Solid Phase Epitaxy Technique Research Articles

Berry curvature induced spontaneous and topological-like Hall effect in magnetic Weyl semimetallic Nd2Ir2O7 (111) thin films

We report a study of longitudinal resistivity, anisotropic magnetoresistance (MR), and Hall effect on epitaxial Nd2Ir2O7 (111) thin films grown by the solid phase epitaxy technique, in which spin–orbit coupling, electronic correlation, magnetic frustration, and f-d exchange interaction are present. Temperature-dependent longitudinal resistivity (ρxx) data indicate semimetallic charge transport in the low-temperature region. Field-cooled longitudinal resistivity measurements detect negligible domain-wall conductance compared to the polycrystal or single-crystal samples. Angle-dependent MR measurement shows that the magnetic structure of Ir4+ 5d moments can be finely tuned by applying a magnetic field along different crystallographic directions. MR measurements show a field-induced modification of the Nd3+ 4f spin structure from all-in-all-out/all-out-all-in (AIAO/AOAI) (4-in-0-out) to 1-in-3-out for the applied field (H) along the [111] direction, resulting in field-induced plastic deformation of the Ir4+ domain distribution. In contrast, the application of field (H) along the [001] and [011] directions could not modify any domain distribution. A large spontaneous Hall effect (SHE) signal has been observed on Nd2Ir2O7 (111) thin film with AIAO/AOAI antiferromagnetic ordering for the application of field (H) along [001], [1̄1̄0], and [111] directions. The appearance of a large spontaneous Hall signal for the applied field along [001] and [1̄1̄0] directions rules out domain switching as the origin of the Hall effect and confirms the presence of the Weyl semimetallic phase in Nd2Ir2O7 (111) thin films. In addition to SHE, a large topological-like Hall signal is also observed, possibly due to the presence of multiple Weyl nodes in the electronic band structure.

Solid phase epitaxial thickening of boron and phosphorus doped polycrystalline silicon thin films formed by aluminium induced crystallization technique on glass substrate

Aluminium induced crystallization (AIC) technique can be used to form the high-quality and large-grained polycrystalline silicon (poly-Si) thin films, which are with the thickness of ~200 nm and used as a seed layer, on silicon nitride coated glass substrate. Thanks to aluminium metal in AIC process, the natural doping of AIC thin films is p+ type (~2 × 1018 cm−3). On the other hand, recombination of carriers can be controlled by partial doping through the defects that may have advantages to improve the thin film quality by the overdoping induced passivation. In this study, boron (B) and phosphorus (P) doped AIC seed layers were thicken to ~2 μm by solid phase epitaxy (SPE) technique at 800 °C for 3 h under nitrogen flow in a tube furnace. During the crystallization annealing, exodiffusion of dopants was formed through the SPE film from the AIC seed layer. Optical microscope and electron back scattering diffraction technique (EBSD) were used to analyse the structural quality of the Si films. The poly-Si layer with an average grain size value of ~32 μm was formed by AIC + SPE technique for P doped samples while EBSD analysis gave no results for B doped samples due to the quite deterioration on the surface of the films. AIC + SPE films were analyzed in terms of structural properties by using micro-Raman Spectroscopy and X-ray diffraction systems. The results showed that the crystallinity of compressive stress formed AIC + SPE films reached up to 98.55%. Additionally, the Raman analysis pointed out that no temperature-induced stress were generated in the AIC + SPE films while compressive stress was induced by increasing the annealing duration for doped AIC film. For all samples, the preferred orientation was 〈100〉, and the crystallite size up to 44.4 nm was formed by phosphorus doping of AIC films. The doping efficiency was determined by time-of-flight secondary ion mass spectroscopy for doped samples. A graded n+n doping profile was obtained by exo-diffusion of phosphorus from the overdoped seed layer during the epitaxial thickening while boron doping of SPE film has failed with exo-diffusion of boron from AIC seed layer into SPE film. Finally, high-quality n+n type poly-Si films were fabricated on glass substrate by using AIC + SPE technique.

Novel solid-phase epitaxy for multi-component materials with extremely high vapor pressure elements: An application to KFe2As2

We propose a novel solid-phase epitaxy technique applicable to high annealing temperatures up to 1000 °C without re-vaporization of alkali metal elements with high vapor pressures. This technique is demonstrated through the successful growth of high-quality KFe2As2 epitaxial films. The key factors are employing a custom-designed alumina vessel/cover and sealing it in a stainless tube with a large amount of atmospheric KFe2As2 powder in tightly closed sample spaces. This technique can also be effective for other materials composed of elements with very high vapor pressures, such as alkali metals, and can lead to the realization of spintronics devices in the future using KFe2As2.

