Low-temperature Si Buffer Research Articles

Effect of High-Temperature Annealing on Epitaxially Grown Ru Silicide Thin Films

Epitaxial growth was carried out to grow Ruthenium (Ru) silicide films. Films were grown on Si (100) substrate utilizing molecular beam epitaxy (MBE) method. Firstly, the low-temperature Si buffer layer was grown at relatively low temperature of 400 °C to accommodate lattice strain and Ru silicides epilayers were grown at 750 °C. Secondly, the effect of high-temperature annealing of 1050 °C on the grown film was depicted. To investigate the surface morphology as well as microstructural characteristics atomic force microscopy (AFM), transmission electron microscopy TEM, and x-ray diffraction (XRD) measurements were employed. Only the peaks of the Ru2Si3 phase were recorded in XRD measurements. X-ray photoelectron spectroscopy (XPS) was used to reveal the chemical and electronic composition of Ru silicide films, and a detectable change in the composition ratio toward the formation of Ru2Si3 was established after annealing. Additionally, Raman spectroscopy was utilized to evaluate the characteristics modes of entity phases.

Effects of low-temperature Si buffer thickness and SiGe oxidation on sensitivity of Si1−xGex nanowire

Si1−xGex nanowire biosensors are attractive for their high sensitivity due to the large surface-to-volume ratio, high carrier mobility, and silicon compatibility. In this work, we study the effect of the thickness of the low-temperature Si (LT-Si) buffer layer on an insulator on the sensitivity of oxidized Si1−xGex nanowire samples with different Ge contents by increasing the Si buffer thickness from 20 to 60 nm. 3-Aminopropyltrimethoxysilane (APTMS) was used as a biochemical reagent. It was demonstrated that, with the proper Ge content and LT-Si buffer thickness, the sensitivity of the Si1−xGex nanowire is high and it can be further improved by Si1−xGex oxidation. This can be attributed to the reduction of the diameter to the nanometer order, which gives rise to an increased surface-to-volume ratio and further enhances the sensitivity of the biosensor.

Strain relaxation mechanism of pseudomorphic SiGe using low-temperature technology

In the light of energy balance and screw dislocation formation model,a detailed analysis is presented on strain relaxation mechanism of pseudomorphic SiGe based on the experimental result that shear modulus of low-temperature Si (LT-Si) is less than that of SiGe.The mechanism shows that strain is relaxed by dislocation formed in LT-Si buffer layer when the thickness of pseudomorphic SiGe film is smaller than the critical thickness, and dislocations prefecentially form in LT-Si layer then the thickness of the film is equal or exceeds the critical thickness,which agrees with the experimental results reported in the literature.At the same time,an experiment was carried out to grow relaxed Si0.8Ge0.2 virtual substrate using LT-Si technology.The results indicated that dislocations were resmicted to the LT-Si layer and the relaxation degree was 85.09% without threading dislocations in Si0.8Ge0.2.The experimental results proved that the strain of pseudomorphic Si0.8Ge0.2 is relaxed by dislocations formed in the LT-Si buffer layer.

Computer simulation of the vacancy defects interaction with shuffle dislocation in silicon

The interactions between the 60 ∘ shuffle dislocation and two different types of vacancy defects in silicon are separately studied via the molecular dynamics simulation method. The Stillinger–Weber potential is used to describe the atomic interactions. The results show that the dislocation slip velocity will decrease due to the interaction with the vacancy cluster (V 6). The simulation also reveals that the divacancy will be absorbed by the dislocation. Meanwhile, a climbing of the dislocation occurs during their interactions. However, the divacancy has little effect on the dislocation slip velocity. Based on the above results, the decrease in threading dislocation density in SiGe/Si heterostructures with the use of low-temperature Si buffer layer may be explained.

Observation of in-plane strain fluctuation in relaxed SiGe virtual substrate

We investigate the morphology and strain distribution of the surface crosshatch undulation on a strain-relaxed SiGe layer grown on a low-temperature Si buffer layer by atomic force microscopy and spatially-resolved UV-Raman spectroscopy. Surface crosshatch undulation resulted from misfit dislocations at the SiGe/Si interface is associated with the strain relaxation in the SiGe layer. By means of thermal annealing, strain relaxes and the inhomogeneous in-plane strain fluctuation can be eliminated.

