Reactive Deposition Epitaxy Research Articles

Electroluminescence properties of p‐Si/β ‐FeSi2 NCs/…/n‐Si mesa diodes with embedded multilayers of β ‐FeSi2 nanocrystallites

AbstractLight‐emitting silicon diode structures with embedded β ‐FeSi2 nanocrystallites have been fabricated using solid phase epitaxy and a combination of reactive deposition and solid phase epitaxy. Electroluminescence (EL) of the structures is studied over various temperatures and current densities under forward and reverse biases. We can state that β ‐FeSi2 NCs formed by the combined RDE+SPE method results in the formation of high density of dislocations and point defects. In contrast, defect‐free structures with β ‐FeSi2 NCs formed by SPE demonstrate intense EL (η = 1.2×10‐5%) in the wavelength range 1.4–1.6 µm even at room temperature. EL intensity dependence on the number of layers with embedded β ‐FeSi2 NCs is almost linear for the heterostructures formed on Si(100) and sublinear for the heterostructures formed on Si(111) substrate. The increase of the initial Fe layer thickness leads to the electroluminescence quenching. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Technological possibilities of Si:H thin film deposition with embedded cubic Mg2Si nanoparticles

AbstractIn this paper we introduce three technological ways how to increase an absorption coefficient of hydrogenated silicon/Si:H/ thin films and diode structures on the base of Si:H. The first one is reactive deposition epitaxy (RDE), which permit to form silicide nanoparticles of different elements /Fe, Cr, Ca, Mg/ with semiconducting properties and convenient band gap. Two more simple techniques have been also tested for the creation of magnesium silicide nanoparticles (Mg2Si‐NPs): a reactive laser ablation (RLA) and the combination of Mg vacuum evaporation and Plasma‐Enhanced Chemical Vapour Deposition (PECVD). The formation of Mg2Si‐NPs, its structures and the changes of optical absorption for samples grown by three methods have been proved by the Raman and optical spectroscopies. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Self-organized trench–island structures in epitaxial cobalt silicide growth on Si(111)

Sub-monolayer Co deposition on clean Si(111)–(7×7) surfaces has been found to form nanoscale CoSi2 islands with a surrounding trench of one Si bilayer depth and mainly hexagonal shape. The trench surface structure is largely like that of the disordered ‘1×1’ phase of the Si(111)-7×7↔‘1×1’ phase transition and comprises mostly disordered Si adatoms with small ordered patches of (11×11), (9×9), c(5×√5), c(4×4) and (2×2) structures along with some Co-ring clusters. This disordered ‘1×1’ structure within the trench has formed at 600°C, the growth temperature of CoSi2 in reactive deposition epitaxy, much below the order–disorder phase transition temperature on Si(111)–(7×7). The structure around the trench remains (7×7). Electronically the trench is semiconducting. The surrounding 7×7 structure being metallic, the island–trench structure forms a lateral metal–semiconductor–metal structure.

Fabrication of highly oriented D03-Fe3Si nanocrystals by solid-state dewetting of Si ultrathin layer

In this paper, highly oriented nanocrystals of Fe3Si with a D03 structure are fabricated on SiO2 using ultrathin Si on insulator substrate. First, (001) oriented Si nanocrystals are formed on the SiO2 layer by solid state dewetting of the top Si layer. Then, Fe addition to the Si nanocrystals is performed by reactive deposition epitaxy and post-deposition annealing at 500°C. The structures of the Fe–Si nanocrystals are analyzed by cross-sectional transmission electron microscopy and nanobeam electron diffraction. We observe that Fe3Si nanocrystals with D03, B2, and A2 structures coexist on the 1-h post-annealed samples. Prolonged annealing at 500°C is effective in obtaining Fe3Si nanocrystals with a D03 single phase, thereby promoting structural ordering in the nanocrystals. We discuss the formation process of the highly oriented D03-Fe3Si nanocrystals on the basis of the atomistic structural information.

Formation of epitaxial Co1−xNixSi2 nanowires on thin-oxide-capped (001)Si

Epitaxial Co1−xNixSi2 alloy nanowires have been grown on (001)Si substrates by a combination of reactive deposition epitaxy and oxide-mediated epitaxy. The thin native oxide layer can serve as a diffusion barrier to diminish the flux of metal atoms from the top of oxide layer to Si surface and promote the growth of nanowires. The elemental distributions of Ni and Co in nanowires were determined by energy dispersive spectroscopy in a transmission electron microscope. The factors that cause the distributions of Ni and Co in nanowires were discussed.

