Å3]. Its structure consists of layers, running along the (a, b) plane, and built up of corner-connected Ga(Sb)O6 octahedra and PO43− tetrahedra. The two isotypic phases [Sr]/[Pb] of distorted yavapaiite structure crystallize in the monoclinic C2/c space group (Z=4) with parameters: a=16.455(4)/16.622(7) Å; b=5.158(1)/5.163(2) Å c= 8.005(1)/8.067(3) Å; β=115.49(1)/114.85(2)°, V= 613(1)/628(5) Å3. Their structures consist of MO10 (M= Sr, Pb), PO43− tetrahedra and Sb(Ga)O6 octahedra. In [Pb] phase, the Pb is surrounded by eight oxygen atoms (Pb-O: 2.65-2.77 Å) and two oxygen atoms forming abnormal bond distances Pb-O(4) [3.447(3)Å]. The BFDH crystal morphology predicts hight (h k l) facets for each compound, the center-to-plane distances dhkl are slightly strong in the distorted Yavapaiite [Pb/Sr] rather than in [Ba]. The IR and Raman study is performed based on theoretical group analysis considering Cs site symmetry of PO43− groups in [Ba], and Ci symmetry in [Pb]/[Sr] phases. The assignment and discussion of the observed bands were done by comparison with other yavapaiite materials. The UV–visible investigation reveals direct optical gap energies of values 4.16 eV for [Ba] and 4.24 eV for [Sr], indicating a semi-conducting nature of the prepared materials.

Electrical and structural properties of binary Ga–Sb phase change memory alloys

Material properties of Ga–Sb binary alloy thin films deposited under ultra-high vacuum conditions were studied for analog phase change memory (PCM) applications. Crystallization of this alloy was shown to occur in the temperature range of 180–264 °C, with activation energy >2.5 eV depending on the composition. X-ray diffraction (XRD) studies showed phase separation upon crystallization into two phases, Ga-doped A7 antimony and cubic zinc-blende GaSb. Synchrotron in situ XRD analysis revealed that crystallization into the A7 phase is accompanied by Ga out-diffusion from the grains. X-ray absorption fine structure studies of the local structure of these alloys demonstrated a bond length decrease with a stable coordination number of 4 upon amorphous-to-crystalline phase transformation. Mushroom cell structures built with Ga–Sb alloys on ø110 nm TiN heater show a phase change material resistance switching behavior with resistance ratio >100 under electrical pulse measurements. TEM and Energy Dispersive Spectroscopy (EDS) studies of the Ga–Sb cells after ∼100 switching cycles revealed that partial SET or intermediate resistance states are attained by the variation of the grain size of the material as well as the Ga content in the A7 phase. A mechanism for a reversible composition control is proposed for analog cell performance. These results indicate that Te-free Ga–Sb binary alloys are potential candidates for analog PCM applications.

Tailoring of Multisource Deposition Conditions towards Required Chemical Composition of Thin Films.

The model to tailor the required chemical composition of thin films fabricated via multisource deposition, exploiting basic physicochemical constants of source materials, is developed. The model is experimentally verified for the two-source depositions of chalcogenide thin films from Ga–Sb–Te system (tie-lines GaSb–GaTe and GaSb–Te). The thin films are deposited by radiofrequency magnetron sputtering using GaSb, GaTe, and Te targets. Prepared thin films are characterized by means of energy dispersive X-ray analysis coupled with a scanning electron microscope to determine the chemical composition and by variable angle spectroscopic ellipsometry to establish film thickness. Good agreement between results of calculations and experimentally determined compositions of the co-deposited thin films is achieved for both the above-mentioned tie-lines. Moreover, in spite of all the applied simplifications, the proposed model is robust to be generally used for studies where the influence of thin film composition on their properties is investigated.