Misfit Dislocations in SiGe/Si Heterostructures: Nucleation - Propagation - Multiplication

We present experimental data on the effect of low-temperature buffer layers on the dislocation structure formation in SiGe/Si strained-layer heterostructures under thermal annealing. Specific subjects include mechanisms of misfit dislocation nucleation, propagation and multiplication as well as the role of intrinsic point defects in these processes. Samples with lowtemperature Si (400°C) and SiGe (250°C) buffer layers were grown by MBE. In general, the processes of MD generation occur similarly in the heterostructures studied independently of the alloy composition (Ge content: 0.15, 0.30) and kind of buffer layer. Intrinsic point defects related to the low-temperature epitaxial growth influence mainly the rate of misfit dislocation nucleation.

Thermally stimulated relaxation of misfit strains in Si1−x Gex/Si(100) heterostructures with different buffer layers

The regularities of the defect formation in Si1−xGex/Si heterostructures (x = 0.15 and 0.30), consisting of a low-temperature Si buffer layer and a SiGe solid solution, during their growth and subsequent annealings at temperatures 550–650°C are investigated by the methods of optical and transmission electron microscopy and X-ray diffraction. It is shown that the misfit-strain relaxation by plastic deformation under the conditions studied occurs most intensively in heterostructures with low-temperature SiGe buffer layers. The maximum degree of misfit-strain relaxation (no higher than 45%) is observed in the heterostructures with x = 0.30 after annealing at 650°C. The results obtained are explained by the effect of the nature and concentration of dislocation-nucleation centers, existing in low-temperature buffer layers, on the characteristics of the formation of a dislocation structure in the heterostructures under consideration.

Heterostructures Ge xSi 1−x/Si(0 0 1) grown by low-temperature (300–400 °C) molecular beam epitaxy: Misfit dislocation propagation

In previous publications [ Tuppen and Gibbings, J. Appl. Phys. 68 (1990) 1526; Hull et al., J. Appl. Phys. 70 (1991) 2052; Houghton, J. Appl. Phys. 70 (1991) 2136], the glide velocity of dislocations was analyzed and estimated in GeSi/Si (0 0 1) heterostructures grown at a temperature of 550 °C. The method of growing GeSi films with the use of a low-temperature Si buffer has been developed recently and was not involved in these studies. The present work deals with a more detailed analysis of dislocation propagation velocities in GeSi films grown with the use of the low-temperature Si buffer and those grown at low-temperatures. The dislocation velocity is estimated by the measuring of the length of misfit dislocations observed in annealed films. Additionally a method for estimating the mean threading dislocation glide velocity is used, which involves the measured threading dislocation density in a particular film and degree of its plastic relaxation directly related to the number of threading dislocations and their glide velocity. It is shown that dislocation glide velocities in heterostructures grown with the use of the low-temperature Si buffer and at low-temperatures are higher than the values predicted by the classical calculations by an order of magnitude.

Strain relaxation of GeSi/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

Plastic relaxation in GexSi1−x∕Si(001) heterostructures with x=0.18–0.62, grown at temperatures of 300–600 °C with the use of a low-temperature (350 °C) Si buffer layer, is considered. It is shown that the use of low-temperature Si and low temperature of growth of GeSi films decreases the density of threading dislocations to the value of 105–106cm−2 in heterostructures with a germanium content x<¯0.3, whereas the density of the threading dislocations in heterostructures with a higher content of Ge remains at the level of ∼108cm−2 and higher. By means of transmission electron microscopy, it is shown that the origination of dislocation half-loops from the surface in the case of a high content of germanium in the film is the main reason for the high density of threading dislocations. Growing of GeSi films with a two-step change in composition is considered. The fact that the density of the threading dislocations in the first step of the film is significantly higher than that in the substrate is noted. Because of their presence, the real thickness of insertion of misfit dislocations into the second step of the film is in ten times less than for the first layer. With an allowance for this effect, almost complete plastic relaxation of the second and further heterostructure steps can be reached at low temperatures and at a smaller thickness of GeSi films. It is concluded that the main factors of low-temperature epitaxy of GeSi, which reduce the density of the threading dislocations in heterostructures are (i) a decrease in the initial threading dislocation density and (ii) an increase in the rate of expansion of dislocation loops, which facilitates plastic relaxation with a smaller number of threading dislocations.

