Solid Phase Epitaxy Research Articles

Generation of shallow nitrogen-vacancy centers in diamond with carbon ion implantation

The shallow nitrogen-vacancy center of diamond exhibits excellent sensitivity and resolution in the magnetic detection and quantum sensing areas. Compared with other methods, low-energy carbon ion implantation does not need high-purity diamond nor introduce new impurity atoms, but the formation mechanism of nitrogen-vacancy center is not clear. In this work, shallow nitrogen-vacancy centers are created in the diamond by low energy carbon ion implantation and vacuum annealing, and the transformation mechanism of nitrogen-vacancy centers in diamond is studied by Raman spectroscopy, X-ray photoelectron spectroscopy, and positron annihilation analysis. The results show that shallow nitrogen-vacancy centers can be obtained by carbon ion implantation combined with vacuum annealing. After implantation, superficial layer of diamond shows the damage zone including lattice distortion and amorphous carbon, and carbon-vacancy cluster defects (carbon atoms are surrounded by vacancy clusters) are generated. In the vacuum annealing process, the damaged area gradually transforms into the diamond structure through the recovery of the distortion area and the solid-phase epitaxy of the amorphous carbon area, accompanied by the continuous dissociation of carbon-vacancy cluster defects. When samples are annealed at 850 and 900 ℃, the structure of the damaged area is partially repaired. While annealing at 950 ℃, not only the damaged layer is basically recovered, but also nitrogen atoms capture the single vacancy obtained by the dissociation of carbon vacancy clusters, forming the nitrogen-vacancy centers.

Heteroepitaxial Growth of a Ta3N5 Thin Film with Clear Anisotropic Optical Properties.

Ta3N5 is a promising semiconductor photocatalyst which can generate H2 gas from water under visible light illumination. It is expected that Ta3N5 exhibits a strong anisotropy in its physical properties stemming from its highly anisotropic crystal structure. However, such anisotropic properties have not been verified experimentally due to the difficulty in synthesizing a large single crystal. Here, we report the synthesis of (010)-oriented Ta3N5 single-crystalline thin films by solid phase epitaxy on the (110) plane of perovskite LaAlO3 substrates. The obtained epitaxial thin films of Ta3N5 exhibited clear optical anisotropy (pleochroism) as predicted by previous first-principles calculations. The optical gap for E||[100] polarization (∼2.12 eV) was smaller than that for E||[100] polarization (∼2.27 eV).

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3(001).

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich films with different stoichiometry ( and ) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/FeO bilayers deposited before on Nb-doped SrTiO(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of cations in the low-spin state on octahedral sites for the film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements.

The magnetic properties of Mn5Ge3 thin films grown on PMN-PT

The authors report the thickness dependent structural and magnetic properties of Mn5Ge3 thin films with different Mn layer thicknesses in the range from 5 nm to 30 nm deposited on Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) substrates using solid phase epitaxy. Gradual decrease of the surface roughness due to the formation of larger grains, as well as the decrease of the coercivity and squareness ratio on increasing of Mn layer thickness has been observed. It has been revealed that the slightly greater value of the saturation magnetization than the corresponding one observed early for thin films and bulk samples isassociated withthe presence ofstructural defects. The ferromagnetic resonance (FMR) spectra have been obtained to be isotropic for the films with 5 nm thickness, whereas those registered from the films with the thicknesses of 10 nm and above demonstrated in-plane magnetic anisotropy, which have been interpreted as to be resulted from magnetocrystalline anisotropy as well as the stress-induced magnetic anisotropy. These results are suggested to create a major interest in the development of magnetoelectric heterostructured devices based on strain coupling that are compatible with CMOS technology.