The Structure of GaSbSe Glasses by High‐Resolution X‐Ray Photoelectron Spectroscopy

To understand the unique physical properties of GaSbSe glasses, high‐resolution X‐ray photoelectron spectroscopy (XPS) studies are performed on representative compositions within the glass‐forming region. The observed peaks in the valence band as well as in Ga, Sb, and Se core‐level XPS spectra are related to the main structural building blocks of the covalent network. On the basis of disproportionality equations and quantitative XPS analysis, the SeSeSe fragments are shown to exist in the glasses with 65 and 68 at% of Se, whereas the samples with lower Se content are shown to contain a significant concentration of SeSe bonds instead. Although the majority of Ga atoms are deemed to form fourfold coordinated units, the existence of Ga atoms in threefold coordination, those bonded to other metal, and forming Ga clusters of undissolved Ga are also plausible on the basis of Ga 3d XPS spectrum analysis. Partial or full destruction of antimony selenide pyramids is found in glasses with low Se content.

Epitaxial Growth of Optoelectronically Active Ga(As)Sb Quantum Dots on Al‐Rich AlGaAs with GaAs Capsule Layers

We present a study of optoelectronically active Ga(As)As quantum dots (QDs) on Al‐rich AlxGa1-xAs layers with Al concentrations up to x = 90%. So far, however, it has not been possible to grow optoelectronically active Ga(As)As QDs epitaxially directly on and in between Al‐rich barrier layers in the AlGaInAsSb material system. A QD morphology might appear on the growth front, but the QD‐like entities will not luminesce. Here, we use photoluminescence (PL) measurements to show that thin Al‐free capsule layers between Al‐rich barrier layers and the QD layers can solve this problem; this way, the QDs become optoelectronically active; that is, the dots become QDs. We consider antimonide QDs, that is, Ga(As)Sb QDs, either on GaAs for comparison or on AlxGa1-xAs barriers (x >10%) with GaAs capsule layers in between. We also discuss the influence of QD coupling both due to stress/strain from neighboring QDs and quantum‐mechanically on the wavelength of the photoluminescence peak. Due to their mere existence, the capsule layers alter the barriers by becoming part of them. Quantum dots applications such as QD semiconductor lasers for spectroscopy or QDs as binary storage cells will profit from this additional degree of design freedom.

Predicting quantum spin hall effect in graphene/GaSb and normal strain-controlled band structures

Graphene (Gr) has been demonstrated to be a two dimensional (2D) topological insulator (TI) with an opened spin–orbit coupling (SOC) energy gap at Dirac point. The extremely small energy gap, however, makes the predicted quantum spin Hall (QSH) effect difficult to be observed at room temperature. In present work, we propose an effective way to tune the energy gap of Gr by combining with GaSb. The intrinsic bulk gap of Gr reaches up to 125 meV and 116 meV in Gr/(Ga)Sb and Gr/Ga(Sb), respectively, which makes it available in practical applications. Moreover, the energy gap of Gr can be opened and increased to 147 meV in GaSb/Gr/GaSb by hydrogen passivation. The inverted band ordering and gapless edge states further demonstrate that our considered heterostructures possess QSH effect. Normal strain engineering leads to effective control and substantial enhancement of their energy gap and band inversion. Hexagonal boron nitride (h-BN) is also verified to be a suitable substrate to supporting films without destroying their QSH effect. Our results provide feasible platform to design Gr-based spintronics devices.

Structural, morphological and magnetic properties of GaSbMn/Si(111) thin films prepared by radio frequency magnetron sputtering