Uniformity of epitaxial nanostructures of CoSi2 via defect control of the Si (111) surface

The morphology and the size distribution of self-organized cobalt silicide nanostructures, grown on Si (111) substrates with controlled defects, have been investigated. An initial defect structure on the Si (111) surface is produced by quenching the substrate from just below the 7×7⇌‘1×1’ (disordered) phase transition temperature. This has produced predominantly the Si (111)-(7×7) reconstructed structure along with some disordered regions and defect lines on the substrate surface. The disordered regions contain randomly placed Si adatom ring clusters or a lattice gas of ring clusters and small patches of √7×√7 R 19° structure. These substrates have been preannealed for different durations before 0.5 monolayer Co deposition on them for forming CoSi2 by reactive deposition epitaxy. With increasing duration of substrate annealing and consequent reduction of defect density and surface roughness, a change of island morphology, a transition from bimodal to monomodal size distribution and an increase of average island size have been observed. Reduction of surface defects via substrate preannealing appears to lead to the growth of homogeneous nanostructures.

Formation of large-grain-sized BaSi2 epitaxial layers grown on Si(111) by molecular beam epitaxy

BaSi2 epitaxial films were grown on Si(111) substrates by a two-step growth method including reactive deposition epitaxy (RDE) and molecular beam epitaxy (MBE). To enlarge the grain size of BaSi2, the Ba deposition rate and duration were varied from 0.25 to 1.0nm/min and from 5 to 120min during RDE, respectively. The effect of post-annealing was also investigated at 760°C for 10min. Plan-view transmission electron micrographs indicated that the grain size in the MBE-grown BaSi2 was significantly increased up to approximately 4.0μm, which is much larger than 0.2μm, reported previously.

Formation and atomic structure of self-assembled Dy silicide clusters on the Si(111)7 × 7 surface

The formation and atomic structure of self-assembled Dy silicide clusters on the Si(111)7×7 surface are studied using scanning tunneling microscopy. We used Dy coverages in the range from 0.04ML to 0.2ML, substrate temperatures from room temperature to 500°C, and two different annealing procedures, reactive deposition epitaxy and solid phase epitaxy, to investigate the growth behavior of these clusters. Depending on the preparation conditions we found the self-assembly of different cluster types. Two main types of Dy silicide clusters occurring frequently were identified: off-center clusters that form close to an edge of the half unit cell and centered clusters that appear as triangles centered within the half unit cell. Both cluster types show a strong preference for the faulted half unit cell of the 7×7 reconstruction. By carefully analyzing the STM images we were able to identify the atomic structure of the off-center Dy silicide clusters and to propose a structure model for the centered Dy silicide clusters, both consisting of six Dy atoms and three Si atoms.

Room temperature 1.5 μm light-emitting silicon diode with embedded β-FeSi2 nanocrystallites

Light-emitting silicon diode structures with embedded β-FeSi2 nanocrystallites have been fabricated using solid phase epitaxy and a combination of reactive deposition and solid phase epitaxy. Electroluminescence (EL) of the structures was studied over various temperatures and current densities under forward and reverse biases. The structures with nanocrystallites formed by the combined method exhibited EL at temperatures below 70 K only, suggesting the presence of a high concentration of defects—non-radiative centers. High-quality defect-free structures with nanocrystallites formed by solid phase epitaxy revealed intensive room temperature EL in energy range 0.76–1.08 eV at current densities as low as 1 A/cm2.

Molecular Beam Epitaxy of BaSi2 Films with Grain Size over 4 µm on Si(111)

100-nm-thick BaSi2 epitaxial films were grown on Si(111) substrates by a two-step growth method including reactive deposition epitaxy (RDE) and molecular beam epitaxy (MBE). The Ba deposition rate and duration were varied from 0.25 to 1.0 nm/min and from 5 to 120 min during RDE, respectively. Plan-view transmission electron micrographs indicated that the grain size in the MBE-grown BaSi2 was significantly dependent on the RDE growth conditions and was varied from approximately 0.2 to more than 4 µm.

