X-ray Pole Figure Research Articles

Phase degradation in BxGa1−xN films grown at low temperature by metalorganic vapor phase epitaxy

Using metalorganic vapor phase epitaxy, a comprehensive study of BxGa1−xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750–900°C and 20Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to ~7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stacking faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at ~362nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. Only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.

Van der Waals epitaxy of CdTe thin film on graphene

van der Waals epitaxy (vdWE) facilitates the epitaxial growth of materials having a large lattice mismatch with the substrate. Although vdWE of two-dimensional (2D) materials on 2D materials have been extensively studied, the vdWE for three-dimensional (3D) materials on 2D substrates remains a challenge. It is perceived that a 2D substrate passes little information to dictate the 3D growth. In this article, we demonstrated the vdWE growth of the CdTe(111) thin film on a graphene buffered SiO2/Si substrate using metalorganic chemical vapor deposition technique, despite a 46% large lattice mismatch between CdTe and graphene and a symmetry change from cubic to hexagonal. Our CdTe films produce a very narrow X-ray rocking curve, and the X-ray pole figure analysis showed 12 CdTe (111) peaks at a chi angle of 70°. This was attributed to two sets of parallel epitaxy of CdTe on graphene with a 30° relative orientation giving rise to a 12-fold symmetry in the pole figure. First-principles calculations reveal that, despite the relatively small energy differences, the graphene buffer layer does pass epitaxial information to CdTe as the parallel epitaxy, obtained in the experiment, is energetically favored. The work paves a way for the growth of high quality CdTe film on a large area as well as on the amorphous substrates.

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.

Ultrasonic studies of texture inhomogeneities in pressure vessel steel subjected to ultrasonic impact treatment and shock compression

Abstract Specimens of Cr-Ni-Mo-V pressure vessel steel 15Kh2NМFА were cut from the achieve wall of the WWER-1000 reactor and were then deformed either using ultrasonic impact treatment (UIT) inducing low energy multiple impacts or by drop-hammer inducing high energy shock compression (HESC). With the aim of texture evaluation comprehensive ultrasonic measurements and X-ray texture analysis were carried out in different sections of the deformed specimens. A nondestructive quantitative analysis of the crystallographic texture in various layers of the deformed specimens was performed on the base of precise measurements of the bulk-wave ultrasonic velocities ( v ij ) by means of the pulse-echo method using a home-made automated apparatus. The mass densities ( ρ ) of the deformed specimens and their cut sections were also precisely measured. The obtained data allowed calculating orientation distribution coefficients ( W 4 i 0 ) of crystallites and to construct ultrasonic pole figures for different specimen layers and cut sections. The ultrasonic pole figures correlate well to the X-ray pole figures registered in the cut sections of the specimens. It is found that maximal pole intensities (Δ I [ ijk ] ) and spatial inhomogeneities of these textures depend on the used regimes of UIT and HESC. The revealed peculiarities of the texture formation correlate well to the depth distributions of microhardness and strain extents. The higher the strain extent or the longer the treatment time, the more intensive texture is registered and the deeper the textured layer is observed. The ultrasonic method applied is shown to be useful and efficient for non-destructive examination of elastically heterogeneous systems, particularly the materials with mechanically treated surfaces.

Epitaxial growth and transport property of La0.9Sr0.1MnO3 thin films deposited on MgO, LaAlO3 and SrTiO3 substrates

La0.9Sr0.1MnO3 (LSMO) thin films were grown on (100)-oriented MgO, LaAlO3 and SrTiO3 substrates by pulsed laser deposition, so as to investigate the effect of substrate-induced lattice mismatch on epitaxial growth, electrical resistivity and transport behavior of the films. The X-ray diffraction patterns and pole figures indicated that the LSMO thin films were epitaxially grown on the three kinds of substrate, and the orientation relationship was found to be LSMO (100) [010]//substrate (100) [010]. The measurement of electrical resistivity showed that the LSMO thin films were characteristic of semiconductor, and the transport mechanism was dominated by the small polaron hopping (SPH) model. Compared with MgO and LaAlO3 substrates, the LSMO thin films grown on SrTiO3 substrate exhibited lower resistivity and smaller conductivity hopping energy, due to the less lattice mismatch at film/substrate interface which tended to reduce the Jahn-Teller distortion and thus the localization of charge carriers was decreased.