The structural, chemical and magnetic properties of GaSbMn thin films grown by Radio Frequency magnetron sputtering on Si (111) substrates, varying the growth temperature, were studied. X-ray diffraction analysis shows that the samples are polycrystalline with multiple phases, and their crystalline quality improves as the substrate temperature increases. A morphological study was carried out using transmission electron microscopy and scanning electron microscopy, revealing the formation of magnetic nanoparticles and precipitates, which depends on the growth temperature. The electronic structure of the films, studied by X-Ray Photoelectron Spectroscopy, exhibits a closely spaced doublet that arises from the spin-orbital coupling into Ga 2p, Sb 3d, and Mn 2p spectra. Measurements of Magnetization as function of temperature, performed in a low external magnetic field (0.05 T), revealed a ferromagnetic ordering from low temperatures to above room temperature, due to the existence of the multiphases GaSbMn, MnSb and GaMn. The magnetization loops taken at 5 K, 150 K, 298 K and 350 K, show that saturation magnetization depends on the sample preparation temperature. For the sample grown at 573.15 K, saturation magnetization decreases with increasing temperature from 5 to 350 K, while for the sample grown at 773.15 K, it is almost independent of temperature, due to the formation of MnSb and GaMn precipitates embedded into GaSb semiconductor matrix.

Crystallization behavior and electrical characteristics of Ga–Sb thin films for phase change memory

In this work, we investigated the structural and conductivity stability of Ga–Sb thin films for phase change memory (PCM). The mass density and thickness change are significant for stability and reliability of PCM. The Ga–Sb thin films were deposited on SiO2/Si (100) wafer using magnetron co-sputtering method. Phase identification revealed that nanoscale face center cubic structure GaSb and rhombohedral structure Sb formed in Ga–Sb thin films, the formation of phase Sb was more obvious in Ga20Sb80. Ga–Sb film exhibits an unusual behavior upon crystallization with less mass density and thickness change. The microstructure of Ga45Sb55 thin films improved their structural (density and film thickness) characteristics: the crystal growth of {111} and {110} oriented grains in Ga–Sb thin films is obvious, the grains growth in Ga45Sb55 thin films was more even and the bonding states in Ga–Sb thin films were more stable. In addition, the conductivity activation energy of Ga–Sb decreased with increasing Sb contents, thus the temperature stability of conductivity was improved. The structure transformation and conductivity activation energy of Ga–Sb phase change materials are in favor of mechanical stresses reduction and reliability enhancement of PCM. This study introduces the influence mechanism of structural and conductivity stability in Ga–Sb thin films and may provide reference for further testing in higher endurance performance phase change materials.

GaTe-Sb2Te3 thin-films phase change characteristics.

A radio frequency magnetron co-sputtering technique exploiting GaTe and ${\rm Sb}_2 {\rm Te}_3$Sb2Te3 targets was used for the fabrication of Ga-Sb-Te thin films. Prepared layers cover broad region of chemical composition (${\sim}{10.0 {-} 26.3}\,\, {\rm at.}$∼10.0-26.3at. % of Ga, ${\sim}{19.9 {-} 34.4}\,\, {\rm at.}$∼19.9-34.4at. % of Sb) while keeping Te content fairly constant (53.8-55.6 at. % of Te). Upon crystallization induced by annealing, large variations in electrical contrast were found, reaching a sheet resistance ratio of ${{R}_{\rm annealed}}/{{R}_{\rm as - deposited}}\;\sim{2.2} \times {{10}^{ - 8}}$Rannealed/Ras-deposited∼2.2×10-8 for the ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 layer. Phase transition from the amorphous to crystalline state further leads to huge changes of optical functions demonstrated by optical contrast values up to $|\Delta n| + |\Delta k| = {4.20}$|Δn|+|Δk|=4.20 for ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 composition.

Mid-infrared electroluminescence from type-II In(Ga)Sb quantum dots

There exists significant interest in the demonstration and development of alternative mid-infrared emitters, with future applications for thermal scene projection, low-cost infrared sensing, and possible long-wavelength quantum communication applications. Type-II In(Ga)Sb quantum dots grown in InAs matrices have the potential to serve as a viable material system for wavelength-flexible, mid-infrared sources. Here, we dramatically expand the range of potential applications of these mid-infrared quantum emitters through the demonstration of surface-emitting electrically pumped mid-infrared light-emitting diodes with active regions utilizing type-II In(Ga)Sb quantum dots. Two device structures were studied, the first iteration being a single In(Ga)Sb insertion layer within a simple PIN structure and the second being a design engineered for improved room temperature emission with the addition of lattice matched AlAsSb cladding at the anode to block electrons and five layers of In(Ga)Sb dots to increase the effective volume of active material. Samples were grown by molecular beam epitaxy and the electrical and optical properties for each design were characterized as a function of temperature.

