Substrate Misorientation Research Articles

The Growth of InAsxSb1 –x Solid Solutions on Misoriented GaAs(001) Substrates by Molecular-Beam Epitaxy

The effect of a substrate misorientation degree from a singular face on the composition and morphology of layers of InAsxSb1 –x solid solutions obtained by molecular-beam epitaxy on a GaAs surface has been investigated. The substrates of GaAs wafers with the orientation (100) misoriented in the direction [110] by 0°, 1°, 2°, and 5° are used. The heterostructures are grown at temperatures of 310°C and 380°C (respectively, the lower and upper boundaries of the temperature range in which structurally perfect InAsxSb1 –x films form). The effect of the molecular form of arsenic (As2 or As4) on the composition of the layers is studied. The composition and structural properties are investigated using high-resolution X-ray diffractometry (HRXRD) and atomic-force microscopy (AFM). It is established that, in the series of misorientation angles 0° → 5°, the arsenic fraction x increases consecutively when using fluxes of both As2 and As4 molecules. With the As2 molecular flux, the fraction x increases only a little (1.05 times) with increasing degree of misorientation, while, when using the As4 flux, the increase in x is 1.75 times. An increase in the growth temperature leads to growth in the arsenic fraction in the solid solution. The surface morphology improves with an increasing degree of misorientation at a low growth temperature and degrades at a high temperature.

Effect of GaAs(100) substrate misorientation on structural, electronic, and optical properties of AlN nano-sized films obtained by reactive plasma-ion deposition

With the use of reactive plasma-ion deposition, thin nano-sized films of AlN were obtained on the substrates of GaAs(100) with a different degree of misorientation relative to the <100> direction.It was shown that the growth of the AlN films on GaAs substrates with a small degree of misorientation resulted in the formation of the AlN films in the nano-crystalline state. Hence, the film with a cubic crystal system was formed on a precisely oriented GaAs substrate, while on the substrate with 2° misorientation, the film consisted of a mixture of the AlN phases with cubic and hexagonal crystal symmetry. At the same time, the growth of the films on the substrates with a high degree of misorientation resulted in the disappearance of the long-range order in the crystalline structure of the AlN films; this implied the formation of the AlN phase in the amorphous state. The misorientation of the GaAs(100) substrate affected the sizes of the nano-islands formed on the surface of the AlN film. The lower the misorientation of the GaAs(100) substrate, the smaller were the lateral sizes of the nano-islands.Comparing our data for the optical band gap and the dispersion of the refractive index obtained by reactive ion-plasma deposition and the results for the AlN films grown by reactive sputtering, which is the closest method to the technology used in our work, we found that depending on the conditions of the reactive sputtering, nano-sized films of AlN with refractive index values within the range of 2.26–2.38 for the energy range of ∼4.7–4.9 eV and optical band gaps within 5.34–5.71 eV, were obtained. It was possible to obtain thin films with refractive index values within the range of 1.65–3.35 for energy values of ∼4.7–4.9 eV and optical band gaps of ∼5–6.2 eV by the application of the AlN deposition on the surface of semiconductor materials proposed in this study.An increase in the misorientation degree for the GaAs substrate was observed along with an improvement in the structural quality of nano-sized AlN films as well as in their electron structure, surface morphology, and optical properties. Thus, the morphology, surface composition, and optical functional characteristics of hetero-phase AlN/GaAs systems can be controlled by using GaAs substrates with a specified degree of misorientation relative to the <100> direction.

Effect of substrate misorientation on the concentration of impurities and surface morphology of an epitaxial GaN layer on N-polar GaN substrate by MOVPE

This study examines the effect of (0 0 0 −1) GaN substrate misorientation on the residual impurities and surface morphology of N-polar GaN grown by metalorganic vapor-phase epitaxy. Carbon, silicon, and oxygen concentrations decreased with increasing GaN substrate misorientation angle, with the lowest impurity concentration achieved for a misorientation angle of 2° toward the m-axis, with 6 × 1015 cm−3 carbon, 6 × 1015 cm−3 silicon, and 4 × 1017 cm−3 oxygen atoms. The oxygen concentration was measured at a depth of 0.5 μm below the wafer surface, and the oxygen concentration decreased with increasing thickness. The incorporation of carbon and oxygen revealed a strong dependence on the misorientation angle. The step distance height of the steps parallel to the [1 1 −2 0] direction (or perpendicular to the [1 −1 0 0] m-direction) was confirmed to be a double-height layer step. This phenomenon indicated that m-direction steps are stable for N-polar growth in GaN. In cases of large misorientation toward the m-axis in of the GaN substrate it was difficult to control the misorientation perpendicular to the nominal direction leading to a-axis direction by wafer bowing at wafer manufacturing. Therefore, step-bunching was generated for each symmetric m-axis due to an increase in the compound's off-angle, thus causing the surface roughness to become large.