Pole figure measurement of the initial growth of GaN nanoneedles on GaN/Si(111) by using hydride vapor phase epitaxy

We report on crystallographic analyses of one-dimensional GaN nanoneedles grown on a n-GaN epilayer by using hydride vapor phase epitaxy. The nanoneedles were grown with a HCl:NH3 gas flow ratio of 1:38 at 600 °C. The growth time of the GaN nanoneedles affected their morphologies. As time progressed, GaN dots nucleated and then evolved as nanoneedles. The vertical growth rate of GaN nanoneedles was higher than the lateral growth rate under optimized growth conditions. X-ray pole figure measurements were carried out using a four-axis diffractometer. For the sample grown for 20 min, we obtained discrete patterns with six strong dots and weak dough-nut and cotton swab patterns, indicating that most of the nanoneedles were grown ideally, but partially, in the x-y plane with an azimuthal rotation angle ϕ = 15 ~ 45° rotated to the substrate, and a few GaN nanoneedles were tilted by ±4° or by more than 32° from the vertical c-axis.

Surface Structure Engineering of Cu Thin Films for Electrochemical CO2 Reduction

Global dependence on fossil fuels as energy sources and the alarming increase of greenhouse gas emissions has necessitated the development of carbon-free and carbon-neutral renewable energy sources for the future. The sequestration of CO2 emissions along with subsequent electrochemical reduction into fuel products, forms a carbon-neutral synthetic fuel cycle which could potentially be streamlined into existing fuel infrastructures. To date, only Cu has displayed any propensity as a catalyst to electrochemically reduce CO2 into longer chain hydrocarbons. Previous studies on Cu single crystals have shown large facet sensitivities for electrochemical CO2reduction product selectivity. The aim of our research is to utilize these surface structure motifs to design active and selective catalysts that are amenable to device integration. To this end, we use physical vapor deposition to synthesize Cu thin films in both low and high Miller index orientations for electrochemical CO2 reduction. X-ray pole figures demonstrate that Cu thin films can be epitaxially grown in the <100>, <111>, and <751> orientations by utilizing the orientation of the single crystal substrate. The different Cu thin film orientations were tested for their CO2 reduction activity and selectivity using electrochemical measurements in tandem with gas phase (gas chromatography) and liquid phase (nuclear magnetic resonance) product detection methods. Here, we will demonstrate how surface structure engineering can guide selectivity for C-C coupling and oxygenate formation during electrochemical CO2 reduction.

Inhomogeneous Spin Diffusion in Thickness-Controlled La 0 . 6 7 Sr 0 . 3 3 MnO 3 /YBa 2 Cu 3 O 7 − δ /La 0 . 6 7 Sr 0 . 3 3 MnO 3 Trilayers

La0.67Sr0.33MnO3/YBa2Cu3O7 − δ /La0.67Sr0.33 MnO3 (LSMO/YBCO/LSMO) trilayers are prepared on single-crystal LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) with the thicknesses of LSMO layers fixed at 50 nm, and the thickness of YBCO sandwich varied from 10 to 40 nm. X-ray diffraction (XRD) and pole figure measurements disclose that all the trilayers are c-oriented and there is little change in the textures of YBCO layer for both in-plane and out-of-plane. Based on inductive, transport, and magnetic measurements, obvious suppression of superconductivity with a decrease in YBCO thickness is observed, particularly at thickness below 20 nm. Importantly, there are great disparities in the superconducting transition temperature (T c) and transition width (ΔT c) values for both inductive and transport measurements. The T c values from an inductive method are much smaller than those from transport measurements, with ΔT c in the opposite direction. The results are explained by the nonuniform diffusion of spin-polarized quasiparticles due to the comparable length scales of the spin diffusion length and the superconducting film thickness.

