Initial stages of organometallic-vapour-phase epitaxial AIGaAs grown on (001) Si

The nucleation and growth of AIGaAs on (0 0 1) Si substrates were investigated by transmission electron microscopy (TEM). It was found that the growth temperature, growth time and V/III ratio are important parameters determining the quality of the AIGaAs nucleation layers. Decreases in the growth temperature resulted in decreases in the island size and separation, while the density increased. TEM studies also revealed that the AIGaAs islands formed under low As₄ overpressures were flatter and had higher initial densities than those grown under high As₄ overpressures. The major defects present in the AIGaAs nucleation layers were microtwins (primary and multiple twins) occurring on the inclined 1 1 1 planes of AIGaAs.     

Initial stages of cobalt film growth on MgO(001) surface

The initial stages of cobalt film growth on a MgO(001) surface was studied by methods of sample surface structure imaging by reflected electrons, low-energy electron diffraction, and Auger electron spectroscopy. The measurements were performed at room temperature for cobalt layer thicknesses up to 40 Å. It is established that cobalt film growth proceeds according to the island mechanism. In the interval of cobalt film thicknesses below ∼ 10 Å, the dominating surface phase has the form of cobalt islands with an fcc structure; at greater layer thicknesses, the surface film consists predominantly of cobalt grains with an hcp structure.     

Stabilization of the NiF2 orthorhombic phase in epitaxial heterostructures on CaF2/Si(111) substrates

Epitaxial NiF2 layers have been grown for the first time on CaF₂(111)/Si(111) substrates by molecular beam epitaxy. By high-energy electron diffraction and X-ray diffractometry, it has been established that the layers crystallize in the metastable orthorhombic phase and the epitaxial relations at the NiF₂/CaF₂ heterointerface have been determined: $ (100)_{NiF_2 } ||(111)_{CaF_2 } ,[001]_{NiF_2 } ||[1\bar 10]_{CaF_2 } $ .     

Transmission electron microscope analysis of epitaxial growth processes in the sputtered β-FeSi2/Si(001) films

The crystallographic orientation relationships and the formation process of β-FeSi₂/Si(001) films were investigated by transmission electron microscopy. A film produced by sputtering pure iron onto a silicon substrate at 600 °C consists of α- and β-FeSi₂ particles. The crystallographic relationships obtained are: (112)_α‖(111)_Si and (101)_β‖(111)_Si or (110)_β‖(111)_Si. The grains of α- and β-FeSi₂ grown inside the substrate adopt the epitaxy to Si(111), irrespective of the surface orientation of the substrate. At 500 °C, on the contrary, there are few α-FeSi₂ grains and some grains of β-FeSi₂ with (100)_β‖(001)_Si [010]_β‖[110]_Si. These results demonstrate that the lower temperature and the higher Fe concentration suppress the formation of α-FeSi₂ and promote the formation of β-FeSi₂ on/below the substrate surface.     

GaN epitaxial layers prepared on nano-patterned Si(001) substrate

We report the growth of GaN epitaxial layer on Si(001) substrate with nano-patterns prepared by dry etching facility used in integrated circuit (IC) industry. It was found that the GaN epitaxial layer prepared on nano-patterned Si(001) substrate exhibits both cubic and hexagonal phases. It was also found that threading dislocation observed from GaN prepared on nano-patterned Si(001) substrate was significantly smaller than that prepared on conventional unpatterned Si(111) substrate. Furthermore, it was found that we can reduce the tensile stress in GaN epitaxial layer by about 78% using the nano-patterned Si(001) substrate.     

Flat epitaxial ferromagnetic CoFe2O4 films on buffered Si(001)

Ferromagnetic films of spinel CoFe₂O₄ have been grown epitaxially on Si(001) using CeO₂/YSZ double buffer layers. The heterostructures were built in a single process by pulsed laser deposition with real-time control by reflection high-energy electron diffraction. YSZ and CeO₂ grow cube-on-cube on Si(001) and CoFe₂O₄ grows with (111) out-of-plane orientation, presenting four in-plane crystal domains. The interface with the buffer layers is smooth and the CoFe₂O₄ surface is atomically flat, with roughness below 0.3 nm. The films are ferromagnetic with saturation magnetization around 300 emu/cm³. The properties signal that CoFe₂O₄ is a good candidate for monolithic devices based on ferromagnetic insulating spinels.     