Optical properties and dynamics of excitons in Ga(Sb, Bi)/GaSb quantum wells: evidence for a regular alloy behavior

Optical properties and carrier dynamics in 6.6, 10.4, and 14.4 nm wide Ga(Sb, Bi)/GaSb quantum wells (QWs) with ∼10%–11% of Bi were studied by photoluminescence (PL), time-resolved PL, and transient reflectivity. Experiments revealed that low temperature emission is strongly governed by the decay of excitonic population that undergoes weak localization on the QW potential fluctuations rather than the strong defect-like localization typically found for highly mismatched alloys. This statement is supported first by the nearly linear increase of the PL intensity with the excitation power, second, by the lack of the S-shape signature in the temperature-dependent PL studies, and third, the absence of a strong lifetime dispersion for excitons. The low-temperature intraband carrier relaxation time is established in the range of 14–19 ps, nearly independent on the well width, while the exciton lifetime exhibits a well width dependence, i.e. this time decreases from ∼265 ps, through ∼206 ps, to ∼147 ps with the increase of the QW width from 6.6 to 14.4 nm. Our results demonstrate that in contrast to other dilute bismide alloys, GaSbBi behaves as a regular alloy rather than as a highly-mismatched material.

Improved Mechanical and Electrical Properties of Phase-Change-Memory Ga-Sb Thin Films.

In this study, we focus on the mechanical and electrical properties of Ga-Sb thin films with different Sb contents; the corresponding improvement mechanism is also discussed. The phase-identification results prove that cubic GaSb phase and rhombohedral Sb phase exist in crystalline Ga-Sb thin films. Moreover, elemental Ga formed in small sizes around the boundary was observed. The resistance-temperature curves prove that the crystallization temperature (Tx) of Ga-Sb is 40 °C higher than that of Ge₂Sb₂Te5 (GST), and that Tx increased with increasing Ga content, while the resistance contrasts decreased. Consequently, the amorphous thermal stability of Ga-Sb is superior. Nanoindentation results prove that the hardness and elasticity modulus of Ga-Sb increases with increasing Ga content and is higher than that of GST thin films. In addition, structural investigation demonstrated that with different Ga contents, the hardness improvement of Ga-Sb thin films benefits from grain-size effects and the precipitation of elemental Ga in grain boundaries. Therefore, the ratio of Ga and Sb content has a different influence on the properties of both constituents. These findings indicate that binary Ga-Sb compositions are promising candidates for phase-change-memory applications.

Amorphous Ga–Sb–Se thin films fabricated by co-sputtering

Ternary chalcogenides of a Ga–Sb–Se system are prospective materials for potential applications in the field of infrared optics. This Letter deals with the optical properties and photosensitivity of Ga–Sb–Se thin films deposited by co-sputtering, enabling us to fabricate amorphous thin films outside the glass-forming region. The optical bandgap range of 1.92–1.35 eV with corresponding refractive indices at 1.55 µm ranging from 2.47 to 3.33 can be reliably covered using G a 2 S e 3 and S b 2 S e 3 targets. Furthermore, the prolonged irradiation by the near-bandgap light under the pure argon atmosphere leads to the irreversible photo-bleaching effect in fabricated films. The magnitude of this effect decreases monotonically with an increasing antimony content.