Solid-phase epitaxial growth of the correlated-electron transparent conducting oxide SrVO3

$\mathrm{SrV}{\mathrm{O}}_{3}$ thin films with a high figure of merit for applications as transparent conductors were crystallized from amorphous layers using solid phase epitaxy (SPE). Epitaxial $\mathrm{SrV}{\mathrm{O}}_{3}$ films crystallized on $\mathrm{SrTi}{\mathrm{O}}_{3}$ using SPE exhibit room-temperature resistivities as low as $5.2\ifmmode\times\else\texttimes\fi{}{10}^{--5}$ and $2.5\ifmmode\times\else\texttimes\fi{}{10}^{--5}\phantom{\rule{0.16em}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$, residual resistivity ratios of 2.0 and 3.8, and visible light transmission maxima of 0.89 and 0.52 for film thicknesses of 16 and 60 nm, respectively. $\mathrm{SrV}{\mathrm{O}}_{3}$ layers were deposited at room temperature using radiofrequency sputtering in an amorphous form and subsequently crystallized by heating in a controlled gas environment. The lattice parameters and mosaic angular width of x-ray reflections from the crystallized films are consistent with partial relaxation of the strain resulting from the epitaxial mismatch between $\mathrm{SrV}{\mathrm{O}}_{3}$ and $\mathrm{SrTi}{\mathrm{O}}_{3}$. A reflection high-energy electron diffraction study of the kinetics of SPE indicates that crystallization occurs via the thermally activated propagation of the crystalline/amorphous interface, like SPE phenomena in other perovskite oxides. Thermodynamic calculations based on density functional theory predict the temperature and oxygen partial pressure conditions required to produce the $\mathrm{SrV}{\mathrm{O}}_{3}$ phase and are consistent with the experiments. The separate control of deposition and crystallization conditions in SPE presents possibilities for the crystallization of transparent conductors in complex geometries and over large areas.

Ion beam-assisted solid phase epitaxy of SiGe and its application for analog memristors

Low dimensional defects such as dislocation in single crystal Si are known to serve as a fast diffusion path of metal ions. Recently, many efforts have been made to employ dislocations in single crystal based oxide and silicon as reliable Ag filaments in CBRAM (Conductive Bridge Resistive Memory). In this study, we report the synthesis of the SiGe epitaxy thin films by an ion beam-assisted solid phase epitaxy process and its application for analog CBRAM memristors. The epitaxial SiGe thin films were produced by implanting Ge ions into a LPCVD a-Si film, followed by post annealing. We found that the interface oxide between a-Si and c-Si hinders facile epitaxy growth of a-Si. Thus, the ion implantation parameters were carefully adjusted to effectively remove the interface oxide and produce the epitaxy thin films of high quality. The low dimensional defects, identified to be a stacking fault by TEM observations, were observed to be densely located near the surface region of the SiGe epitaxy thin film. We fabricated the CBRAM devices by sandwiching the epitaxial Si thin films between an active metal electrode of Ag and a heavily doped Si wafer. We investigated the performances of the CBRAM devices and discuss the effect of the low dimensional defects on the switching behaviors of the devices. We found that the Ge implantation enables forming-free CBRAM operation and also provides reduced variations in set and reset voltages. Furthermore, we performed the feasibility study on the use of the epitaxial Si based CBRAM for artificial synapse for neuromorphic computing.

Epitaxial Ge-Gd[formula omitted]O[formula omitted] on Si(111) substrate by sputtering for germanium-on-insulator applications

Germanium-on-insulator (GeOI) technology is a potential-alternative to the bulk-silicon based devices for radio-frequency (RF), and complementary metal oxide semiconductor applications at advanced technology nodes. A thin germanium channel is the key enabler of high mobility transistors and group-IV photonic devices. A prohibitive cost of GeOI wafers may discourage high volume manufacturing (HVM) despite promising performance. Here, we demonstrate epitaxial Gd2O3-Ge-Gd2O3 thin film growth on Si(111) substrate in an HVM platform - RF magnetron sputter system, where, the first Gd2O3 layer acts as buried-oxide (BOX) in the GeOI wafer. The second Gd2O3 layer is used as a cap-layer to be removed later using wet etching. Both the Gd2O3 layer is grown epitaxially at 750∘C, while the germanium layer is grown at room temperature and crystallised later by solid phase epitaxy (SPE) technique. The entire growth is performed without vacuum-break, to enable high throughput and excellent interface control. To compare the quality of the heterostructure, this sputter based SPE is performed on: (1) in-situ sputter grown, versus (2) ex-situ molecular-beam-epitaxy (MBE) grown epitaxial Gd2O3 BOX layer. The x-ray diffraction analysis confirms the formation of twin-free epitaxial Ge layer in the case of in-situ sputtered Gd2O3 while twinned Ge layer is observed in the case of ex-situ MBE grown Gd2O3. The twinning of the Ge layer in the ex-situ process is further supported by transmission electron microscopy analysis. Finally, we have performed an experiment to study the impact of Gd2O3 BOX layer thickness on the crystal quality of Ge layer and show that the Ge layer crystal quality remains intact irrespective of BOX layer thickness. Therefore, we have achieved twin free Ge epitaxy in RF magnetron sputter system, equivalent to in-situ All-MBE SPE process. Such a process enables low-cost GeOI wafer manufacturing for cost-effective RF transistors.