Growth and characterization of epitaxial anatase TiO2(001) on SrTiO3-buffered Si(001) using atomic layer deposition

Epitaxial anatase titanium dioxide (TiO₂) films have been grown by atomic layer deposition (ALD) on Si(001) substrates using a strontium titanate (STO) buffer layer grown by molecular beam epitaxy (MBE) to serve as a surface template. The growth of TiO₂ was achieved using titanium isopropoxide and water as the co-reactants at a substrate temperature of 225-250 °C. To preserve the quality of the MBE-grown STO, the samples were transferred in-situ from the MBE chamber to the ALD chamber. After ALD growth, the samples were annealed in-situ at 600 °C in vacuum (10^− 7 Pa) for 1-2 h. Reflection high-energy electron diffraction was performed during the MBE growth of STO on Si(001), as well as after deposition of TiO₂ by ALD. The ALD films were shown to be highly ordered with the substrate. At least four unit cells of STO must be present to create a stable template on the Si(001) substrate for epitaxial anatase TiO₂ growth. X-ray diffraction revealed that the TiO₂ films were anatase with only the (004) reflection present at 2θ = 38.2°, indicating that the c-axis is slightly reduced from that of anatase powder (2θ = 37.9°). Anatase TiO₂ films up to 100 nm thick have been grown that remain highly ordered in the (001) direction on STO-buffered Si(001) substrates.     

Fabrication of high quality Ge virtual substrates by selective epitaxial growth in shallow trench isolated Si (001) trenches

To further boost the CMOS device performance, Ge has been successfully integrated on shallow trench isolated Si substrates for pMOSFET fabrication. However, the high threading dislocation densities (TDDs) in epitaxial Ge layers on Si cause mobility degradation and increase in junction leakage. In this work, we studied the fabrication of Ge virtual substrates with low TDDs by Ge selective growth and high temperature anneal followed by chemical mechanical polishing (CMP). With this approach, the TDDs in both submicron and wider trenches were simultaneously reduced below 1 × 10⁷ cm^− 2 for 300 nm thick Ge layers. The resulting surface root-mean-square (RMS) roughness is about 0.15 nm. This fabrication scheme provides high quality Ge virtual substrates for pMOSFET devices as well as for III-V selective epitaxial growth in nMOSFET areas. A confined dislocation network was observed at about 50 nm above the Ge/Si interface. This dislocation network was generated as a result of effective threading dislocation glide and annihilation. The separation between the confined threading dislocations was found in the order of 100 nm.     

Reflection high energy electron diffraction and X-ray studies of AlN films grown on Si(111) and Si(001) by organometallic chemical vapour deposition

The crystallinity of AlN films on silicon substrates grown by organometallic chemical vapour deposition was investigated using X-ray diffraction and reflection high energy electron diffraction (RHEED). Single-crystal films of good quality with atomically smooth surfaces can be epitaxially grown on Si(111) substrates. Epitaxial films can also be grown on Si(001) substrates. These films have previously been reported to have a fibre structure. Different RHEED patterns were observed from the films on Si(111) and Si(001). It is established that the films grown on Si(001) consist of two types of crystallite with the following orientations: [11$\text{2}$0]_AlN//[110]_Si and [11$\text{2}$0]_AlN//[1$\text{1}$0]_Si The thickness dependence of the crystallinity was also investigated. The standard deviation σ of the X-ray rocking curve for the films grown on Si(111) is less than that for the films on Si(001) and is independent of the film thickness. The σ values for the films on Si(001) decrease markedly with increasing film thickness. On the basis of these observations, the growth mechanism of AlN epitaxial films on Si(111) and Si(001) is discussed.     

Initial stages of the ion-beam assisted epitaxial GaN film growth on 6H-SiC(0001)

