Misoriented Si Research Articles

View on Si(111)−(5×2)−Au with plasmon spectroscopy

$\mathrm{Si}(111)\text{\ensuremath{-}}(5\ifmmode\times\else\texttimes\fi{}2)\text{\ensuremath{-}}\mathrm{Au}$ represents a prototype system for an adsorbate-induced spontaneous symmetry break by formation of quasi-one-dimensional atomic chains that are metallic. Surprisingly, the geometric structure of these chains is still under debate. In this paper, we show that examination of the unoccupied band structure by plasmon spectroscopy in combination with low energy electron diffraction contains sufficient information to discriminate between suggested models, favoring an optimal concentration of 6 atoms per $(5\ifmmode\times\else\texttimes\fi{}2)$ unit cell. Furthermore, we tested the stability of this structure and found that higher concentrations of Au tend to destabilize the single-domain structure on the slightly misoriented Si(111) surface, favoring formation of $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R{30}^{\ensuremath{\circ}}\text{\ensuremath{-}}\mathrm{ordered}$ islands with a local concentration of 1 ML already at a surplus of 0.08 ML. The precise role of Au atoms at concentrations exceeding 0.60 ML that seem to stabilize formation of three domains, however, must remain open.

Study of pit formation in MBE grown GaP on misoriented Si

GaP-based alloys can be grown lattice-matched to Si, making them an attractive choice for use in Si-based multijunction solar cells. This work focuses on the growth of GaP on Si with the aim to improve the surface quality of GaP. The Si wafers used in this study were of precise (001), (001) 4° offcut toward [110], and (001) 6° offcut toward [110] orientations. GaP of high crystalline quality was grown, and high-resolution x-ray diffraction and atomic force microscopy (AFM) measurements revealed the presence of pits on the surface of GaP. Similar pits were also observed on surface of Si post growth when AFM imaging was done after chemically etching the GaP layers. The use of offcut wafers demonstrated a reduction in the pit density from over 100 μm−2 to values less than 1 μm−2 in both GaP and Si.

Growth of GaP1 − x − yAsyNx on Si substrates by chemical beam epitaxy

Chemical beam epitaxy has been used to grow layers of GaP1 − xNx, GaP1 − yAsy, and nearly lattice-matched layers GaP1 − x − yAsyNx on Si substrates. To address the issue of antiphase domain generation associated with the growth of polar semiconductors on Si, misoriented Si(001) substrates have been used combined with a carefully designed GaP buffer layer growth. The reflection high-energy electron diffraction pattern exhibits a (2 × 4) surface reconstruction after GaP buffer layer and GaP(As,N) graded layer growth, indicating the good surface quality and planarity of the grown layers. Sample composition was obtained by simultaneous acquisition of Rutherford backscattering spectrometry and nuclear reaction analysis, indicating a linear dependence of N and As mole fractions on the flux of their respective precursor. GaP1 − x − yAsyNx layers grown on Si substrates have a lattice mismatch not larger than ±0.005 for N contents in the range 0.02 < x < 0.05. High-resolution X-ray diffraction reciprocal space maps demonstrate a good crystalline quality. Intense photoluminescence spectra have been measured in all GaP1 − xNx and GaP1 − x − yAsyNx layers, as it is expected for direct bandgap materials. Two wide overlapped emission peaks are observed in all the spectra, most likely related to near bandgap recombination. The position of the higher energy peak for GaP1 − xNx and GaP1 − x − yAsyNx layers has been compared to bandgap energy calculations using the band anticrossing model, showing good agreement.

Effect of Misorientation and Preliminary Etching of the Substrate on the Structural and Optical Properties of Integrated GaAs/Si(100) Heterostructures Produced by Vapor Phase Epitaxy

It is shown for the first time that the structural and optical functional characteristics of integrated GaAs/Si(100) heterostructures can be controlled by using misoriented Si(100) substrates and their preliminary etching. The growth of an epitaxial GaAs layer on a Si substrate without the formation of antiphase domains can be carried out on a substrate deviated from the (100) singular plane by an angle smaller than 4°–6° or without a transition layer of GaAs nanocolumns. Preliminary treatment of the silicon substrate by etching makes it possible to use it for the vapor-phase epitaxial growth of a single-crystal GaAs film with a considerably smaller relaxation coefficient, which has a positive effect on the structural quality of the film. These data are in good agreement with the results of IR reflectance spectroscopy and photoluminescence and ultraviolet spectroscopy. The features of the optical properties of integrated GaAs/Si(100) heterostructures in the infrared and ultraviolet spectral regions are also defined by the relaxation coefficient.