Strong magnetization and anisotropy of Mn5Ge3 thin films on Ge(001)

We report on the growth of Mn5Ge3 thin films on Ge(001) substrates following two methods: solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE). We have varied the thickness of the films, in order to study the magnetization and anisotropy evolution. A strongly enhanced magnetization of 1580 kA m−1, compared to 1200 ± 150 kA m−1 for films grown on Ge(111), has been measured on ultrathin films of 5 nm grown by RDE. Thicker films exhibited magnetizations <750 kA m−1. The films grown by SPE also exhibit strong magnetization of 1490 kA m-1 and a drop of magnetization by increasing the film thickness. The effective magnetic anisotropy exhibits a more complex behavior: increases on the SPE films and decreases on the RDE films while increasing the thickness of the films. Magnetostatic and interfacial anisotropies were considered and calculated. The results are discussed in terms of the growth methods and microstructure of the films.

Instrument for in situ hard x-ray nanobeam characterization during epitaxial crystallization and materials transformations.

Solid-phase epitaxy (SPE) and other three-dimensional epitaxial crystallization processes pose challenging structural and chemical characterization problems. The concentration of defects, the spatial distribution of elastic strain, and the chemical state of ions each vary with nanoscale characteristic length scales and depend sensitively on the gas environment and elastic boundary conditions during growth. The lateral or three-dimensional propagation of crystalline interfaces in SPE has nanoscale or submicrometer characteristic distances during typical crystallization times. An in situ synchrotron hard x-ray instrument allows these features to be studied during deposition and crystallization using diffraction, resonant scattering, nanobeam and coherent diffraction imaging, and reflectivity. The instrument incorporates a compact deposition system allowing the use of short-working-distance x-ray focusing optics. Layers are deposited using radio-frequency magnetron sputtering and evaporation sources. The deposition system provides control of the gas atmosphere and sample temperature. The sample is positioned using a stable mechanical design to minimize vibration and drift and employs precise translation stages to enable nanobeam experiments. Results of in situ x-ray characterization of the amorphous thin film deposition process for a SrTiO3/BaTiO3 multilayer illustrate implementation of this instrument.