Ultra-thin gallium nitride (GaN) films were deposited using the ion-beam assisted molecular-beam epitaxy technique. The influence of the nitrogen ion to gallium atom flux ratio (I/A ratio) during the early stages of GaN nucleation and thin film growth directly, without a buffer layer on super-polished 6H-SiC(0001) substrates was studied. The deposition process was performed at a constant substrate temperature of 700 °C by evaporation of Ga and irradiation with hyperthermal nitrogen ions from a constricted glow-discharge ion source. The hyperthermal nitrogen ion flux was kept constant and the kinetic energy of the ions did not exceed 25 eV. The selection of different I/A ratios in the range from 0.8 to 3.2 was done by varying the Ga deposition rate between 5 × 10¹³ and 2 × 10¹⁴ at. cm^− 2 s^− 1. The crystalline surface structure during the GaN growth was monitored in situ by reflection high-energy electron diffraction. The surface topography of the films as well as the morphology of separated GaN islands on the substrate surface was examined after film growth using a scanning tunneling microscope without interruption of ultra-high vacuum. The results show, that the I/A ratio has a major impact on the properties of the resulting ultra-thin GaN films. The growth mode, the surface roughness, the degree of GaN coverage of the substrate and the polytype mixture depend notably on the I/A ratio.     

Condensation and epitaxial growth of K on W(001)

The growth of K layers on W(001) from the first adsorption phases up to the deposition of thick films has been investigated by means of a RHEED camera, in the temperature range 143 ? T ? 273 K. At first the deposited potassium atoms form a W(001)-c(2 × 2)K⁺ structure, upon which a non-ionized but polarized adstructure grows. Further condensation is characterized by a very low binding energy of 0.09 eV to the substrate layer and consequently by a low condensation coefficient. The transition layer grows out of single adsorption events without the formation of nuclei, while the epitaxial layers growing upon it are initiated by three-dimensional nucleation. For these layers, epitaxial orientations $\text{K}\text{(001)}\text{W}\text{(001)}\text{with}\text{K}\text{[001]}\text{W}\text{[010]}$ or $\text{K}\text{[001]}\text{W}\text{[100]}$ were observed.     

Surface mound formation during epitaxial growth of CrN(001)

Single crystal CrN(001) layers, 10 to 160 nm thick, were grown on MgO(001) by reactive magnetron sputtering at growth temperatures T_s = 600 and 800 °C. Insitu scanning tunneling microscopy shows that all layer surfaces exhibit mounds with atomically smooth terraces that are separated by monolayer-high step edges aligned along ( 110) directions, indicating N-rich surface islands. For T_s = 600 °C, the root mean square surface roughness σ initially increases sharply from 0.7 ± 0.2 for a thickness t = 10 nm to 2.4 ± 0.5 nm for t = 20 nm, but then remains constant at σ = 2.43 ± 0.13 nm for t = 40, 80 and 160 nm. The mounds exhibit square shapes with edges along ( 110) directions for t ≤ 40 nm, but develop dendritic shapes at t = 80 nm which revert back to squares at t = 160 nm. This is associated with a lateral mound growth that is followed by coarsening, yielding a decrease in the mound density from 5700 to 700 µm⁻² and an initial increase in the lateral coherence length ξ from 7.2 ± 0.6 to 16.3 ± 0.8 to 24 ± 3 nm for t = 10, 20, and 40 nm, respectively, followed by a drop in ξ to 22 ± 2 and 16 ± 2 nm for t = 80 and 160 nm, respectively. Growth at T_s = 800 °C results in opposite trends: σ and ξ decrease by a factor of 2, from 2.0 ± 0.4 and 20 ± 4 nm for t = 10 nm to 0.92 ± 0.07 and 10.3 ± 0.4 nm for t = 20 nm, respectively, while the mound density remains approximately constant at 900 μm⁻². This unexpected trend is associated with mounds that elongate and join along ( 100) directions, yielding long chains of interconnected square mounds for t = 40 nm. However, coalescence during continued growth to t = 160 nm reduces the mound density to 100 µm⁻² and increases σ and ξ to 2.5 ± 0.1 and 40 ± 2 nm, respectively.     

Enhanced growth of low-resistivity titanium silicides on epitaxial Si0.7Ge0.3 on (001)Si with a sacrificial amorphous Si interlayer

Enhanced growth of low-resistivity self-aligned titanium silicides on epitaxial Si_0.7Ge_0.3 with a sacrificial amorphous Si (a-Si) interlayer has been achieved. The a-Si layer with appropriate thickness was found to prevent Ge segregation, decrease the growth temperature, as well as maintain the interface flatness and morphological stability in forming low-resistivity C54-TiSi₂ on Si_0.7Ge_0.3 grown by molecular beam epitaxy. The process promises to be applicable to the fabrication of high-speed Si-Ge devices.     

