Solid Phase Epitaxy Method Research Articles

Control of magnetic properties of epitaxial Mn5Ge3Cxfilms induced by carbon doping

We report the effects of carbon incorporation on the structural and magnetic properties of epitaxial Mn${}_{5}$Ge${}_{3}$C${}_{x}$ films grown on Ge(111) by the solid phase epitaxy method. This variation of molecular beam epitaxy favors the diffusion process of carbon atoms. We show that up to a carbon molar concentration $x$ of \ensuremath{\sim}0.6--0.7, the atoms are incorporated in the interstitial sites of the Mn${}_{5}$Ge${}_{3}$ lattice. Such a process results in a linear increase of the Curie temperature ${T}_{C}$ of the alloy, which can reach a value as high as \ensuremath{\sim}430 K [${T}_{C}\ensuremath{\approx}460$ K at $M({T}_{C})=0$]. Above this carbon content, ${T}_{C}$ is found to decrease. Structural characterizations reveal that Mn${}_{5}$Ge${}_{3}$C${}_{x}$ films are in perfect epitaxy when $x$ \ensuremath{\le} 0.6, whereas cluster formation in the grown layers is detected above that threshold. The clusters can be attributed to manganese carbide (MnC) compounds which are formed when the carbon content exceeds the saturation value of 0.6 by consuming previously deposited carbon. Theoretical calculations accurately reproduce the main trend of ${T}_{C}$ variation as well as the cluster formation for $x$ larger than the saturation content. In addition, we also show that after post-thermal annealing, the carbon-doped Mn${}_{5}$Ge${}_{3}$C${}_{x}$ alloys remain magnetically and structurally stable up to a temperature as high as 850 \ifmmode^\circ\else\textdegree\fi{}C. The results are very promising for integrating Mn${}_{5}$Ge${}_{3}$C${}_{x}$ into ferromagnetic-semiconductor heterostructures, the ultimate goal being the realization of spintronic devices.

Structure and Chemistry across Interfaces at Nanoscale of a Ge Quantum Well Embedded within Rare Earth Oxide Layers

Structure and chemistry across the rare earth oxide-Ge interfaces of a Gd2O3-Ge-Gd2O3 heterostructure grown on p-Si (111) substrate using encapsulated solid phase epitaxy method have been studied at nanoscale using various transmission electron microscopy methods. The structure across both the interfaces was investigated using reconstructed phase and amplitude at exit plane. Chemistry across the interfaces was explored using elemental mapping, high-angle annular dark-field imaging, electron energy loss spectroscopy, and energy dispersive X-ray spectrometry. Results demonstrate the structural and chemical abruptness of both the interfaces, which is most essential to maintain the desired quantum barrier structure.

Structural characterization of GaN epilayers on silicon: Effect of buffer layers

Cross-sections of GaN/AlN/3C-SiC/Si(111) system have been studied by electron microscopy techniques. A nanometer thick buffer layer of silicon carbide on Si(111) substrate was formed using an original solid-phase epitaxy method. The subsequent layers of gallium nitride and aluminum nitride were grown by the method hydride-chloride vapor phase epitaxy. The resulting GaN layers display neither threading dislocations nor cracks on any scale. The main fraction of defects in GaN layers have the form of dislocation pileups that are localized at and oriented parallel to the GaN/AlN interface. The dislocation density in the obtained GaN layers is (1–2) × 109 cm−2, which corresponds to a minimum level reported in the available literature. The buffer AlN layer contains nanopores, which reduce the level of stresses at the GaN/AlN interface and thus almost completely inhibit the formation of threading dislocations.

Silicon overgrowth atop low-dimensional Mg2Si on Si(111): structure, optical and thermoelectrical properties

The growth of silicon cap layers atop Mg2Si nanocrystallites (NCs) and Mg2Si two-dimensional layer with structure (2/3√3×2/3√3)-R30° were studied by methods of AES, EELS, AFM, optical and Raman spectroscopy. It was established that method of solid phase epitaxy (SPE) ensures the embedding of Mg2Si NCs in polycrystalline quality silicon cap layer at temperatures not higher than 920 K. The increase of the temperature higher than 970 K results to the moving of silicide NCs toward the surface between silicon grains in cap layer, following their destruction and Mg desorption from the surface. The MBE method with temperatures 430–485 K was used to the embedding of continuous 2D Mg2Si layer with structure (2/3√3×2/3√3)-R30° in silicon top layer (9–20 nm) with monocrystalline grains. Investigations of thermoelectrical properties of grown nanoheterostructures have shown that a Seebeck coefficient (α∼130μV/K) increases in ten times as compared with undoped silicon substrate (α=10–15μV/K).