Misfit dislocation nucleation and multiplication in fully strained SiGe/Si heterostructures under thermal annealing

An evolution of dislocation structure formed in fully strained Si 1− x Ge x /Si(0 0 1) heterostructures during thermal annealing was studied. Heterostructures with Ge content x = 0.15 and 0.30 were grown by MBE on low-temperature Si(400 °C) and SiGe(250 °C) buffer layers. The main attention was devoted to the initial stages of strain relaxation and to the role of intrinsic point defects in misfit dislocation nucleation. A mechanism is proposed for the misfit dislocation nucleation at heterogeneous sources placed within SiGe epitaxial layer.

Strained state of the layer system depending on the SiGe layer thickness by micro-Raman mapping

Micro-Raman scattering experiments, including Raman spectroscopy and microscopy, have been carried out to study the strain state of the Si 0.75Ge 0.25 films using the low-temperature Si (LT-Si) buffer layers. SiGe layers with different thickness of 1000, 3000 and 5000 Å on LT-Si were grown on Si (0 0 1) substrates by gas-source molecular beam epitaxy (MBE). The Raman-generated images have provided a direct picture of the strain state of the SiGe layer and Si substrate with SiGe thickness. The experimental results give us evidence that the change of strain state in the SiGe film and the Si substrate with the SiGe thickness is ascribed to the LT-Si buffer layer, which can effectively adjust the strain mismatch. This function is similar to compliant effect as a thin freestanding substrate.

Effects of low-temperature Si buffer layer thickness on the growth of SiGe by molecular beam epitaxy

The thickness of a low-temperature silicon (LT-Si) buffer layer has been found to affect the growth of a SiGe overlayer significantly. 300-nm-thick Si0.7Ge0.3 films were grown on 50- to 300-nm-thick LT-Si buffer layers at 450 °C by solid-source molecular beam epitaxy. The threading dislocation density was found to decrease with the thickness of the LT-Si buffer in the thickness range of 50–200 nm. The density remains at the same low level when the thickness was increased from 200 to 300 nm. A relatively dense misfit dislocation network was observed to form at the SiGe/Si interface in samples with the LT-Si buffer layer thickness exceeding 200 nm. It is suggested that the presence of more point defects in the thicker LT-Si buffer layer is more effective to block the propagation of threading dislocations.

Crosshatching on a SiGe film grown on a Si(001) substrate studied by Raman mapping and atomic force microscopy

The morphology, stress, and composition distributions of the crosshatch pattern on a SiGe film grown on a Si(001) substrate using a low-temperature Si buffer are studied by atomic force and Raman microscopies. Crosshatching is not related to composition fluctuation regardless of the stress undulation associated with strain relaxation in the SiGe film. The crosshatch morphology arises from vertical lattice relaxation induced by piled-up misfit dislocations in the Si buffer layer and substrate. A model for crosshatch formation is proposed.

Plastic relaxation of solid GeSi solutions grown by molecular-beam epitaxy on the low temperature Si(100) buffer layer

The role of a low temperature Si buffer layer (LT-Si) in the process of plastic relaxation of molecular-beam epitaxy grown GeSi/Si(001) is studied. Probable sources and mechanisms of generation of misfit dislocations (MD) are discussed. Transmission electron microscopic and x-ray diffraction techniques are used for studying 100 nm GexSi1−x films with LT-Si and those free of such a buffer layer. The MD density is found to be much lower in the former than in the latter, and the level of the film plastic relaxation is not higher than 20% in both as-grown and annealed films with LT-Si. As the thickness of the solid solution layer reaches 300-400 nm, the plastic relaxation of the films increases to almost 100%. Therefore, the determining role of the MD multiplication is supposed. We assume the double role of the LT-Si buffer layer. First, the diffusion flux of vacancies from the LT-Si layer to the GeSi/Si interface may cause erosion of the interface and, as a result, a decrease in the rate of MD generation at the early stages of epitaxy. Second, generation of intrinsic defect clusters in the LT-Si, which are potential sources of MDs, occurs in the field of mechanical stresses of the growing pseudomorphic layer. This process is thought to be the key feature of the plastic relaxation of GeSi/LT-Si/Si(100) films which promotes MD self-organization.

High-quality Ge films on Si substrates using Sb surfactant-mediated graded SiGe buffers

High-quality Ge films were grown on Si substrates by solid-source molecular beam epitaxy using SiGe graded layer and Sb surfactant-mediation technique. Transmission electron microscopy measurements show that samples grown using this method have a lower threading dislocation density than those grown by other typical methods, such as grading at high temperature (700 °C) only, grading at intermediate temperature (510 °C) only, and the use of low temperature Si buffer. A relaxed Ge film on a 4-μm-thick graded buffer was grown and shown to have a threading dislocation density of 5.4×105 cm−2 and surface roughness of 35 Å. Ge p–i–n diodes were fabricated and tested. Under a reverse bias of 1 V, the p–i–n Ge mesa photodiodes exhibit a very low dark current density of 0.15 mA/cm2.