Structural, magnetic and optical properties of Y bFe2O4 films deposited by spin coating

Rare-earth iron oxides (RFe2O4) have attracting attention as new electronic device materials because of their numerous functionalities, such as electronic ferroelectricity, ferrimagnetism, and high infrared absorption. In this paper, nearly monophasic Y bFe2O4 films were prepared on α-Al2O3(001) substrates by the spin coating method using an aqueous-based Y bFe2O4 solution. The solution was composed of a stoichiometric ratio of Y b(CH3COO)3 and Fe(NO3)3 with excess chelating agents. After heat treatment above 800 °C, well-crystallized and highly (001)-oriented Y bFe2O4 started to epitaxially form on the substrate under controlled oxygen partial pressure with H2/CO2 gas mixtures. X-ray pole figure analysis confirmed the following epitaxial relationship: Y bFe2O4[100](001)//α-Al2O3[100](001). Moreover formation of an Fe3O4 interracial layer between Y bFe2O4 and α-Al2O3 was detected by high-resolution transmission electron microscopy. Presence of the Fe3O4 interracial layer seemed to release the lattice misfit with the substrate. The Fe2+/Fe3+ ratio in the obtained Y bFe2O4 films was nearly stoichiometric and the indirect bandgap assigned to Fe2+ → Fe3+ charge transfer excitation was found to be ∼0.4 eV by optical spectroscopy. A clear magnetic transition from the paramagnetic state to the ferrimagnetic state occurred at ∼230 K.

Control of Preferential Orientation of La&lt;sub&gt;1-x&lt;/sub&gt;Sr&lt;sub&gt;x&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Thin Films by Pulsed Laser Deposition

La1-xSrxMnO3 (LSMO) thin films were grown on (100)- and (110)-oriented MgO substrates by pulsed laser deposition, so as to control the preferential orientation of the films. At the optimum deposition temperature (Td = 923K), LSMO thin films with a dense texture and a smooth surface were prepared. The XRD patterns and X-ray pole figures indicated that the LSMO thin films were epitaxially grown on MgO substrates, due to the small lattice mismatch between the films and substrates The possible orientation relationships were found to be LSMO (100) [100] // MgO (100) [100] and LSMO (110) [110] // MgO (110) [110], as for the (100) and (110) MgO substrates, respectively.

Nanometer-Thick Gold on Silicon as a Proxy for Single-Crystal Gold for the Electrodeposition of Epitaxial Cuprous Oxide Thin Films.

Single-crystal Au is an excellent substrate for electrochemical epitaxial growth due to its chemical inertness, but the high cost of bulk Au single crystals prohibits their use in practical applications. Here, we show that ultrathin epitaxial films of Au electrodeposited onto Si(111), Si(100), and Si(110) wafers can serve as an inexpensive proxy for bulk single-crystal Au for the deposition of epitaxial films of cuprous oxide (Cu2O). The Au films range in thickness from 7.7 nm for a film deposited for 5 min to 28.3 nm for a film deposited for 30 min. The film thicknesses are measured by low-angle X-ray reflectivity and X-ray Laue oscillations. High-resolution TEM shows that there is not an interfacial SiOx layer between the Si and Au. The Au films deposited on the Si(111) substrates are smoother and have lower mosaic spread than those deposited onto Si(100) and Si(110). The mosaic spread of the Au(111) layer on Si(111) is only 0.15° for a 28.3 nm thick film. Au films deposited onto degenerate Si(111) exhibit ohmic behavior, whereas Au films deposited onto n-type Si(111) with a resistivity of 1.15 Ω·cm are rectifying with a barrier height of 0.85 eV. The Au and the Cu2O follow the out-of-plane and in-plane orientations of the Si substrates, as determined by X-ray pole figures. The Au and Cu2O films deposited on Si(100) and Si(110) are both twinned. The films grown on Si(100) have twins with a [221] orientation, and the films grown on Si(110) have twins with a [411] orientation. An interface model is proposed for all Si orientations, in which the -24.9% mismatch for the Au/Si system is reduced to only +0.13% by a coincident site lattice in which 4 unit meshes of Au coincide with 3 unit meshes of Si. Although this study only considers the deposition of epitaxial Cu2O films on electrodeposited Au/Si, the thin Au films should serve as high-quality substrates for the deposition of a wide variety of epitaxial materials.