Two-dimensional fractal-like growth on semiconductors: The formation of continuous manganese monosilicide ultrathin films on Si(111)

Continuous crystalline MnSi ultrathin films with atomically flat surfaces, which are highly expected to find an application in Si-based spintronics, are grown on Si(111)-7×7 by solid phase epitaxy method. The interfacial reaction between Mn and Si and the formation processes of the films as well as their morphological variation with annealing temperature are investigated using scanning tunneling microscopy. The MnSi ultrathin films form in a two-dimensional (2D) fractal-like mode only at a Mn coverage above ∼2 ML and at an annealing temperature in the narrow range of ∼250–300 °C. Above ∼300 °C, the growth mode gradually transforms into Volmer–Weber mode and correspondingly, the continuous films transform into 2D compact islands. The films grow with a thickness unit of quadruple layer, which is consistent with the B20-type MnSi structure.

The Investigation of Crystallization of a-Si Films Deposited on Different Orientations by Solid Phase Epitaxy Process

Abstract In the experiment of this study, amorphous silicon (a-Si) films deposited by electronbeam evaporation method on (100) p+, (110) p+ and (111) p+ Si wafer substrates were crystallized at 600 °C by the solid phase epitaxy method. The times for generating the nuclei were different from one another depending on crystallized directions of the substrates, because the number of dangling bonds existing on the surface of the substrates and also the intervals of lattices are different from one another depending on the direction of crystallization. The crystallized Si film showed lots of defects. With increasing annealing time, the number of defects decreased. Also, it included more cracks. However, crystallization of the a-Si film on the (111) Si substrate was not epitaxial growth. The crystallized Si film was composed of crystal grains smaller than 1 μm.

Characterization of Fe Silicide Growth on Si(111) Surface by Weissenberg RHEED

Fe silicide growth on a Si(111) surface has been characterized by Weissenberg RHEED. The silicides were grown in the present study via two fundamental methods, reactive deposition epitaxy (RDE) and solid phase epitaxy (SPE), with various deposition amounts of Fe. The silicide species and its epitaxial orientation were determined from three-dimensional diffraction patterns obtained using Weissenberg RHEED. It was found that only α-FeSi2 islands grew by the RDE method. Both α-FeSi2 and β-FeSi2 islands grew by the SPE method. The proportion of β-FeSi2 increased with increasing Fe deposition amount, until only β-FeSi2 was finally observed. The present results could be explained by the surface or interface reaction model wherein the reaction at the Si surface and at the Fe/Si solid interface caused α-FeSi2 and β-FeSi2 growth, respectively. [DOI: 10.1380/ejssnt.2009.866]

Electron-microscopic investigation of a SiC/Si(111) structure obtained by solid phase epitaxy

First results of the electron-microscopic investigation of thin silicon carbide (SiC) layers grown on silicon using a new method of solid phase epitaxy are presented. It is shown that, at the initial stage of epitaxial growth, a transition layer is formed which consists of various SiC polytypes. This layer occurs at the interface between the substrate and a single-crystalline SiC layer possessing predominantly a 3C polytype structure. It is established that pores with dimensions ranging from a fraction of micron to several dozen nanometers are formed in a near-surface layer of the silicon substrate, which favor the growth of epitaxial, weakly strained single-crystalline SiC layers.

Structure and Magnetism of Fe Silicides Grown on Si(111) Surfaces

We have studied structures and magnetic properties for sevral iron silicides grown on Si(111) 7×7 clean surfaces by solid phase epitaxy method, that is deposition of Fe on the surfaces at room (or low) temperature and subsequent annealing. We also have summarized almost all silicide phases depending on the deposition thickness and the annealing temperature as a schematic phase diagram. We found that some phases show ferromagnetic property arising from interface structures. For the ferromagnetism of the β-FeSi2 phase even at room temperature, the existence of a ferromagnetic silicide (close to Fe3Si) interface layer was pointed out, which leads to a hetero structure of β-FeSi2/Fe-rich silicides/Si(111). For the ferromagnetic property of 2×2-Fe phase at 40 K, the large spin polarization was proposed at the Fe atoms in the B5-type interface structure between the c-FeSi(111) ultra-thin film and the Si(111) substrate. This interface ferromagnetism will extend applications of the spintronic devices.