Epitaxy of Orthorhombic BaSi2 with Preferential In-Plane Crystal Orientation on Si(001): Effects of Vicinal Substrate and Annealing Temperature

We attempted to grow orthorhombic BaSi2 epitaxial films having preferential in-plane crystallographic orientation on both exact and vicinal Si(001) substrates with a miscut angle of 2° toward Si[1̄10] by reactive deposition epitaxy (RDE) and subsequent molecular beam epitaxy (MBE). On the vicinal Si(001) substrate, the initial BaSi2 nuclei formed by RDE tended to grow unidirectionally with the [010] direction parallel to Si[110] when the annealing temperature of the Si substrate before the growth was increased from 830 to 1000 °C. Transmission electron microscopy showed that the grain size of the BaSi2 films grown by MBE increased up to approximately 9 µm on the vicinal Si(001) substrate when the substrate annealing temperature was 1000 °C. This is the largest grain size ever obtained for BaSi2. Even in the case of the exact Si(001) substrate, the MBE-grown BaSi2 grains preferentially grew with the [010] direction along Si[110] when the annealing temperature was 1000 °C.

Formation, optical and electrical properties of a new semiconductor phase of calcium silicide on Si(111)

The electronic structure and morphology of calcium silicide films formed by reactive deposition epitaxy at 130 oC on Mg2Si film and at 500 oC on Si(111)7x7 surface, their optical and electrical properties have been investigated. Formation of new calcium silicide phase with high Si concentration, indirect band gap (0.63eV), high conductivity at low temperatures (50-450K) has been obtained after calcium deposition at 500 oC on Si(111)7x7 surface.

Growth, structure and luminescence properties of multilayer Si/β-FeSi 2NCs/Si/…/Si nanoheterostructures

Multilayer structures (up to 15 layers) with β-FeSi 2 nanocrystallites (NCs) buried in silicon crystalline lattice were grown by successive repetition of reactive deposition epitaxy (RDE) or solid phase epitaxy (SPE) of thin iron film on Si(100) or Si(111) substrates and silicon molecular beam epitaxy (MBE) (100–200 nm). Cross-section high resolution transmission electron microscopy (HR TEM) images and ex situ optical and Raman spectroscopy data prove that NCs formed in silicon matrix have the structure and optical properties of β-FeSi 2. The growth conditions provide no dislocations in silicon lattice were found in the course of TEM analysis. Two types of NCs depth distribution were observed: (i) layered that corresponds to iron RDE and (ii) uniform that occurs in the case of iron SPE. The uniform NCs distribution points out the fact that during a growth process NCs moves up to the surface. In spite of small nanocrystallites size (5–50 nm) and their distribution in silicon cap layers the significant photoluminescence (PL) signal at 0.8 eV was observed for all grown samples.

Epitaxial samarium disilicide films on silicon (0 0 1) substrates: growth, structural and electrical properties

In this paper the effect of the growth temperature on the structural and electrical properties of samarium silicide films is investigated. The growth of the epitaxial films is performed under ultrahigh vacuum by reactive-deposition epitaxy on silicon (0 0 1) substrates. The structural properties are assessed by reflection high-energy electron diffraction and x-ray diffractometry. Random and channelling Rutherford backscattering experiments show that the films have the correct stoichiometry, i.e. Sm/Si ratio = 1 : 2, with channelling yields as low as 20% for the best samples. The electrical properties of these films are studied by Hall effect and resistivity measurements. The films have a metallic character, with a high concentration of n-type charge carriers (>1022 cm−3) and a resistivity lower than 200 µΩ cm at room temperature. The metallic character is confirmed by the experimental optical conductivity deduced from ellipsometry experiments. Finally, evidence is presented showing the potential of SmSi2/n-type Si junctions for electronic application with a Schottky barrier height of about 0.32 eV.

Microscopic study of electrical properties of CrSi2 nanocrystals in silicon

Semiconducting CrSi2 nanocrystallites (NCs) were grown by reactive deposition epitaxy of Cr onto n-type silicon and covered with a 50-nm epitaxial silicon cap. Two types of samples were investigated: in one of them, the NCs were localized near the deposition depth, and in the other they migrated near the surface. The electrical characteristics were investigated in Schottky junctions by current-voltage and capacitance-voltage measurements. Atomic force microscopy (AFM), conductive AFM and scanning probe capacitance microscopy (SCM) were applied to reveal morphology and local electrical properties. The scanning probe methods yielded specific information, and tapping-mode AFM has shown up to 13-nm-high large-area protrusions not seen in the contact-mode AFM. The electrical interaction of the vibrating scanning tip results in virtual deformation of the surface. SCM has revealed NCs deep below the surface not seen by AFM. The electrically active probe yielded significantly better spatial resolution than AFM. The conductive AFM measurements have shown that the Cr-related point defects near the surface are responsible for the leakage of the macroscopic Schottky junctions, and also that NCs near the surface are sensitive to the mechanical and electrical stress induced by the scanning probe.