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.

Epitaxial growth of Sc2O3 films on Gd2O3-buffered Si substrates by pulsed laser deposition

We investigated the optimal conditions to prepare high-quality Sc2O3 films on Gd2O3-buffered Si wafers using pulsed laser deposition technique with an aim at developing waveguide devices that can transform the performance of the gradient echo quantum memory based on bulk crystals. Under the optimal conditions, only oxide and Si (2 2 2) peaks appeared in the X-ray diffraction pattern. The Sc2O3 (2 2 2) diffraction peak was located at 2θ = 31.5° with a full width at half maxima (FWHM) of 0.16°, and its rocking curve had a FWHM of 0.10°. In-plane epitaxial relationship was confirmed by X-ray pole figure where Sc2O3 (1 1 1) was parallel to Si (1 1 1). High-resolution TEM images indicated clear interfaces and perfect lattice images with sharp electron diffraction dots. All these results confirm that the oxide films on Si were single crystalline with high quality.

Large Single Crystal SnS2 Flakes Synthesized from Coevaporation of Sn and S

Remarkable properties of layered metal dichalcogenides and their potential applications in various fields have raised intense interest worldwide. We report tens of microns-sized ultrathin single crystal SnS2 flakes grown on amorphous substrates using a simple one-step thermal coevaporation process. X-ray pole figure analysis reveals that a majority of flakes are oriented with the (0001) plane parallel to the substrate and a preferred fiber texture. For few-layer-thick SnS2, Moire patterns of 6-fold and 12-fold symmetries are observed by transmission electron microscopy imaging and diffraction. These patterns result from the relative rotation between SnS2 layers in the ultrathin flake. The 12-fold symmetry is consistent with a known quasicrystal pattern. The photoluminescence spectrum supports that these ultrathin flakes possess a direct bandgap. Carrier lifetime measured by time-resolved photoluminescence of a single flake is a few nanoseconds. These results improve our understanding of the formation and ...

Effect of extrusion and annealing on the mechanical and corrosion properties of the magnesium alloys