Temperature Dependence of the Chemical Potential in NaxCoO2: Implications for the Large Thermoelectric Power

We have performed a temperature-dependent photoemission study of a Na x CoO 2 ( x ∼0.8) epitaxial thin film prepared by the reactive solid-phase epitaxy method. The chemical potential shift as a function of temperature was derived from the Co 3 d peak shift, and revealed a crossover from the degenerate Fermion state at low temperatures to the correlated hopping state of Co 3+ /Co 4+ mixed-valence at high temperatures. This suggests that the large thermoelectric power at high temperatures should be considered in the correlated hopping picture.

β-FeSi2thin film grown on a Si(111) surface with ferromagnetic interface

Thin iron silicide films were grown by solid phase epitaxy method on Si(111) surface. Silicide structure and magnetic properties at 40 K were observed with reflection high-energy electron diffraction and surface magneto-optic Kerr effect in-situ. The bcc-Fe film was grown at 40 K and transformed to polycrystals at 670 K annealing. The SMOKE revealed ferromagnetic property of the polycrystals at 40 K. After 820 K annealing, a β-FeSi2 film was formed. This sample was ferromagnetic at 40 K. We suggest a multilayer structure including a ferromagnetic interface between the β-FeSi2 film and the Si(111) substrate.

Structure analysis of thin iron-silicide film from φ-scan RHEED Patterson function

The atomic structure of thin iron silicide film, grown epitaxially on the Si(111) surface, has been analyzed by means of the three-dimensional RHEED Patterson function analysis. The iron-silicide-terminated surface with (2 × 2) periodicity has been prepared by a solid-phase epitaxy method. 2 ML of Fe were deposited on the Si(111)-(7 × 7) surface and annealed at 500°C. Three-dimensional Patterson function was calculated from series of φ-scanned RHEED intensity distributions converted to the k-space. The resulting model of γ-FeSi2 structure consists of two silicide layers faulted to each other with three relaxed Si adatoms above the H3 site.

Heteroepitaxial growth of wide gap p-type semiconductors: LnCuOCh (Lr=La, Pr and Nd; Ch=S or Se) by reactive solid-phase epitaxy

Heteroepitaxial thin films of Cu-based oxychalcogenides, LnCuOCh (Ln = La, Pr and Nd; Ch = mixture of S and Se), were fabricated and their resulting film structures were characterized. A reactive solid-phase epitaxy method successfully yielded heteroepitaxial films on MgO(001) substrates. A high-resolution electron microscopic examination of a LaCuOS film revealed a sharp film-substrate interface. Four-axes high-resolution X-ray diffraction measurements revealed that crystalline lattices in the films are fully relaxed and that the crystallographic orientation is (001)[110] LnCuOCh || (001)[110] MgO. Furthermore, systematic variations in the lattice constant by lanthanide or chalcogen ion substitutions were observed.

Fabrication of heteroepitaxial thin films of layered oxychalcogenides LnCuOCh (Ln = La–Nd; Ch = S–Te) by reactive solid-phase epitaxy

Processes and preparation conditions for growing epitaxial thin films of Cu-based, layered oxychalcogenides LnCuOCh (Ln = La, Ce, Pr or Nd; Ch = S1-xSex or Se1-yTey) are reported. Epitaxial thin films on MgO (001) substrates were prepared by a reactive solid-phase epitaxy method. Four-axes high-resolution x-ray diffraction measurements revealed that the crystallographic orientation is (001)[110] LnCuOCh || (001)[110] MgO and the internal stress of the crystalline lattices in the films are relaxed during thermal-annealing process of the reactive solid-phase epitaxy. Furthermore, except for CeCuOS, systematic variations in the lattice constant by chalcogen or lanthanide ion substitutions were observed. These results demonstrated that the reactive solid-phase epitaxy is an efficient technique for fabricating LnCuOCh epitaxial films.