Рост твердых растворов InAs-=SUB=-x-=/SUB=-Sb-=SUB=-1-x-=/SUB=- на отклоненных подложках GaAs(001) методом молекулярно-лучевой эпитаксии

The influence of substrate misorientation degree on the composition and morphology of layers during molecular-beam epitaxy of InAsxSb1−x solid solutions on the GaAs surface was studied. The GaAs wafers with orientation (001), which were miscuted in the [110] direction by 0, 1, 2 and 5◦, were used as substrates. The growth of heterostructures was performed for temperatures of 310◦C and 380◦C (lower and upper boundaries for the temperature range of structurally perfect InAsx Sb1−x films formation, respectively). The influence of the arsenic molecular form (As2 or As4) on the composition of layers was studied. Studies of composition and structural properties were carried out using high-resolution X-ray diffractometry (HRXRD) and atomic force microscopy (AFM). It was established that in the series of misorientation from 0 to 5◦ the arsenic fraction x increases consecutively with the use of both flux of As2 and flux of As4 molecules. When the flux of As2 molecules is used, the fraction x increases insignificantly (in 1.05 times) with a rise of misorientation degree, but when using As4 molecules, x increases in 1.75 times. The increase of the growth temperature leads to the rise of the arsenic fraction in the solid solution. The morphology of the surface improves during increasing of misorientation degree at a low growth temperature and degrades at high temperatures.

Crack-free GaN-based ultraviolet multiple quantum wells structures grown on AlN/2° misoriented sapphire template

An approach of growing crack-free GaN-based InGaN-multiple quantum wells (MQWs) with emission at 365 nm on AlN template, instead of conventional GaN template, by metal-organic chemical vapor deposition is presented. The AlN template used here was grown on the vicinal 2° misoriented sapphire substrate. Scanning electron microscopy and atomic force microscopy investigation show that cracks do not form in the MQWs structure grown on an AlN template. The full width at half maximum of high resolution X-ray diffraction rocking curve of the n-Al0.02Ga0.98N buffer decreases dramatically when grown on an AlN template, indicating improved crystalline quality. Moreover, Photoluminescence spectra show that the employment of AlN/2° misoriented sapphire template is beneficial to internal quantum efficiency and its thermal stability. Finally, transmission election microscopy reveals a prominent reduction of dislocation density at the undoped GaN/AlN interface.

The influence of the substrate misorientation on the structural quality of GaN layers grown by HVPE

The paper describes a Transmission Electron Microscopy study on the structural quality of GaN samples grown by Hydride Vapor Phase Epitaxy (HVPE) on ammonothermal (Am) GaN seeds. The only difference between these samples is the crystallographic direction of misorientation of the Am GaN seeds for the further growth. The studied samples were 1° misoriented in two perpendicular crystallographic directions: the [1100] and the [1120]. Cross-section samples were studied and showed that growth of homo-epitaxial GaN on the substrate tilted toward the [1100] direction appeared to lead to lower defect density than those tilted toward the [1120] direction. This was associated with slow growth on {1011} planes that are oriented “edge-on” for the growth along [1120] direction leading to the formation of facets while the [1100] direction is devoid of such facets. The competition between slow and fast growth rates on particular planes would lead to the change of the crystal shape such as triangle or trapezoidal one. Our present study also found that cracks in the samples tilted toward the [1120] direction are formed and they are the origin for half loops. Moreover, dislocation propagation from these cracks is observed. Such cracks were not observed for the samples tilted toward the [1100] directions, probably due to more uniform growth. There were no dislocations at the sample surface. However, some parasitic growth occurred on the wafer edges for both samples. Cross-section microscopy found high dislocation density in these areas with and a majority of them are edge dislocations.

GaN microrod sidewall epitaxial lateral overgrowth on a close-packed microrod template

We demonstrate a GaN growth method using microrod sidewall epitaxial lateral overgrowth (MSELO) on a close-packed microrod template by a nonlithographic technique. The density and distribution of threading dislocations were determined by the density and distribution of microrods and the nucleation model. MSELO exhibited two different nucleation models determined by the direction and degree of substrate misorientation and the sidewall curvature: one-sidewall and three-sidewall nucleation, predicting the dislocation density values. As a result, the threading dislocation density was markedly decreased from 2 × 109 to 5 × 107 cm−2 with a small coalescence thickness of ∼2 µm for the close-packed 3000 nm microrod sample.