Влияние разориентации подложки и ее предварительного травления на структурные и оптические свойства интегрированных гетероструктур GaAs/Si(100), полученных методом газофазной эпитаксии

AbstractIt is shown for the first time that the structural and optical functional characteristics of integrated GaAs/Si(100) heterostructures can be controlled by using misoriented Si(100) substrates and their preliminary etching. The growth of an epitaxial GaAs layer on a Si substrate without the formation of antiphase domains can be carried out on a substrate deviated from the (100) singular plane by an angle smaller than 4°–6° or without a transition layer of GaAs nanocolumns. Preliminary treatment of the silicon substrate by etching makes it possible to use it for the vapor-phase epitaxial growth of a single-crystal GaAs film with a considerably smaller relaxation coefficient, which has a positive effect on the structural quality of the film. These data are in good agreement with the results of IR reflectance spectroscopy and photoluminescence and ultraviolet spectroscopy. The features of the optical properties of integrated GaAs/Si(100) heterostructures in the infrared and ultraviolet spectral regions are also defined by the relaxation coefficient.

Control Over Dimer Orientations on Vicinal Si(100) Surfaces in Hydrogen Ambient: Kinetics Versus Energetics

In chemical vapor ambience, Si(100) surfaces and hydrogen are strongly interacting with each other at relevant process temperatures. Energetic considerations cannot solely describe step and terrace formation sufficiently, as the formation of equilibrium surface reconstructions can be counteracted by surface kinetics. In recent years, the combination of in situ reflection anisotropy spectroscopy (RAS) and complementary UHV‐based surface sensitive techniques helped to understand and control the entire Si(100) surface preparation, in particular step and domain formation, which strongly depend on the applied process conditions and surface misorientation. Here, we discuss vicinal, 6° misoriented Si(100) surfaces in comparison to results on larger terraces in order to derive a general view on how to promote either a kinetically or an energetically driven step formation. Dictated by the dominant driving force, monohydride Si(100) surfaces with “A‐type” (1 × 2) or “B‐type” (2 × 1) majority domain can be prepared, as we confirm with RAS as well as low energy electron diffraction, scanning tunneling microscopy and Fourier‐transform infrared spectroscopy. Well‐ordered DB double layer steps at the vicinal B‐type Si(100) surface cause a step‐related, derivative‐like RAS signal, in contrast to all other surfaces. In general, we confirm that high H2 pressures promote kinetically driven processes, while the impact of energetics increases with offcut magnitude.

Impact of the substrate misorientation and its preliminary etching on the structural and optical properties of integrated GaAs/Si MOCVD heterostructures

This is the first attempt to make a report regarding the control of the structural and optical functional characteristics of integrated GaAs/Si heterostructures owing to the employment of preliminary etched misoriented Si substrates. The epitaxial GaAs layer on silicon substrates with no formation of the antiphase domains can be grown using substrates deviating less than 4°–6° from the singular (100) plane or without the use of a transition layer of GaAs nano-stakes. Preliminary etching of the Si substrate made it easier to acquire an epitaxial GaAs film in a single-crystalline state with a significantly less relaxation factor MOCVD, which positively influences on the structural performance of the film. These data agree with the results of Infrared reflection spectroscopy as well as Photoluminescence and UV-Vis spectroscopy. The optical properties of the integrated GaAs/Si (100) heterostructures in the IR and UV spectral regions were also identified by means of the relaxation coefficients.