Scanning tip measurement for identification of point defects

Self-assembled iron-silicide nanostructures were prepared by reactive deposition epitaxy of Fe onto silicon. Capacitance-voltage, current-voltage, and deep level transient spectroscopy (DLTS) were used to measure the electrical properties of Au/silicon Schottky junctions. Spreading resistance and scanning probe capacitance microscopy (SCM) were applied to measure local electrical properties. Using a preamplifier the sensitivity of DLTS was increased satisfactorily to measure transients of the scanning tip semiconductor junction. In the Fe-deposited area, Fe-related defects dominate the surface layer in about 0.5 μm depth. These defects deteriorated the Schottky junction characteristic. Outside the Fe-deposited area, Fe-related defect concentration was identified in a thin layer near the surface. The defect transients in this area were measured both in macroscopic Schottky junctions and by scanning tip DLTS and were detected by bias modulation frequency dependence in SCM.

Reactive deposition epitaxy growth of iron silicide nanoparticles on Si(001)

Abstract Strain-induced, self-assembled iron silicide nanostructures were grown on Si(001) substrate by reactive deposition epitaxy. The phases and structures were characterized by scanning- and transmission electron microscopy, atomic force microscopy, and by Fourier transform infrared spectroscopy. The electrical characteristics were investigated by I–V and C–V measurements and the point defects were measured by DLTS. The size and shape of the nanoislands depended on the initial Fe thickness and on the annealing. Coexistence of different iron silicide phases was detected. Electrical characteristics show large defect concentration related to Fe.

Influence of CrSi2 nanocrystals on the electrical properties of Au/Si - p/CrSi2 NCs/Si(111) - n mesa-diodes

Semiconducting CrSi2 nanocrystals (NCs) with high density (4×1010 cm−2) and narrow size distribution were grown by reactive deposition epitaxy (RDE) of 0.6 nm Cr at 550 °C on Si(111)7 × 7 substrate. Based on DRS, AFM and TEM results silicon cap epitaxy growth procedure on silicon with high density of CrSi2 NCs has been proposed. Monolithic Si(111)/ CrSi2 NCs/Si(111) structures with three layers of buried CrSi2 NCs have been successfully grown by repeating of CrSi2 NCs formation and silicon epitaxial growth. Electrical characterization of Schottky junctions formed on the grown structures has shown that the formation of point defects generated during the growth of the Si cap layer strongly depends on the cap growth conditions and on the Cr deposition rate.

Al- and Cu-doped [formula omitted] films on Si(111) substrate by molecular beam epitaxy and evaluation of depth profiles of Al and Cu atoms

The main objective of the present work is to evaluate and compare the depth profiles of Al and Cu atoms in in-situ doped BaSi2. Furthermore, it is also desired to investigate and compare the carrier concentration of Al-doped as well as Cu-doped BaSi2 films and qualify as a potential dopant-candidate for more efficient solar cells of BaSi2. During the experiment, reactive deposition epitaxy and molecular beam epitaxy were used to develop the samples. X-ray diffraction (XRD) measurements and secondary ion mass spectroscopy (SIMS), were used to determine the structure, depth profile and composition of the already grown films. The electrical properties were characterized by Hall measurement using the van der Pauw method. In case of Al-doped BaSi2 films, it was not encouraging result due to diffusion and segregation of Al in both the surface and BaSi2/Si interface regions. On the other hand, those phenomena were not observed for Cu-doped BaS2 films. Heavily Cu-doped BaSi2 showed n+ conductivity, differently from our prediction.

Migration of CrSi 2 nanocrystals through nanopipes in the silicon cap

CrSi 2 nanocrystals (NC 1 1 NC – nanocrystal. ) were grown by reactive deposition epitaxy of Cr at 550 °C. After deposition the Cr is localized in about 20–30 nm dots on the Si surface. The NCs were covered by silicon cap grown by molecular beam epitaxy at 700 °C. The redistribution of NCs in the silicon cap was investigated by transmission electron microscopy and atomic force microscopy. The NCs are partly localized at the deposition depth, and partly migrate near the surface. A new migration mechanism of the CrSi 2 NCs is observed, they are transferred from the bulk toward the surface through nanopipes formed in the silicon cap. The redistribution of CrSi 2 NCs strongly depends on Cr deposition rate and on the cap growth temperature.