Event Abstract Back to Event Effect of extrusion and annealing on the mechanical and corrosion properties of the magnesium alloys Zhigang Xu1, Sergey Yarmolenko1 and Jag Sankar1 1 North Carolina A&T State University, NSF ERC for Revolutionizing Metallic Biomaterials, United States Introduction: Mg-based alloys have shown remarkable advantages serving as biodegradable implant materials due to their excellent biocompatibility, closer elastic modulus to natural bone, and inherent biodegradation capability [1],[2]. However, the fast corrosion of Mg in the physiological system with high chloride concentration prevents its success in many biomedical applications. Recently, Mg-rare earth (RE)-based alloys gained a great deal of attention because these materials normally exhibit high strength and ductility, and the best corrosion performance [3]. In this project, the focus was placed on the study the effects of extrusion and post heat treatment on the texture development, mechanical and corrosion properties of Mg-RE-based alloys. Materials and Methods: Mg-1.0Zn-0.3Ca-1.5REs alloy was melted and cast under the protection of argon gas in a glove box. Solution treatment (T4) was performed at 500°C for 12 hours. Samples after T4 treatment were extruded at 400 °C with an extrusion ratio of 10. Heat treatments, i.e. annealing of the extruded alloy were carried out at temperatures of 250 ºC, 300 ºC, 350 ºC, 400 ºC, 450 ºC and 500 ºC, respectively, with a holding time of an hour. The microstructures of the as-extruded and annealed materials were observed with SEM. Their textures were determined with X-ray pole figures. The mechanical and corrosion properties were assessed with microhardness and electrochemical impedance spectroscopy (EIS). Results and Discussion: Fig. 1. Shows the microstructure of the as-extruded and the annealed alloys. In the as-extruded condition, the alloy has a grain size of ~5 µm. As shown in Fig.1 and 2, low temperature annealing at 250 ºC and 300 ºC only causes marginal grain growth and second phase dissolving. With the increased annealing temperature, both the grain growth and second phase dissolving become significant. EIS studies shows a general trend that with the increasing of the annealing temperature, the corrosion resistance was increased (as shown in Fig. 3.). Using X-ray pole figure method, MAX values which represent the texture intensity of each material were obtained and are shown in Fig. 4. As-extruded alloy had strong texture with MAX value 20.3. Annealing of for an hour at temperature 150°C below the extrusion temperature led to reduction of texture intensity about two (2) times due to recrystallization. Annealing for an hour at extrusion temperature left only one fourth of texture intensity. At temperatures higher than extrusion process, the texture almost disappeared and cannot be evaluated by pole figure due to insufficient statistics in the material with overgrown grains. Fig. 5 shows the microhardness in the cross-section plane of the as-extruded and annealed samples. Small grain size, the precipitation of the second phase particles plus high defect density produced the highest hardness in as-extruded state. Annealing at different temperatures led to different degrees of grain growth, second phase dissolving and defect alleviation. These changes may explain the non-linear reduction of the microhardness. Conclusion: The experiments revealed that extrusion leads to highly textured and small grain-sized microstructure of the Mg-Zn-RE based alloy. Annealing dissolves the second phase into the Mg-matrix, leading to grain growth to different extents depending to the annealing temperature. In general, the corrosion resistance of the materials is enhanced by annealing, while the microhardness weakened by the same process. The research was financially supported by the USA NSF sponsored Engineering Reseach Center of Revolutionizing Metallic Biomaterials.

Role of Crystallographic Texture and Crystallinity on the Electrochemical Behavior of Nanocrystalline Sr Doped Calcium Phosphate Coatings

In order to decipher the effect of crystallite size and crystallographic texture on the electrochemical properties of strontium doped calcium phosphate (CaP) coatings, electrodeposition was carried out on two different substrates (Ti and NiTi) and at two different current densities (−1.5 and −3.5 mA cm−2). X-ray diffraction (XRD) studies confirmed the presence of brushite and hydroxyapatite (HaP) phases in varying weight fraction as an effect of varying current densities. XRD line profile analyses showed crystallite size of both CaP phases decrease with increase in current density. X-ray pole figures revealed preferential orientation (texture) of HaP crystallites in [0001] direction and it is pronounced at higher current density for both substrates. Surface characterization and phase analysis were carried using scanning electron microscopy and transmission electron microscopy (TEM). TEM results corroborate the local texture of HaP crystallites, where arc diffraction pattern of (0002) facet was observed. Polarization studies revealed that coating synthesized at higher current density on NiTi having high degree of texture showed icorr of 10−8 A cm−2, which is one order less than that of values obtained for other coatings (10−7 A cm−2). Electrochemical impedance spectroscopy studies exhibited two relaxation features, suggesting the formation of inner barrier and outer porous layer.