Influence of Substrate Misorientation on the Composition and the Structural and Photoluminescence Properties of Epitaxial Layers Grown on GaAs(100)

The influence of the degree of misorientation and treatment of a GaAs substrate on the structural and optical characteristics of homoepitaxial GaAs/GaAs(100) structures grown by metal–organic chemicalvapor deposition is studied. From the data obtained by a series of structural and spectroscopic techniques, it is shown that the degree of deviation of the substrate from the exact orientation towards the [110] direction by an angle of up to 4° brings about stepwise growth of the GaAs film in the initial stage and a further increase in the degree of misorienration towards the [110] direction to 10° results in an increase in the number of structural defects in the epitaxial film. At the same time, the samples of homoepitaxial structures grown by metal–organic chemical-vapor deposition on GaAs(100) substrates misoriented by 4° towards the [110] direction possess the highest photoluminescence efficiency; it is ~15% higher than the corresponding quantity for structures grown on precisely oriented GaAs(100) substrates. Preliminary polishing of the GaAs substrate (removal of an oxide layer) also yields the intensification of photoluminescence emission compared to emission in the case of an unpolished substrate of the same type. For samples grown on substrates misoriented by 4°, such an increase in the photoluminescence efficiency is ~30%.

Влияние разориентации подложки на состав, структурные и фотолюминесцентные свойства эпитаксиальных слоев, выращенных на GaAs(100)

AbstractThe influence of the degree of misorientation and treatment of a GaAs substrate on the structural and optical characteristics of homoepitaxial GaAs/GaAs(100) structures grown by metal–organic chemicalvapor deposition is studied. From the data obtained by a series of structural and spectroscopic techniques, it is shown that the degree of deviation of the substrate from the exact orientation towards the [110] direction by an angle of up to 4° brings about stepwise growth of the GaAs film in the initial stage and a further increase in the degree of misorienration towards the [110] direction to 10° results in an increase in the number of structural defects in the epitaxial film. At the same time, the samples of homoepitaxial structures grown by metal–organic chemical-vapor deposition on GaAs(100) substrates misoriented by 4° towards the [110] direction possess the highest photoluminescence efficiency; it is ~15% higher than the corresponding quantity for structures grown on precisely oriented GaAs(100) substrates. Preliminary polishing of the GaAs substrate (removal of an oxide layer) also yields the intensification of photoluminescence emission compared to emission in the case of an unpolished substrate of the same type. For samples grown on substrates misoriented by 4°, such an increase in the photoluminescence efficiency is ~30%.

Effects of 4° misoriented sapphire substrate on optical property of green InGaN/GaN multiple quantum wells

The effects of 4° misoriented sapphire substrate on optical property of green InGaN/GaN multiple quantum wells (MQWs) grown on planar c-plane sapphire and vicinal cut sapphire substrates were investigated. About an order of magnitude higher photoluminescent intensity of MQWs on vicinal substrate was observed compared to that of MQWs on planar substrate. Atomic force microscope and scanning electron microscope found there was a large number of V-shape pits on the structure grown on vicinal substrate. Result of Raman demonstrated that there was more stress in MQWs structure on planar substrate. It was identified by high-resolution X-ray diffraction and transmission electron microscope that the structure on vicinal substrate had higher crystalline quality. V-shape MQWs grown on semipolar sidewalls of V-shape pits on vicinal substrate played an important role in improving luminescent intensity.

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.

InGaAs/GaAs hybrid quantum well-dot nanostructures: Impact of substrate orientation and recombination mechanisms

We study the impact of substrate orientation on growth of quantum well-dots (QWD) hybrid low dimensional structures that are intermediate in properties between quantum wells and quantum dots. QWD are formed by thickness and composition modulations of InGaAs quantum well, which localize electrons and holes. We show that in case of growth on 6 degree misoriented substrates such modulations are much more pronounced than in case of growth on exact oriented substrate. The modulations result in efficient strain relaxation, which allows vertical stacking of at least fifteen 8 ML-thick In0.4Ga0.6As QWD layers without dislocation formation. Fitting of experimental dependencies of integrated PL intensity on excitation power by using ABC model allowed us determining relative contribution of different recombination processes.

Structural and optical studies of thin films of aluminum nitride grown via ion-plasma sputtering on gallium arsenide substrates with different orientations

IR and UV spectroscopy is used to study the properties of nanostructured aluminum nitride films obtained via reactive ion-plasma sputtering on GaAs substrates with different orientations. Nanostructured thin (100–200 nm) films of cubic aluminum nitride with optical bandgaps of ~5 eV and refractive indices varying from 1.6 to 4.0 in the wavelength range of ~250 nm are fabricated. Growth on a misoriented GaAs(100) substrate (4° with respect to the [110] plane) makes it possible to synthesize AlN films with smaller grains and higher refractive indices (n ~ 4). It is shown that misoriented GaAs substrates allow us to control the morphology, surface composition, and optical functional characteristics of AlN/GaAs heterophase systems.

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.