Isotopic enrichment of silicon by high fluence 28Si− ion implantation

Spins in the `semiconductor vacuum' of silicon-28 ($^{28}$Si) are suitable qubit candidates due to their long coherence times. An isotopically purified substrate of $^{28}$Si is required to limit the decoherence pathway caused by magnetic perturbations from surrounding $^{29}$Si nuclear spins (I=1/2), present in natural Si (nat Si) at an abundance of 4.67%. We isotopically enrich surface layers of nat Si by sputtering using high fluence $^{28}$Si$^-$ implantation. Phosphorus (P) donors implanted into one such $^{28}$Si layer with ~3000 ppm $^{29}$Si, produced by implanting 30 keV $^{28}$Si$^-$ ions at a fluence of 4x10^18 cm^-2, were measured with pulsed electron spin resonance, confirming successful donor activation upon annealing. The mono-exponential decay of the Hahn echo signal indicates a depletion of $^{29}$Si. A coherence time of T2 = 285 +/- 14 us is extracted, which is longer than that obtained in nat Si for similar doping concentrations and can be increased by reducing the P concentration in future. The isotopic enrichment was improved by employing one-for-one ion sputtering using 45 keV $^{28}$Si$^-$ implantation. A fluence of 2.63x10^18 cm^-2 $^{28}$Si$^-$ ions were implanted at this energy into nat Si, resulting in an isotopically enriched surface layer ~100 nm thick; suitable for providing a sufficient volume of $^{28}$Si for donor qubits implanted into the near-surface region. We observe a depletion of $^{29}$Si to 250 ppm as measured by secondary ion mass spectrometry. The impurity content and the crystallization kinetics via solid phase epitaxy are discussed. The $^{28}$Si layer is confirmed to be a single crystal using transmission electron microscopy. This method of Si isotopic enrichment shows promise for incorporating into the fabrication process flow of Si spin qubit devices.

ФОРМИРОВАНИЕ ТОНКИХ ПЛЕНОК MG2SI НА SI (111) И ИССЛЕДОВАНИЕ ИХ МЕТОДОМ ЭОС И СХПЭЭ

The paper presents information on the results of the formation of a thin Mg2Si film on a silicon substrate by solid-phase epitaxy in an ultrahigh-vacuum chamber of the PHI model 590 device. There are a number of difficulties in the formation of magnesium silicide films due to the low condensation coefficient and high vapor pressure. Effective methods for the formation of Mg2Si are currently being sought. As a result of our experiment, a thin film was obtained, which was studied in-situ by the method of electron Auger spectroscopy and spectroscopy of characteristic energy losses by electrons. Analysis of the Auger electron spectrum showed the presence of magnesium and silicon atoms in the composition of the formed film. From the analysis of the EELS spectra, it was found that a thin film of silicide magnesium was formed.

MgO template effect for perpendicular magnetic anisotropy in (001)-textured poly-crystalline MnAlGe films

Magnetic thin films showing high perpendicular magnetic anisotropy, Ku, and low saturation magnetization, Ms, are essential for realizing a small switching current in spintronic devices utilizing the current induced magnetization switching phenomena. The Cu2Sb-type MnAlGe intermetallic compound is a material showing uniaxial magnetocrystalline anisotropy with a relatively low Ms, which is attractive for spintronic application. In this study, the layer thickness dependence of Ku was investigated in poly-crystalline MnAlGe films, and the MgO template effect is discussed to achieve perpendicularly magnetized films in a few-nanometer thickness range. Experimental results suggested that the (001)-texture for the perpendicular magnetization was promoted by the MgO(001) template through the solid-phase epitaxy growth by annealing, which is similar with that in conventionally used CoFeB|MgO layered samples. Ku of about 2 × 106 erg/cm3 was achieved in a 5 nm-thick MnAlGe film using MgO buffer and capping exhibiting a low Ms value of approximately 200 emu/cm3 at room temperature. Although the magnitude of Ku is still in a moderate range, the low Ms is a promising feature for spintronic application.

Low-Temperature Self-Aligned-Silicide-Capable Transistor Process Using Solid-Phase-Epitaxy and Lift-Off for Hybrid Substrates

Details of a large-area-compatible sub-600 °C process for the fabrication of high mobility field-effect transistors on single crystalline silicon are presented. It is shown that lift-off and solid-phase-epitaxy (SPE) can be used in conjunction with plasma enhanced chemical vapor deposition (PECVD) to create MOSFET transistors with mobilities comparable to other high-performance techniques. Furthermore, use of an amorphous silicon/silicon oxynitride (SiOxNy) sacrificial bilayer is shown to make the process capable of self-aligned silicidation. The topography of the deposition is studied using cross-sectional scanning electron microscopy (SEM). It is shown that a successful lift-off can be achieved through the proper design of the sacrificial bilayer despite the high degree of step coverage generally exhibited by PECVD films. Cross-sectional transmission electron microscopy (TEM) is used to reveal the microstructure of the epitaxy and silicidation. Current-voltage characteristics of the fabricated transistors are presented and the field effect mobility of electrons on the fabricated devices is reported. The developed process is particularly useful in applications where high mobility transistors need to be built on silicon/nonsilicon hybrid platforms that exclude high processing temperatures.

