Misoriented Si Research Articles

Direct Heteroepitaxial Growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) Substrates by MBE

AbstractEpitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0–8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x ray FWHM as low as 55 arcseconds and average etch pit densities of 5 × 106 cm−2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.

Morphology of monatomic step edges on vicinal Si(001).

The roughness of monatomic A- and B-type step edges on 0.5\ifmmode^\circ\else\textdegree\fi{} misoriented Si(001) has been analyzed on an atomic scale with scanning tunneling microscopy. On small length scales, measured along the step edge (200 \AA{}), one-dimensional random-walk behavior is observed for both types of step edges. For the rough B-type step edge we also found evidence for waviness of the edge. The period of this wave is about 100 dimer-row spacings (\ensuremath{\approxeq}750--800 \AA{}). The energetic step-step interaction and entropic repulsion, which both scale as 1/${\mathit{L}}^{2}$ (L is the average terrace length), are estimated to be about 0.03--0.06 and 0.2 meV per dimer-row spacing, respectively, for a 0.5\ifmmode^\circ\else\textdegree\fi{} misoriented surface. These interactions are approximately three orders of magnitude smaller compared to the kink formation energies which are 0.1--0.2 eV. Despite the weak strength of energetic and entropic step-step interactions, these long-range interactions have a profound effect on the step-edge morphology, e.g., the distribution of terrace lengths and the long-range waving of the rough B-step edge.

Characterization of Antiphase Domain in GaP on Misoriented (001) Si Substrate Grown by Metalorganic Chemical Vapor Deposition

Antiphase domains (APD's) in GaP grown on (001) Si with different misorientation angles (0-6?) have been characterized by transmission electron microscopy (TEM) and etch pit observation. The self-annihilation of APD during growth is observed for GaP grown on exactly (001), 1?-off (001) and 2?-off (001) Si substrates, using TEM. A part of the APD is propagated to the surface in the case of exactly (001) and 1?-off (001) Si substrates. All the APD's are annihilated in the early stage of growth for GaP grown on 2?-off Si. On the other hand, no APD has been detected for GaP grown on 4?-off and 6?-off Si. The GaP surface morphology and the etch pit density are greatly affected by the APD's generated at the interface even if they are annihilated during the growth.

BEHAVIOR OF STEP EDGES ON Si(001)

The morphology of monatomic step edges on vicinal Si (001) surfaces is briefly reviewed. With increasing miscut angle, the Si (001) surface exhibits an interesting sequence of phase transitions. For a miscut angle smaller than about 0.03°, a hilly structure with step loops is found, whereas a phase of wavy steps coexisting with a phase of straight steps is observed in the range of 0.03°–0.1°. If the miscut angle lies in the range of 0.1° up to about 3°, two types, one much straighter than the other, of monatomic step edges develop. For even larger miscut angles, a phase of straight biatomic step edges is found. The fundamental energetic parameters, like kink formation energies, step edge energies and step-step interactions, which govern the thermodynamic behavior are determined using Scanning Tunneling Microscopy (STM) images of 0.5° misoriented Si (001). Despite the weak strength of energetic and entropic step-step interactions as compared to the interactions along the step edge, i.e. the kink formation and step edge energies, they have a profound effect on the meandering of the step edges. Both entropic and energetic step-step interactions are proportional to L−2 (where L is the average terrace length). The behavior of the step edges at temperatures above room temperature will be addressed with the aid of a high-temperature STM. The freeze-out temperature, T f , of the monatomic step edges is estimated to be higher than 600–700 K. The temperature T f is significantly above the roughening temperature, Tr, of the step edges. This means that at room temperature, the monatomic step edges on vicinal Si (001) are always rough.

Direct molecular-beam epitaxial growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) substrates

Epitaxial structures of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0° to 8° towards the [011] direction. The films were characterized with x-ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Single-crystal CdZnTe(100) films comparable in structural quality to those obtained with growth on GaAs/Si composite substrates have been demonstrated on both 4° and 8° misoriented Si with the use of ZnTe buffer layers. X-ray rocking curves with FWHM less than 300 arcsec for ZnTe (400) and less than 160 arcsec for CdZnTe(400) have been obtained for as-grown films. Specular surface morphologies, superior to those obtained on GaAs/Si composite substrates, are also observed.

Structure of CdTe(111)B grown by MBE on misoriented Si(001)

Single domain CdTe(111)B has been grown on Si(001) substrates tilted 1o 2o, and 4o toward [110]. All the layers started with a double-domain structure, then a transition from a double- to a single-domain was observed by reflection high energy electron diffraction. A microscopic picture of this transition is presented. We also measured the tilt between CdTe(111)B and Si(001). The result does not follow the tilt predicted by the currently existing model. A new model of the microscopic mechanism of CdTe(111)B growth is presented. New evidence indicates that optimizing the tilt of the substrate surface is very crucial in improving the CdTe(111)B crystal quality.