High-quality strain-relaxed SiGe films grown with low temperature Si buffer

High-quality strain-relaxed SiGe templates with a low threading dislocation density and smooth surface are critical for device performance. In this work, SiGe films on low temperature Si buffer layers were grown by solid-source molecular beam epitaxy and characterized by atomic force microscope, double-axis x-ray diffraction, photoluminescence spectroscopy, and Raman spectroscopy. Effects of the growth temperature and the thickness of the low temperature Si buffer were studied. It was demonstrated that when using proper growth conditions for the low temperature Si buffer the Si buffer became tensily strained and gave rise to the compliant effect. The lattice mismatch between the SiGe and the Si buffer layer was reduced. A 500 nm Si0.7Ge0.3 film with a low threading dislocation density as well as smooth surface was obtained by this method.

Solid solutions GeSi grown by MBE on a low temperature Si (001) buffer layer: specific features of plastic relaxation

The role of a low temperature Si buffer layer (LT-Si) in the process of plastic relaxation of MBE grown GeSi/Si (001) is studied. Probable sources and mechanisms of a generation of misfit dislocations (MD) are discussed. Transmission electron microscopic and X-ray diffraction techniques are used for studying 100 nm Ge x Si 1− x films with LT-Si and those free of such a buffer layer. The MD density is found to be much lower in the former than in the latter and the level of the film plastic relaxation is not higher than 20% in both as-grown and annealed films with LT-Si. As the thickness of the solid solution layer reaches 400 nm, the plastic relaxation of the films increases to almost 100%. Therefore, the determining role of the MD multiplication is supposed. We assume the double role of the LT-Si buffer layer. Firstly, the diffusion flux of vacancies from the LT-Si layer to the GeSi/Si interface may cause erosion of the interface and as a result a decrease in the rate of MD generation at the early stages of epitaxy. Secondly, the generation of intrinsic defect clusters in the LT-Si, which are potential sources of MDs, occurs in the field of mechanical stresses of the growing pseudomorphic layer. This process is thought to be the key feature of plastic relaxation of GeSi/LT-Si/Si (100) films which promotes MD self-organization.

Compliant effect of low-temperature Si buffer for SiGe growth

Relaxed SiGe attracted much interest due to the applications for strained Si/SiGe high electron mobility transistor, metal-oxide-semiconductor field-effect transistor, heterojunction bipolar transistor, and other devices. High-quality relaxed SiGe templates, especially those with a low threading dislocation density and smooth surface, are critical for device performance. In this work, SiGe films on low-temperature Si buffer layers were grown by solid-source molecular-beam epitaxy and characterized by atomic force microscope, double-axis x-ray diffraction, and photoluminescence spectroscopy. It was demonstrated that, with the proper growth temperature and Si buffer thickness, the low-temperature Si buffer became tensily strained and reduced the lattice mismatch between the SiGe and the Si buffer layer. This performance is similar to that of the compliant substrate: a thin substrate that shares the mismatch strain in heteroepitaxy. Due to the smaller mismatch, misfit dislocation and threading dislocation densities were lower.

Optical study of SiGe films grown with low temperature Si buffer

ABSTRACTIn this work, SiGe films on low temperature Si buffer layers were grown by solid-source molecular beam epitaxy and characterized by atomic force microscope, photoluminescence and Raman spectroscopy. Effects of the growth temperature and the thickness of the low temperature Si buffer were studied. It was demonstrated that using proper growth conditions of the low temperature Si buffer, the Si buffer became tensily strained and gave rise to the compliant effect. High-quality SiGe films with low threading dislocation density have been obtained.

Relaxed Si0.7Ge0.3 layers grown on low-temperature Si buffers with low threading dislocation density

Si 0.7 Ge 0.3 epilayers with low threading dislocation density have been grown on Si (001) substrates by introducing a low temperature Si buffer. Such a structure can be used as the buffer for the growth of device structures. In comparison with the conventional compositionally graded buffer system, it has the advantages of having lower threading dislocation density, smaller thickness for required degree of relaxation, and smoother surface. Experimental evidence suggests that an anomalous relaxation mechanism has been involved.