Epitaxial growth and electronic structure of a layered zinc pnictide semiconductor, β-BaZn2As2

BaZn2As2 is expected for a good p-type semiconductor and has two crystalline phases of an orthorhombic α phase and a higher-symmetry tetragonal β phase. Here, we report that high-quality epitaxial films of the tetragonal β-BaZn2As2 were grown on single-crystal MgO (001) substrates by a reactive solid-phase epitaxy technique. Out-of-plane and in-plane epitaxial relationships between the film and the substrate were BaZn2As2 (00l)//MgO (001) and BaZn2As2 [200]//MgO [200], respectively. The full-widths at half maximum were 0.082° for a 008 out-of-plane rocking curve and 0.342° for a 200 in-plane rocking curve. A step-and-terrace structure was observed by atomic force microscopy. The band gap of β-BaZn2As2 was evaluated to be around 0.2eV, which is much smaller than that of a family compound LaZnOAs (1.5eV). Density functional theory calculation using the Heyd–Scuseria–Ernzerhof hybrid functionals supports the small band gap.

High-Quality Single Crystalline Ge(111) Growth on Si(111) Substrates by Solid Phase Epitaxy

Heterogeneous integration of crystalline Ge layers on cleaned and H-terminated Si(111) substrates are demonstrated by employing a combination of e-beam evaporation and solid phase epitaxy techniques. High-quality single crystalline Ge(111) layers on Si(111) substrates with a smooth Ge surface and an abrupt interface between Ge and Si are obtained. An XRD rocking curve scan of the Ge(111) diffraction peak shows a FWHM of only 260 arcsec for a 50-nm-thick Ge layer annealed at 600°C with a ramp-up rate of 20°C/s and a holding time of 1 min. The AFM images exhibit that the rms surface roughness of all the crystalline Ge layers are less than 2.1 nm.

Heteroepitaxial film growth of layered compounds with the ZrCuSiAs-type and ThCr 2Si 2-type structures: From Cu-based semiconductors to Fe-based superconductors

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe 2As 2.

Very small-size and high-density β-FeSi2 nanocrystal assemblies grown on a Si(100) substrate using an embedded solid-phase epitaxy and bionanoprocess with protein ferritin

An embedded solid-phase epitaxy technique has been studied to produce very small-size and high-density β-FeSi2 nanocrystal (NC) assemblies on a Si (100) substrate. In this procedure, a bionanoprocess is utilized, with protein “ferritin” containing Fe2O3 cores, for solid-phase epitaxial β-FeSi2-NC growth (at 500–800°C) embedded in an amorphous Si thin film. X-ray diffraction and transmission electron microscopy revealed β-FeSi2 NCs of uniform diameter (6.3±0.3nm) and high density (6.2×1011dots∕cm2). By measuring the photoluminescence spectra at 7K, a photoluminescence peak of 0.91eV is obtained as an excitonic emission from the β-FeSi2 NCs.

Ca F 2 ∕ Si ∕ Ca F 2 resonant tunneling diodes grown by B surfactant-mediated epitaxy

A special solid-phase epitaxy technique utilizing the surfactant B for the growth of crystalline Si-QWs on CaF2∕Si(111) enabled us to grow CaF2∕Si∕CaF2 double-barrier diodes exhibiting resonant tunneling effects from 77K up to room temperature with peak voltages at 0.2eV, which is very close to simple resonant tunneling model predictions. The peak voltages and currents were virtually independent of temperature. No trapping or hysteresis effects were found in the I–V characteristics which exhibited 2–7 orders of magnitude larger peak current densities than previously reported CaF2∕Si∕CaF2 RTDs.

Fabrication and characterization of heteroepitaxial p-n junction diode composed of wide-gap oxide semiconductors p-ZnRh2O4/n-ZnO

A reactive solid-phase epitaxy technique was applied to fabricate all-oxide transparent p-n heterojunctions composed of p-ZnRh2O4 and n-ZnO thin layers. Polycrystalline ZnRh2O4 was deposited on a ZnO epitaxial layer at room temperature. Thermal annealing of the bilayer sample at 950 °C in air converts the polycrystalline ZnRh2O4 layer to an epitaxial single-crystalline layer. The resultant p-n heterojunctions have an abrupt interface and exhibit a distinct rectifying I–V characteristic. The threshold voltage is ∼2 V, agreeing well with the band-gap energy of ZnRh2O4. It also exhibits photovoltage with UV-light illumination, which originates mainly from the n-ZnO layer.