Formation of singular (001) terraces on the surface of single-crystal HPHT diamond substrates

Methods of the experimental diagnostics and control of the misorientation angle for single-crystal HPHT (High Pressure High Temperature) diamond substrates are discussed. Such substrates are used for the homoepitaxial growth of doped and undoped CVD diamond layers. The formation of singular (001) terraces on the surface of HPHT diamond after microwave-discharge-plasma etching in pure hydrogen or a hydrogen–oxygen mixture is observed. This phenomenon can be used for rapid determination of the substrate misorientation and to improve the control precision of the deviation angle during substrate polishing, or for obtaining large singular (001) areas of single-crystal diamond substrates.

Ga–In intermixing, intrinsic doping, and Wigner localization in the emission spectra of self-organized InP/GaInP quantum dots

We present study of structural and optical properties of InP/GaInP quantum (QDs) providing a weak quantum confinement and creating a platform to study Wigner localization (WL) effects using high spatial resolution optical spectroscopy. Self-organized QD structures were grown using metal-organic chemical phase epitaxy by using different substrate misorientations and cap layer deposition temperatures. Using transmission electron microscopy and energy dispersive x-ray spectroscopy, we demonstrated a bimodal height distribution with peaks at ~5 and ~20 nm and a control of both the lateral size distribution, peaked from ~100 to ~160 nm, and the amount of Ga–In intermixing in the QDs (up to 20%). Using photoluminescence (PL) spectroscopy in combination with circular polarization degree and time resolved micro-PL measurements, we demonstrated control of the emission energy, the intrinsic doping, and the emission decay of these In(Ga)P QDs. Using high-spatial-resolution near-field PL spectra and imaging of single dots, we demonstrated WL effects in dots having a population of up to nine electrons and a parabolic confinement down to ħω0 ~ 1 meV. We performed a self-consistent calculation of exciton transitions using an effective mass, mean field theory with an isotropic elasticity model to describe the effect of Ga–In intermixing on the emission properties of these dots; and we used calculations of shell splitting, using mean field Hartree–Fock approach and calculations of electron density distribution using configuration interaction approach, to described effects of enhancement of WL in non-circular dots with hard-wall potentials.

Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates

Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.

Effects of the substrate misorientation on the structural and optoelectronic characteristics of tensile GaInP quantum well laser diode wafer

Three tensile GaInP quantum well laser diode wafers were grown in the same run by low-pressure metalorganic vapor phase epitaxy on GaAs substrates misoriented by 10°, 15°, and 22° toward (1 1 1)A respectively. The photoluminescence peak wavelength and intensity of the active region, the strain mismatch and the doping carrier concentration of the epitaxial layers, the whole thickness and the surface morphology of the wafers were all found to be strongly dependent on the misorientation of the substrates. Considering the comprehensive effects of material, electrical, and optical properties, the 15° substrate was superior to the 10° substrate for the growth of shorter wavelength red-light laser diode wafer, while substrate with too large misorientation of 22° was not a good choice for the epitaxy of red-light laser diode wafer.

The role of surface kinetics on composition and quality of AlGaN

Metal–polar, Al-rich AlGaN films were grown on both single crystalline AlN and sapphire substrates. The role of surface morphology and surface kinetics on AlGaN composition is presented. With the reduced dislocation density of the films grown on AlN substrates, atomically smooth bilayer stepped surfaces are achieved with RMS roughness of less than 50pm for a 5×5µm2 AFM scan area. By controlling the surface supersaturation through adjusting the growth rate, a transition from 2D nucleation to step flow was observed. The critical misorientation angle for step-bunching in nominal Al0.70Ga0.30N grown with a growth rate of 600nm/h on AlN substrates was found to be 0.4°. The composition of bilayer stepped AlGaN was strongly dependent on substrate misorientation angle, where a compositional variation by a factor of two for a change in misorientation angle from 0.05 to 0.40° was observed; this is explained by the different surface diffusion lengths of Ga and Al. Step-bunching resulted in strong compositional inhomogeneity as observed by photoluminescence and scanning transmission electron microscopy studies.

Characterization of M-plane GaN thin films grown on misoriented γ-LiAlO2 (100) substrates

M-plane GaN thin films were grown on 11° misoriented γ-LiAlO2 substrates without peeling off or cracking by plasma-assisted molecular beam epitaxy. Because of anisotropic growth kinetics, which leads to an anisotropic compressive in-plane strain in the M-plane GaN films, the surface presents a rough morphology with worse crystal quality. The crystal quality of sample was optimally improved, XRD rocking curve FWHM of which is about 900arcsec, by raising growth temperature to 800°C with proper Ga/N flux ratio. As the crystal quality was improved, the polarization ratio decreased from the unity (less than 0.8) which could be attributed to the effect of exciton localization due to the partial increased in-plane strain.