Experimental study of structural and optical properties of integrated MOCVD GaAs/Si(001) heterostructures

This is the first report of the control of the structural and optical functional characteristics of integrated GaAs/Si(001) heterostructures due to the use of misoriented Si(001) substrates with protoporous sublayer. The growth of the epitaxial GaAs layer on silicon substrates without formation of the antiphase domains can be performed on substrates deviating less than 4°–6° from the singular (001) plane or without the use of a transition layer of GaAs nano-columns. Preliminary etching of the silicon substrate with protoporous Si sublayer formation facilitated the acquisition of an epitaxial GaAs film in a single-crystalline state with a considerably less residual strain factor using MOCVD, which has a positive effect on the structural quality of the film. These data are in a good agreement with the results of IR reflection spectroscopy as well as PL and UV spectroscopy. The optical properties of the integrated GaAs/Si (001) heterostructures in the IR and UV spectral regions were also determined by the residual strain value.

A Study on 3C-SiC Carbonization on Misoriented Si Substrates: From Research to Production Scale Reactors

In this work we have studied the carbonization of 3C-SiC on misoriented Si substrates, using different thermal ramp rates and shapes. We observed that the heating rate (°C/sec) from carbonization temperature to film growth temperature plays a major role in controlling the void density. Moreover, void formation can be eliminated by the introduction of silane at different temperatures during the heating ramp. The studies were performed on a small research reactor and the results were successfully transferred to a production scale reactor, aimed to the production of 3C-SiC power devices manufactured on 100 and 150 mm Si substrates.

Semipolar AlN on Si(100): Technology and properties

Initial stages of the semipolar AlN layer formation by chloride-hydride vapor phase epitaxy on a misoriented Si(100) substrate with a thin intermediate nano-SiC layer grown by atomic substitution method are investigated. It is found that once the growth rate of AlN layer on a nano-SiC/Si(100) substrate is about 0.02μm/h, the layer is formed in a polar direction. On the other hand, at the growth rate of 1μm/h the layer is formed in a semipolar direction. We propose the model of the semipolar AlN layer growth based on the formation of the special structure on the SiC layer synthesized by atomic substitution and on the possibility of the matching of the quasi-lattices of Al(20−23) and 3CSiC(100) planes assuming bonding of four atoms from the layer to four atoms of the 3CSiC quasi-lattice consisting of three lattice unit cells in one of the directions.

The structural state of epitaxial GaP films of different polarities grown on misoriented Si(001) substrates

The structure of GaP films grown by molecular-beam epitaxy on vicinal Si(1113) substrates has been studied by X-ray diffraction. It is established that the crystalline lattice of a pseudomorphic film rotates about the axis toward increasing deviation from the singular orientation, while the subsequent relaxation leads to rotation in the opposite direction. This is valid for the films of both (001) and (001) polarities. Differences between the surface morphologies of relaxed and pseudomorphic GaP films are revealed.

MOCVD growth and characterization of multi-stacked InAs/GaAs quantum dots on misoriented Si(100) emitting near 1.3 μm

We report near 1.3μm strong photoluminescence (PL) emission from 5-stacked InAs/GaAs quantum dots (QDs) monolithically grown on Si (1 0 0) substrates with 4° miscut towards [110] direction by metal organic chemical vapor deposition (MOCVD). The metamorphic QD samples on Si were grown by three-step method, in which bottom Al0.8Ga0.2As cladding and GaAs waveguide layers were simultaneously incorporated in order to fabricate Si-based QD light emitting devices later. In particular, the GaAs waveguide layer grown with low and high temperature alternated significantly suppresses the upwards propagating of threading dislocations (TDs) into QD region and flattens the surface for latter adjacent nucleation of QDs. As a result, room-temperature photoluminescence intensity of as-grown Si-based InAs/GaAs QD sample attains 87% of that on GaAs and its PL peak as long as 1280nm with the full width at half maximum value up to 78nm (i.e., 60meV). Our study shows the great opportunity of using MOCVD grown Si-based metamorphic QDs for 1.3μm band light emitting devices.