Formation of preferentially oriented Y3Al5O12 film on a reactive sapphire substrate: Phase and texture transitions from Y2O3

Yttrium aluminum garnet (Y3Al5O12, YAG) thin films were synthesized by reacting sol–gel derived Y2O3 <111>-oriented films with sapphire substrates. Phase development and inheritance of crystallographic orientation during the formation of YAG was investigated. The major sequence of the phase development from Y2O3 to YAG with increasing temperature was Y2O3→hexagonal yttrium aluminate (YAlO3, YAH)→YAG, showing that the diffusion of Al3+ into Y2O3 films occurred. The highly {101¯1} -textured YAH phase, which was first synthesized in the present study, would inherit the preferred {111} plane of self-textured Y2O3 with structural similarity. The YAG phase also showed highly preferred <211> orientation (Lotgering’s factor, F=0.57) only when the films were prepared on the sapphire (0001) substrate. X-ray pole figure and electron backscatter diffraction results suggested an epitaxial growth of {211}-textured YAG, which was supported by the consideration of lattice matching between the planes of YAG (211) and sapphire (0001).

Effect of substrates and surfactants over the evolution of crystallographic texture of nanostructured ZnO thin films deposited through microwave irradiation

In spite of intense research on ZnO over the past decade, the detailed investigation about the crystallographic texture of as obtained ZnO thin films/coatings, and its deviation with growth surface is scarce. We report a systematic study about the orientation distribution of nanostructured ZnO thin films fabricated by microwave irradiation with the variation of substrates and surfactants. The nanostructured films comprising of ZnO nanorods are grown on semiconductor substrates such as [Si(100), Ge(100)], conducting substrates (ITO-coated glass, Cr coated Si), and polymer coated Si (PMMA/Si) to examine the respective development of crystallographic texture. The ZnO deposited on semiconductor substrates yields mixed texture, whereas c-axis oriented ZnO nanostructured films are obtained by conducting substrate, and PMMA coated Si substrates. Among all the surfactants, nanostructured film produced by using the lower molecular weight of polymeric surfactants (polyvinylpyrrolidone) shows a stronger (0002) texture, and that can be tuned to 10-1̅0 by increasing the molecular weight of the surfactant. The strongest basal pole is achieved for the ZnO deposited on PMMA coated Si as substrate, and cetyl-trimethyl ammonium bromide as cationic surfactant. The texture analysis is carried out by X-ray pole figure analysis using the Schultz reflection method.

Texture of Ge on SrTiO3 (001) substrates: Evidence for in-plane axiotaxy

We report the first experimental evidence of the formation of an axiotaxial texture in a semiconductor/oxide structure, namely Ge deposited by molecular beam epitaxy on a SrTiO3 substrate. The texture of the deposit is carefully analyzed based on X-ray pole figure measurements. We show in particular that the axiotaxial texture is not random, but that the deposit presents a limited number of well defined crystal orientations along axiotaxy locus. We also evidence the presence of twinned zones in the Ge crystal, and we discuss their experimental signature regarding that of the axiotaxy texture. In the end, we show that interface dangling bonds are the main parameter driving Ge crystal orientation, and we compare their influence to that of epitaxial misfit.

Biaxially oriented CdTe films on glass substrate through nanostructured Ge/CaF2 buffer layers

Heteroepitaxial CdTe films were grown by metal organic chemical vapor deposition on glass substrates through nanostructured Ge/CaF2 buffer layers which were biaxially oriented. It allows us to explore the structural properties of multilayer biaxial semiconductor films which possess small angle grain boundaries and to test the principle of a solar cell made of such low-cost, low-growth-temperature semiconductor films. Through the x-ray diffraction and x-ray pole figure analysis, the heteroepitaxial relationships of the mutilayered films are determined as [111] in the out-of-plane direction and 〈10〉CdTe//〈10〉Ge// in the in-plane direction. The I–V curves measured from an ITO/CdS/CdTe/Ge/CaF2/glass solar cell test structure shows a power conversion efficiency of ∼η = 1.26%, illustrating the initial success of such an approach. The observed non-ideal efficiency is believed to be due to a low shunt resistance and high series resistance as well as some residual large-angle grain boundary effects, leaving room for significant further improvement.