Effective ionic transport in AgI‐based Ge(Ga)–Sb–S chalcogenide glasses

AbstractAgI‐based Ge–Sb–S, Ga–Sb–S, and Ge–Ga–Sb–S chalcogenide glasses were designed and prepared by melt‐quenching, thereafter their thermal properties and conductive performance were comparatively investigated on the basis of their composition‐induced network structures. Glass transition in each sample was examined by DSC measurements. Results showed that the samples containing Ge had a higher thermal stability than the Ga–Sb–S–AgI sample, and the Ge–Sb–S–AgI sample obtained had the highest conductivity ion. Raman spectrum analysis was performed, and the results indicated that the [GeS4‐xIx] structural units and [SbS3−xIx] pyramids in the matrix produced effective ion transport channel for dissolved conductive Ag+ ions. In the matrix containing Ga, the [Ga(Ge)S4‐xIx] structure was consumed by part of [S3Ga–GaS3] ethane‐like units, which had no contribution to the ion transition framework. The study provided the directions for composition and structure configuration control in effective conductive chalcogenide glasses.

AlxGa1–xSb Crystals Grown by a Modified Stepanov Technique with an Ultrasonic Effect

A modified Stepanov method with a floating crucible and ultrasound effect was developed for the growth of AlxGa1–xSb solid solution crystals. In this modified method, the Stepanov technique with a graphite die prevented Al oxidation on the melt surface, a floating crucible separated the Ga–Sb melt and Al–Ga–Sb source, and ultrasound at a frequency of 10 kHz provided introduction of the source into the melt. The segregation coefficients and activity coefficients of Al and Ga were calculated and used for the growth of AlxGa1–xSb crystals. The segregation coefficients of Al and Ga decreased with the increase of Al concentration, which could be the result of increased activity of Sb. We demonstrated that the ultrasound with the power of 60 and 75 W provided feeding of the source into the melt through a hole with a 2 mm diameter in the bottom of the floating crucible. The introduction of the Al–Ga–Sb source into the Ga–Sb melt increased the Al concentration in a pulled AlxGa1–xSb crystal from 50% to 67%. The h...

Realizing a stable high thermoelectric zT ∼ 2 over a broad temperature range in Ge1−x−yGaxSbyTe via band engineering and hybrid flash-SPS processing

We report a remarkably high and stable thermoelectric zT ∼ 2 by manipulating the electronic bands in hybrid flash-SPSed Ga–Sb codoped GeTe.

Formation of a Thin Continuous GaSb Film on Si(001) by Solid Phase Epitaxy.

Nanocrystalline GaSb films were grown on Si(001) from the stoichiometric Ga–Sb mixture using solid-phase epitaxy at temperatures of 200–500 °C. Use of the solid-phase epitaxy method allowed the suppression of Ga surface diffusion and prevention of intense Sb desorption. At the annealing temperature of 300 °C, a 14-nm-thick GaSb film aggregates, while a 20-nm-thick GaSb film remains continuous with a roughness of 1.74 nm. A GaSb film with a thickness of 20 nm consists of crystalline grains with a size of 9–16 nm. They were compressed by ~2%. For some GaSb grains, new epitaxial relationships have been found: GaSb||Si and GaSb||Si, GaSb||Si and GaSb||Si, and GaSb||Si and GaSb||Si.

Ion irradiation effects on Sb-rich GaSb films

Here we show the formation of amorphous, non-stoichiometric GaSb films by magnetron sputtering and the ion irradiation effects on the films. GaSb films in the 20–300 nm thickness range were deposited by magnetron sputtering on SiO2/Si substrates at room temperature and subsequently irradiated with 17 MeV Au+7 ions at different fluences. Structural, compositional, and morphological characterizations were performed by means of x-ray diffraction, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, scanning electron microscopy and x-ray absorption fine structure analyses. We could verify that, throughout the above-mentioned thickness range, films were amorphous, with excess Sb to the ratio 1:2 (Ga:Sb). The initially compact films attained a foam-like structure after irradiation, with significant swelling that is dependent on the initial film thickness: the thicker the film, the more it swelled. The excess Sb attained different oxidation states depending on film thickness and this influenced the final density of the films, thus influencing the swelling. The local atomic structure around Ga atoms was also investigated, revealing a decrease in Ga–Sb scattering contribution with increasing irradiation fluence, at the same time as the increase in Ga–O scattering for irradiation fluence above 1 × 1014 at/cm2 (inclusive).