3C-SiC carbonization optimization and void reduction on misoriented Si substrates: from a research reactor to a production scale reactor

In this work, we studied how to optimize the carbonization process in order to deposit cubic SiC (3C-SiC) on misoriented Si substrates. The carbonization process is a key step to obtain device-quality layers and to partially release the strain due to the lattice mismatch between the substrate and the thin 3C-SiC film. One of the common problems in SiC/Si epitaxy is the presence of interfacial voids that can degrade the structural quality of the deposited film and the electrical properties in vertical devices. Carbonization optimization requires careful control of several parameters, in particular temperature, precursor flows, and heating ramps. Precise tailoring of this process on a production reactor with the understanding of all the involved variables would require huge effort in terms of time and money, so it is desirable to perform part of this work on a smaller scale research reactor, which is more versatile and economically viable. Starting from a baseline process for 3C-SiC power devices on 100 mm Si already developed on a production reactor, we used a small research reactor to investigate how the thermal heating profile during the carbonization ramp influences the void density on the Si substrate. We have also studied how the introduction of silane during the carbonization ramp can effectively suppress void formation. After having obtained a comprehensive understanding of the variables involved in the process, the key ideas were successfully implemented in the production reactor, resulting in a significant reduction of interfacial voids.

Determination of hardness and Young's modulus for important III–V compound semiconductors

Nanoindentation was used to determine material hardness and Young's modulus in a wide compositional range of GaAsxP1−x, Ga1−xInxP, Ga1−xInxAs and Al0.5Ga1−xInxAs compound semiconductors. Ternary and quaternary samples were grown on misoriented GaAs(001) and Si(001) substrates by metallorganic vapor phase epitaxy. Nanoindentation measurements were made using a Berkovich shaped indenter in a continuous stiffness mode. This method allows a continuous measurement of modulus and hardness over the complete indentation depth. Parabolic and linear trends were found for the Young's modulus of the investigated compound semiconductors. In case of hardness, parabolic trends associated with solid solution strengthening were found for all investigated material systems.

Breaking Elastic Field Symmetry with Substrate Vicinality

We present a novel approach to engineer the growth of strained epitaxial films based on tailoring the elastic-interaction potential between nanostructures with substrate vicinality. By modeling the island-island interaction energy surface within continuum elasticity theory, we find that its fourfold symmetry is broken at high miscuts, producing directions of reduced elastic-interaction energy. As a consequence, it is possible to direct the Ge island growth on highly misoriented Si(001) substrates towards desired pathways.

Atomic surface structure of Si(1 0 0) substrates prepared in a chemical vapor environment

Subsequent III–V integration by metal-organic vapor phase epitaxy (MOVPE) or chemical vapor deposition (CVD) necessitates elaborate preparation of Si(100) substrates in chemical vapor environments characterized by the presence of hydrogen used as process gas and of various precursor molecules. The atomic structure of Si(100) surfaces prepared in a MOVPE reactor was investigated by low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) available through a dedicated, contamination-free sample transfer to ultra high vacuum (UHV). Since the substrate misorientation has a fundamental impact on the atomic surface structure, we selected a representative set consisting of Si(100) with 0.1°, 2° and 6° off-cut in [011] direction for our study. Similar to standard UHV preparation, the LEED and STM results of the CVD-prepared Si(100) surfaces indicated two-domain (2×1)/(1×2) reconstructions for lower misorientations implying a predominance of single-layer steps undesirable for subsequent III–V layers. However, double-layer steps developed on 6° misoriented Si(100) substrates, but STM also showed odd-numbered step heights and LEED confirmed the presence of minority surface reconstruction domains. Strongly depending on misorientation, the STM images revealed complex step structures correlated to the relative dimer orientation on the terraces.

Formation of edge misfit dislocations in GexSi1−x(x∼0.4–0.8) films grown on misoriented (001)→(111) Si substrates: Features before and after film annealing