Fabrication of resonant-tunneling diodes by Sb surfactant modified growth of Si films on CaF/sub 2/Si

Molecular beam epitaxy growth of Si thin films on CaF/sub 2//Si(111) substrates has been studied. A surfactant-modified solid-phase epitaxy method, where the room temperature Si deposition was followed by annealing under Sb flux, resulted in a continuous, smooth epitaxial crystalline Si film with a sharp (/spl radic/3/spl times//spl radic/3)R30/spl deg/ reconstruction and a surface roughness of 0.15-nm rms for a 2.8-nm Si thin film. This growth technique was used to fabricate CaF/sub 2//Si/CaF/sub 2/ double-barrier resonant tunneling diodes in SiO/sub 2/ windows patterned on Si(111) substrates. A negative differential resistance (NDR) peak was found at /spl sim/0.35 V at 77 K, and the current density at the NDR peak was estimated to be 3-4 orders of magnitude higher than in earlier reports.

Fabrication of MISFET exhibiting normally-off characteristics using a single-crystalline InGaO3(ZnO)5 thin film

ABSTRACTTransparent metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated using a single-crystalline thin film of an n-type transparent oxide semiconductor, a homologous compound InGaO3(ZnO)5, grown by a reactive solid phase epitaxy method. The transparent MISFET exhibited good performances with “normally-off characteristics”, “an on/off current ratio as large as 105” and “insensitivity to visible light”. Field-effect mobility was about 2 cm2(Vs)-1, which is larger than those reported previously for MISFETs fabricated in transparent oxide semiconductors. These improved performance is thought to result from the low defect density and intrinsic-level carrier concentration of the single-crystalline InGaO3(ZnO)5 film.

New growth method of solid phase epitaxy in sputtered YIG films

A new method of growing YIG films by solid phase epitaxy was attempted, for which amorphous Y-Fe-O films were sputtered on GGG [111] substrates at room temperature with a high sputtering rate, and subsequently annealed in various atmosphere at a temperature higher than 650/spl deg/C. A possibility for SPE in YIG film could be verified by a constant growth rate of YIG films during the annealing as well as by results of both /spl theta/-2/spl theta/ scanning and a very low value of /spl Delta//spl theta//sub 50/ in rocking curves.

Device parameter dependence of temperature characteristics of lateral power MOSFET formed by solid‐phase epitaxy

AbstractThe device parameter dependence of temperature characteristics is evaluated for lateral power MOSFET having buried gates in the lower channel area and having trench gate/drains, produced by the solid‐phase epitaxy method. The device parameters considered were the gate length and the n‐drift length. The temperature coefficient (change rate) of the threshold value depends on the gate length and this tendency tends to increase as the gate length increases. However, there was no dependence on the n‐drift length. In addition, the temperature coefficient of the specific on‐resistance depends on the n‐drift length, to a degree that increases as the n‐drift length increases. However, there was no dependence on the gate length. The above facts indicate that the temperature dependence of the device characteristics tends to decrease as the device size decreases. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(5): 55–61, 2001

Growth and characterization of CoSi 2 films on Si (1 0 0) substrates

In the present work, a special solid phase epitaxy method has been adapted for the preparation of CoSi 2 film. This method includes an epitaxial growth of Co films on Si (1 0 0) substrate, and in situ annealing of the Co/Si films in vacuum. It has been found that at the substrate temperature of 360°C, fcc cobalt film grows epitaxially on the Si (1 0 0) surface. The crystallographic orientation relations between fcc Co film and Si substrate determined from the electron diffraction result are: (0 0 1) Co//(0 0 1) Si, [1 0 0] Co//[1 1 0]Si. Upon annealing at temperatures range from 500 to 600°C, Co film reacts with Si substrate and transforms into CoSi 2. The CoSi 2 films prepared by this way are characterized by XTEM, XPS and AFM.

Intermixing-controlled epitaxy for Si–Ge heterostructure devices

To fabricate high quality SiGe/Si heterostructures, control of intermixing between Si and Ge is essential during crystal growth. This paper describes the recent progress of ‘intermixing-controlled epitaxy’. A combined method of MBE (molecular beam epitaxy) and SPE (solid-phase epitaxy) was developed and used to fabricate a new heterostructure (n-Si0.8Ge0.2/Si channel/Si1−xGexbuffer layer/Si substrate). Observation by TEM demonstrated that the hetero-interface obtained by SPE was atomically flat. This interface provides the ultrahigh mobility of a two-dimensional electron gas (2DEG). In addition, the influence of atomic-hydrogen irradiation during MBE on Ge dispersion in the SiGe mixed crystal is examined. Results indicate that the number of Ge–Ge pairings was decreased by hydrogen irradiation. Such a decrease deformed the local symmetry of the Si–Ge bond from tetrahedral symmetry. As a result, photoluminescence intensity was sucessfully increased.