MBE Si regrowth on carbon-induced Si(001)-c(4×4) reconstructions studied by RHEED

Si(001)-c(4×4) surfaces are obtained by exposing Si(001)-2×1 surfaces at 600°C to ethylene doses that determine C coverages in the submonolayer range. This reconstruction reveals a carbon enrichment of the topmost silicon layers. As the c(4×4) reflection high energy electron diffraction pattern can be maintained in spite of rather thick Si regrowth layers, we can conclude that this C derm is able to float at the surface during the Si capping. This segregation process is strongly dependent on the growth mode. As identified by RHEED intensity oscillations, a Si step flow growth is necessary to allow carbon to float in the first four silicon top-layers. An interplay is found between the kinetic growth conditions leading to this C-segregation and those of a self-organization process of C-rich clusters that we have observed in the course of Si_1−yC_y alloy growth obtained by codeposition of silicon and carbon.     

Epitaxial growth of CoSi2 on Si(001) by reactive deposition epitaxy: Island growth and coalescence

Epitaxial CoSi₂ layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi₂(001) follows the Volmer-Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t_Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi₂/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)_CoSi2||(001)_Si and [100]_CoSi2||[100]_Si. Platelet-shaped CoSi₂ islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)_CoSi2||{111}_Si) and their narrow 〈110〉 directions by {511}_CoSi2||{111}_Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}_CoSi2||(001)_Si, and {1¯1¯1}, with {1¯1¯1}_CoSi2||{11¯1}_Si, respectively. The early stages of film growth (t_Co ≤ 13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2 × 1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t_Co ≥ 13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi₂(001) layer, with a twin density of 2.8 × 10¹⁰ cm^− 2, is obtained at t_Co = 50 Å.     

Formation of epitaxial NiSi2 nanowires on Si(100) surface by atomic force microscope nanolithography

Ni nanowries were fabricated by atomic force microscope nanolithography, evaporation, lift-off and annealing processes. Epitaxial NiSi2 nanowires on a Si(100) surface along Si(110) and (100) directions were formed by the rapid thermal annealing treatment of the Ni nanowires at 400 degrees C. The silicide nanowires along the Si(110) direction had coherent type-A Si(111) and Si(100) interfaces, while those along the Si(100) direction had a type-A Si(110) interface. Silicide nanowires were agglomerated when the Ni nanowires were annealed at high temperature (> or = 500 degrees C). The mechanism of formation of a faceted nanowire was discussed based on the minimization of the total surface energy.     

A combined In situ grazing incidence small angle X-ray scattering and grazing incidence X-ray diffraction study of the growth of Ge Islands on pit-patterned Si(001) substrates

The growth of Ge islands on a pit-patterned Si(001) template is investigated in situ, combining grazing incidence diffraction, multiple wavelength anomalous diffraction, and small angle scattering. This allows monitoring in situ the detailed structural and morphological evolutions of the pits, of the wetting-layer and of the nucleated islands on the pit-patterned Si(001) substrate. It is shown that after Si regrowth, the Si substrate displays {107} and {1 1 11} facets. During the very first stages of Ge growth, the preliminary facets of the Si substrate are energetically unfavourable, and the pit facets break up into a rather complex pattern of {10n} and {11m} facets with n > 7 and m > 11. At 5 and 6 ML, intensity rods from {105} and {113}-type facets appear in the GISAXS images revealing the formation of pyramids and domes, respectively. The degree of ordering, the shape, strain and composition of the islands are characterized during the growth process to provide a detailed evolution of their structure and morphology.     

Layer-by-layer growth of thin epitaxial Fe3Si films on GaAs (001)

Molecular beam epitaxy of Fe₃Si films on GaAs (001) is studied in situ by grazing incidence X-ray diffraction. Fe₃Si grows layer-by-layer. During deposition the growth front roughens as indicated by the damping of the X-ray oscillations and corresponding atomic force micrographs. The X-ray oscillations are modified during growth at substrate temperatures of 180 °C and below.     

Sequential structural characterization of layers in the GaN/AlN/SiC/Si(111) system by X-ray diffraction upon every growth stage

X-ray diffraction and transmission electron microscopy techniques have been used to study the dynamics of variation of the structural characteristics and deformation state in SiC, AlN, and GaN epilayers sequentially grown on a Si(111) substrate. In this system, the SiC layer has been grown by solid-phase epitaxy, while the AlN and GaN layers have been deposited by chloride-hydride vapor-phase epitaxy (HVPE) using argon as a carrier gas.