The dislocation structure at the initial stage of relaxation of GexSi1−x films (x∼0.4–0.8) grown on Si(001) substrates tilted at 6° to the nearest (111) plane is studied. One of the directions along which edge dislocations are formed is no longer in the plane of the interface but crosses the latter at the angle of miscut. Therefore, long edge misfit dislocations (MDs) cannot exist in the direction of substrate misorientation, because their ends move away from the interface during dislocation propagation. Two different mechanisms of formation of short segments of edge (90°) MDs in the direction of substrate misorientation are found. The first mechanism is the correlated nucleation of complementary 60° dislocation half-loops manifested in the form of the so-called Y-center consisting of a short segment of the 90° MD and 60° MDs diverging from this segment in form of two rays in the miscut direction. In the second mechanism, the 90° MD segment is formed owing to intersection of already existing complementary 60° MDs slipping in mirrorlike inclined planes {111}. Samples annealed at higher temperatures contain MD segments, which lose their contrast on one of the TEM images taken to detect edge dislocation segments in the two-wave diffraction mode but do not coincide with the direction [110] (they pass along the intersections of the mirrorlike inclined planes {111} with the surface of the misoriented Si substrate). To explain this phenomenon, a model is proposed, where one of the pair of complementary 60° MDs propagating at an angle to each other continuously approaches the other by the cross-slip mechanism. Formation of a chain of edge MD segments connected by a pair of 60° MDs becomes possible. The averaged direction of such a dislocation structure coincides with the direction of one of the 60° MDs.

Lattice relaxation process and crystallographic tilt in GaP layers grown on misoriented Si(001) substrates by metalorganic vapor phase epitaxy

A lattice relaxation process and a crystallographic tilt in GaP layers grown on misoriented Si(001) substrates by metalorganic vapor phase epitaxy were investigated. Strained pseudomorphic GaP layers without defects on Si were successfully achieved by the optimization of growth conditions. Below critical thickness, the strained GaP layers were tilted in the misoriented direction of the Si substrates and triclinically distorted. Above critical thickness, the residual strain in the GaP layers was progressively relaxed with increased thickness of the GaP layers by forming 60° misfit dislocations propagating to the two orthogonal ⟨110⟩ directions at the heterointerface. X-ray diffuse scattering around the symmetrical GaP(004) diffraction was observed after introducing misfit dislocations. Diffuse scattering became dominant with an increase in the density of the misfit dislocations and resulted in a broadening of the full width at half maximum of the x-ray rocking curves. The GaP layers that were relaxed with highly dense misfit dislocations were tilted opposite of the misoriented direction due to the imbalance nucleation of the misfit dislocations on each {111} glide plane.

High-Temperature Growth of GaP on Si Substrates by Metalorganic Vapor Phase Epitaxy

GaP was grown on misoriented Si substrates using metalorganic vapor phase epitaxy (MOVPE). At 700 and 800 °C, no mirror surface was obtained. A mirror surface was achieved at 830 °C with a high PH3 flow rate. The island nucleation density at the initial growth stage increased with temperature between 700 and 800 °C and saturated beyond 800 °C. Islands with a density of 1011 cm-2 nucleated at 830 °C. Cross-sectional transmission electron microscopy (c-TEM) shows that a 5-nm-thick GaP layer was formed by coalescence of the islands at 830 °C. A cross-hatched pattern (CHP) was observed for a 200-nm-thick GaP layer grown at 830 °C. The CHP indicates that the quality of the GaP layer was high. Cross-sectional TEM reveals that few stacking faults and dislocations exist in 5- and 40-nm-thick GaP layers on Si substrates.

High-speed GaAs metal gate semiconductor field effect transistor structure grown on a composite Ge∕GexSi1−x∕Si substrate

In this study we used a low-pressure metal organic vapor phase epitaxy method to investigate the growth of GaAs metal gate semiconductor field effect transistor (MESFET) structures on a Si substrate. The buffer layer between the Si substrate and the grown GaAs epitaxial layers was a composite Ge∕Si0.05Ge0.95∕Si0.1Ge0.9 metamorphic layer. We used transmission electron microscopy to observe the microstructures formed in the grown GaAs∕Ge∕SixGe1−x∕Si material and atomic force microscopy to analyze the surface morphology and the formation of antiphase domains in the GaAs epitaxial layers. The measured Hall electron mobility in the channel layer of a MESFET structure grown on a 6° misoriented Si substrate was 2015 cm2 V−1 s−1 with a carrier concentration of 5.0×1017 cm−3. The MESFET device fabricated on this sample exhibited good current-voltage characteristics.