Phase Selection and Structure of Low-Defect-Density γ-Al2O3 Created by Epitaxial Crystallization of Amorphous Al2O3.

A multistep phase sequence following the crystallization of amorphous Al2O3 via solid-phase epitaxy (SPE) points to methods to create low-defect-density thin films of the metastable cubic γ-Al2O3 polymorph. An amorphous Al2O3 thin film on a (0001) α-Al2O3 sapphire substrate initially transforms upon heating to form epitaxial γ-Al2O3, followed by a transformation to monoclinic θ-Al2O3, and eventually to α-Al2O3. Epitaxial γ-Al2O3 layers with low mosaic widths in X-ray rocking curves can be formed via SPE by crystallizing the γ-Al2O3 phase from amorphous Al2O3 and avoiding the microstructural inhomogeneity arising from the spatially inhomogeneous transformation to θ-Al2O3. A complementary molecular dynamics (MD) simulation indicates that the amorphous layer and γ-Al2O3 have similar Al coordination geometry, suggesting that γ-Al2O3 forms in part because it involves the minimum rearrangement of the initially amorphous configuration. The lattice parameters of γ-Al2O3 are consistent with a structure in which the majority of the Al vacancies in the spinel structure occupy sites with tetrahedral coordination, consistent with the MD results. The formation of Al vacancies at tetrahedral spinel sites in epitaxial γ-Al2O3 can minimize the epitaxial elastic deformation of γ-Al2O3 during crystallization.

High Optical Performance of Pseudo-Single-Crystal Semiconductors Formed on Glass Using Layer-Exchanged Ge Seed Layer

Introduction The multi-junction solar cell has continued to update the highest conversion efficiency of solar cells. However, the bulk Ge substrate, has been used as a bottom cell material for multi-junction solar cells, is too expensive for consumer application. One promising approach to reducing the fabrication cost is substituting the bulk Ge substrate with a Ge thin film on an inexpensive glass substrate.We formed a large-grained (> 100 µm) Ge layer on glass by using Al-induced layer exchange (ALILE) at a low temperature of 325 °C [1]. In addition, the resistivity of ALILE-Ge is low enough (< 103 cm-3) to be used as a bottom electrode due to highly Al doping [2]. Here, we adopted the Ge layer formed by ALILE as an epitaxial seed and grow Ge and GaAs as bottom and middle gap absorbing layers, respectively. We demonstrate the highest optical performance among the polycrystalline semiconductors formed on glass without transferring. Experimental Procedure First, the 50-nm-thick Ge seed layer on the glass substrate was prepared using ALILE (Fig. 1(a)). The upper Al layer is removed with HF (1.5%) treatment for 1 min. The resulting ALILE-Ge seed layer is highly (111)-oriented and large-grained (Figs. 1(b),(c)). Then, the Ge or GaAs layers were formed on the ALILE-Ge seed layer by solid phase epitaxy (SPE) or molecular beam epitaxy (MBE), respectively. For the SPE, amorphous-Ge layers (100-500 nm thick) were deposited at room temperature and then annealed at 350 °C in a N2 ambient (Fig. 2(a)). For the MBE, the 500-nm-thick GaAs layers were grown with heating the substrate at T g = 500‒570 °C (Fig. 3(a)). Results and Discussion Figure 2(b) shows that the SPE-Ge layers appear larger minority carrier lifetime, τ eff, than ALILE-Ge. In addition, τ eff increases with the increasing thickness of SPE-Ge, w. The SPE-Ge for w = 500 nm achieves τ eff of more than 1 µs. We calculated the bulk minority carrier lifetime of SPE-Ge, τ bulk, as expressed the equation in Fig. 2(c). From the intercept of the least-squares line in Fig. 2(c), τ bulk is determined to be 5.6 µs. Figure 2(d) shows that this value is close to that of a single-crystal Ge with hole concentration in the latter half of 1017 cm-3 [3]. SIMS measurement revealed that SPE-Ge has 6 × 1017 cm-3 of Al, which is diffused from ALILE-Ge. Assuming that the Al atoms in the SPE-Ge are fully activated as acceptors, τ bulk of the SPE-Ge is mostly limited by impurity scattering.Figure 3(b) shows that the EBSD image of the GaAs sample for T g = 520 °C was very similar to that of ALILE-Ge. Figures 3(c) and 3(d) show the stacked structure of ITO/GaAs/Ge/glass as intended. The SAED pattern in Fig. 3(e) indicates that the GaAs film is epitaxially (111) oriented and single crystalline in this area (800 nm in diameter).The composition of GaAs and the FWHMs of the TO and LO mode peaks were calculated from the EDX and Raman spectra, respectively. Figure 4(a) shows that the FWHMs initially decrease with increasing T g, indicating that the higher T g improves the crystallinity of the GaAs films. Conversely, the FWHMs increase for T g > 550 °C, due to the reduction of the As atomic ratio in the GaAs. Figure 4(b) shows clear photoresponse spectra rising near a wavelength of 900 nm, which corresponds to the bandgap of GaAs. Figure 4(c) shows that internal quantum efficiency (IQE) is maximum at wavelengths of 700–800 nm for all samples. Figure 4(d) shows that the photoresponsivity and IQE initially increase with increasing T g and decrease for T g > 550 °C. This behavior is consistent with the FWHM results. We note that the photoresponsivity and IQE of the ALILE-Ge samples are comparable to those of the single-crystal GaAs which was simultaneously grown on Ge(111) substrate. This is because GaAs on ALILE-Ge is large-grained and behaves like a pseudo-single crystal. Thus, the maximum photoresponsivity (470 mA/W) and IQE (90%) were obtained at T g = 550 °C.In conclusion, we demonstrate the great potential of ALILE-Ge as an epitaxial seed for the Ge and GaAs layers. Their optical performance is highest among the polycrystalline ones formed on glass. This achievement will directly lead to the fabrication of novel high-efficiency multi-junction solar cells based on inexpensive substrates.