Growth of silicon thin films on erbium silicide by solid phase epitaxy

A study of the growth of thin (20–30 Å) silicon overlayers on erbium silicide films epitaxially grown on Si(111), using the solid phase epitaxy technique under ultrahigh vacuum conditions was made. The silicon overlayers were characterized in situ by photoemission spectroscopy and low-energy electron diffraction for each annealing temperature. The structure of the films was analyzed (ex situ) by means of high resolution transmission microscopy. The Si overlayers are found to be essentially continuous and epitaxial after annealing at 600 °C. Electron microscopy reveals that defects are present in both the silicide and in the silicon films. The stability of thin silicon films has also been investigated.

Rapid Thermal Annealing of GaAs Films on (001) Si Substrate Grown by Solid Phase Epitaxy Technique

ABSTRACTGaAs layers grown by solid phase epitaxy on (001) Si substrate were subjected to post-growth rapid thermal anneal (RTA) at 700, 800, and 900°C for 10s in a N2 atmosphere. Rutherford backscattering/channeling showed a substantial improvement in crystalline quality of GaAs epilayer after RTA at 800°C. After RTA at 900°C for 10s, stacking faults (and/or microtwins) were eliminated entirely, and the dislocation densities in both the interface region and the film interior were reduced. High-resolution transmission electron micrographs showed a significant change in misfit dislocation structure at the interface after RTA; namely, the 90° pure edge and 60° misfit dislocations were transformed to an evenly distributed array of 90° dislocations at the interface.

Present status of solid phase epitaxy of vacuum-deposited silicon

Results of recent studies of solid phase epitaxy (SPE) of amorphous Si films deposited in ultra-high vacuum are reviewed, including experimental aspects of conducting and investigation of SPE growth, SPE kinetics in intrinsic and doped Si films, application of SPE technique for growing highly-doped epitaxial layers with sharp profiles, and lateral SPE growth over oxide.

Room-temperature codeposition growth technique for pinhole reduction in epitaxial CoSi2 on Si (111)

A solid phase epitaxy technique has been developed for the growth of CoSi2 films on Si (111) with no observable pinholes (103 cm−2 detection limit). The technique utilizes room-temperature codeposition of Co and Si in stoichiometric ratio, followed by the deposition of an amorphous Si capping layer and subsequent in situ annealing at 550–600 °C. CoSi2 films grown without the Si cap are found to have pinhole densities of 107–108 cm−2 when annealed at similar temperatures. A CF4 plasma etching technique was used to increase the visibility of the pinholes in the silicide layer. This plasma technique extends the pinhole detection resolution to 103 cm−2 and is independent of the pinhole size.

Transmission electron microscopy study of the formation of epitaxial CoSi2/Si (111) by a room-temperature codeposition technique

Co and Si have been codeposited on Si (111) substrates near room temperature in a stoichiometric 1:2 ratio in a molecular beam epitaxy system. Annealing of these deposits yields high-quality single-crystal CoSi2 layers. Transmission electron microscopy has been used to examine as-deposited layers and layers annealed at 300, 500, and 600 °C. Single-crystal epitaxial grains of CoSi2 embedded in a matrix of amorphous Co/Si are observed in as-deposited samples, while the layer is predominantly single-crystal, inhomogeneously strained CoSi2 at 300 °C. At 600 °C, a homogeneously strained single-crystal layer with a high density of pinholes is observed. In contrast to other solid phase epitaxy techniques used to grow CoSi2 on Si (111), no intermediate silicide phases are observed prior to the formation of CoSi2.

Growth of high quality CoSi 2/Si - superstructures on Si (111)

Using a newly developed solid phase epitaxy technique (SPE) it is shown that ultrathin essentially pinhole-free CoSi 2 layers can be grown epitaxially on Si (111). These form the basis of a number of short period metal/semiconductor superlattices that have been grown by combining SPE-grown CoSi 2 with MBE-grown Si. Substrate temperatures for Si-MBE have to be chosen very low (≈ 350 °C) in order to avoid a roughening of the layers.

Growth of Epitaxial CoSi2/Si Multilayers

ABSTRACTEpitaxial CoSi2/Si multilayers have been grown on Si(111) substrates with up to four bilayers of suicide and Si. To our knowledge, these are the first reported epitaxial metal-semiconductor multilayer structures. The growth of these heterostructures is complicated by pinhole formation in the suicide layers and by nonuniform growth of Si over the suicide films, but these problems can be controlled through nse of proper growth techniques. CoSi2 pinhole formation has been significantly reduced by utilizing a novel solid phase epitaxy technique in which room-temperature-deposited Co/Si bilayers are annealed to 600–650δC to form the suicide layers. Islanding in the Si layers is minimized by depositing a thin (<100Å) Si layer at room temperature with subsequent high temperature growth of the remainder of the Si. Cross-sectional transmission electron microscopy studies demonstrate that these growth procedures dramatically improve the continuity and quality of the CoSi. and Si multilayers.