Suppression of Anisotropic Heat Conduction in Ion-Substituted Layered Cobalt Oxides

Layered compounds often show the anisotropic transport properties of both electron and phonon; the electrical/thermal conductivity along with the layer is high and the electrical/thermal conductivity perpendicular to the layer is low. For example, layered Na x CoO2, which is known as a promising candidate for oxide thermoelectric material [1], exhibits a rather large thermoelectric power factor along with the CoO2 layer, whereas it shows low electrical conductivity in perpendicular to the CoO2 layer. In addition, the thermal conductivity is large along with the CoO2 layer, whereas it is small in perpendicular to the CoO2 layer. Therefore, the anisotropic electron/phonon transport properties need to be suppressed to improve the thermoelectric figure of merit of Na x CoO2. Here we demonstrate that the anisotropy in thermal conductivity κ of Ax CoO2 (A = Li, Na, Ca, and Sr) can be suppressed by increasing the weight of Ax . We fabricated Ax CoO2 epitaxial films with two different crystallographic orientations with respect to the surface normal to the substrates by the Reactive Solid-Phase Epitaxy method [2,3]. We measured the electrical conductivity σ and thermopower S along with the substrate surface whereas we measured the κ in normal to the substrate surface. We extracted the κ parallel to the layers (κ p) from the comparison of two different crystallographic orientations [4]. The κ p was 3-6 times larger than that perpendicular to the layers (κ v). The κ p decreased with increasing the atomic mass of Ax though κ v was insensitive to it; anisotropy of κ was controlled by substituting heavier Ax -ions [5]. The results of this study will be of great value in understanding fundamental heat transport properties of layered structures as well as developing Ax CoO2 based thermoelectric materials. In addition, the analysis of the anisotropic thermal conductivity used in this study can be applied to other layered materials. [1] I. Terasaki et al., Phys. Rev. B 56, R12685(R) (1997).[2] H. Ohta et al., Cryst. Growth Des. 5, 25 (2005).[3] K. Sugiura, H. Ohta et al., Appl. Phys. Lett. 88, 082109 (2006).[4] K. Sugiura, H. Ohta et al., Appl. Phys. Lett. 94, 152105 (2009).[5] H.J. Cho, H. Ohta et al., Adv. Mater. Interfaces 7, 1901816 (2019). Figure 1

Dissolution suppression of self-assembled GaSb quantum dots on silicon by proper surface preparation

The temperature stability of high-density GaSb quantum dots grown on a Si(111) surface using solid-phase epitaxy is investigated during annealing at 450 °C. It is found that the bare silicon surface plays a critical role in the GaSb decomposition through the destruction of Sb–Ga bonds with the simultaneous formation of Sb–Si bonds. GaSb decomposition can be significantly suppressed if saturated monolayer coverage in the form of the Si(111)-(√3 × √3)-R30°-Sb surface reconstruction is preliminarily formed. This allows GaSb quantum dots to be embedded in the silicon matrix using molecular beam epitaxy at high temperature.

Reduction of Interface Reactions in the Low-Temperature Solid-Phase Epitaxy of ScAlMgO4 on Al2O3(0001)

Low-temperature solid-phase epitaxy is a promising route for the synthesis of thin films of ScAlMgO4, a compound with lattice spacings close to compound semiconductors for which there are no practi...

In-situ fabrication and transport properties of (111) Y2Ir2O7 epitaxial thin film

We report on the successful fabrication of (111) oriented thin films of pyrochlore iridate Y2Ir2O7 by means of solid phase epitaxy. Essentially, we developed an entirely in situ annealing protocol, which is superior to the conventional ex-situ routine that requires multi-hour annealing to stabilize the proper pyrochlore structure. The morphological quality of the films has been confirmed by x-ray diffraction, reflectivity, and reciprocal space mapping, demonstrating their high crystallinity with a pure pyrochlore phase and an expected epitaxial relation to the substrate. Strikingly, below the magnetic phase transition, the temperature dependence of resistivity shows a power-law behavior with the power exponent of ∼3/2, characteristic of a Weyl semimetal in the presence of impurities and electron–electron correlations. Below 10 K, the magneto-transport measurements reveal the emergence of a non-saturated negative magnetoresistance up to 9 T with a small “valley” around zero field. These findings are further interpreted in relation to the weak anti-localization effect and the non-collinear antiferromagnetic ordering on the Ir sublattice.

Stable and Tunable Current-Induced Phase Transition in Epitaxial Thin Films of Ca2RuO4.

Owing to the recent discovery of the current-induced metal-insulator transition and unprecedented electronic properties of the concomitant phases of calcium ruthenate Ca2RuO4, it is emerging as an important material. To further explore the properties, the growth of epitaxial thin films of Ca2RuO4 is receiving more attention, as high current densities can be applied to thin-film samples and the amount can be precisely controlled in an experimental environment. However, it is difficult to grow high-quality thin films of Ca2RuO4 due to the easy formation of the crystal defects originating from the sublimation of RuO4; therefore, the metal-insulator transition of Ca2RuO4 is typically not observed in the thin films. Herein, a stable current-induced metal-insulator transition is achieved in the high-quality thin films of Ca2RuO4 grown by solid-phase epitaxy under high growth temperatures and pressures. In the Ca2RuO4 thin films grown by ex situ annealing at >1200 °C and 1.0 atm, continuous changes in the resistance of over 2 orders of magnitude are induced by currents with a precise dependence of the resistance on the current amplitude. A hysteretic, abrupt resistive transition is also observed in the thin films from the resistance-temperature measurements conducted under constant-voltage (variable-current) conditions with controllability of the transition temperature. A clear resistive switching by the current-induced transition is demonstrated in the current-electric-field characteristics, and the switching currents and fields are shown to be very stable. These results represent a significant step toward understanding the high-current-density properties of Ca2RuO4 and the future development of Mott-electronic devices based on electricity-driven transitions.