CdTe(111) growth on misoriented Si(100) substrates by hot-wall epitaxy

CdTe(111) layers were grown directly on misoriented Si(100) substrates by hot-wall epitaxy. The structure and crystallinity of the layer were examined by reflection high-energy electron diffraction (RHEED), etch-pit observation and X-ray diffraction measurements. The strain in the layer was investigated by X-ray Bond method. The layers on misoriented Si(100) substrates are composed of twinted domains elongated parallel to the misoriented direction of the substrates. A 5 μm thick layer was deformed by biaxial tensile stress by the difference between thermal expansion coefficients of CdTe and Si. The strain is relaxed as the layer thickness increases.

Investigation of the defect structure of thin single-crystalline CoSi2 (B) films on Si(111) by transmission electron microscopy

Thin epitaxial single-crystalline B-type CoSi2 films (twin-oriented) have been grown in ultrahigh vacuum by stoichiometric codeposition of Co and Si on slightly misoriented (0.1°–0.3°) Si(111) substrates. The microstructure as well as the nature of interfacial defects has been investigated in detail by transmission electron microscopy. The defect structure is found to depend closely on the initial deposition parameters, annealing temperature, and the topography of the Si substrate. It will be shown that even during the early stages of layer growth, loss of coherence is obtained and lattice strain already starts to occur with the introduction of misfit dislocations with Burgers vector b=a/2〈110〉 inclined to the interface or with Burgers vector b=a/6〈112〉 parallel to it. It is demonstrated that ultrathin CoSi2 films with thickness of about 1 nm grown on slightly misoriented substrates with parallel surface steps, exhibit quite different defect structures at annealing temperatures between 300 °C and 550 °C. Control of the dislocation density has been obtained by applying a two-step growth procedure. CoSi2 layers grown to a thickness <hc (4–5 nm) exhibit line defects with Burgers vector b=a/6〈112〉 associated with interfacial misorientation-related steps. Above this thickness additional dislocations in the three equivalent directions are formed, indicating biaxial strain relaxation. In addition, calculations of the critical thickness hc of biaxial strain relaxation based on thermodynamic equilibrium theory are presented. It is shown that the observed critical thickness hc is in qualitative agreement with theoretical predictions.

Direct Heteroepitaxial Growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) Substrates by MBE

ABSTRACTEpitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0-8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x ray FWHM as low as 55 arcseconds and average etch pit densities of 5 x 106 cm−2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.

Tilt Deformation of Metalorganic Chemical Vapor Deposition Grown GaP on Si Substrate

The behavior of the stress and the deformation of a GaP layer grown on misoriented (001)Si was investigated for the thickness and the growth temperature. The compressive stress in the GaP layer decreased with increasing thickness up to 0.5 µm and then changed into the tensile stress. However, there was poor dependence of the tensile stress in a 1 µm-thick GaP layer on growth temperature. The tilt deformation of the GaP layer strongly depended on the growth temperature. It was found that the deformation strongly depended on the misfit strain in the GaP layer for a Si substrate at the growth temperature rather than the thermal strain, and that the tilt was under the influence of the atomic step on a Si substrate.

Tem Study of Temperature Influence on The Crystalline Quality of InGaAs/Si Epilayers

ABSTRACTA Transmission Electron Microscopy (TEM) study of In0.53Ga0.47As Molecular Beam Epitaxy films grown at different temperatures onto misoriented Si (100) substrates is presented. The evolution of the density of the different kind of defects is discussed as a function of the growth temperature in the range between 200 and 500° C. The results are compared with the characterization techniques of Double Crystal X-Ray Diffraction and Hall effect.

Faceting of LPE GaAs grown on a misoriented Si(100) substrate

By employing a special patterned mask, GaAs(100) facets have been formed and epitaxial lateral overgrowth (ELO) of GaAs was successfully achieved on a misoriented Si(100) substrate. After many trial and error experiments, two patterns of line seed arrangements were found to give a relatively good ELO. One is composed of short line seeds and the other of long line seeds in a star-like arrangement. When the first pattern was used and the orientation of the short line seeds was chosen as the direction of the substrate misorientation, a facet was easily formed and it was found that the facet goes from one end to the other of the line seed, since the step flow from the upper stream side is prevented by the presence of an oxide film which terminates on the end of the window. With the second pattern, facets were formed only on one side of the star, which has been explained by the non-uniformity of the supersaturation and the substrate misorientation. The best ELO ratio obtained so far by this technique is around 5.

Single-Crystal Growth of Al(110) on Vicinal Si(100) in Ultra-High-Vacuum Sputtering System

A single-crystal Al(110) film has, for the first time, been grown on a misoriented (100) Si substrate (4°off toward [011] direction) by using an ultra-high-vacuum sputtering system at 350°C without any additional high-temperature treatment. The growth mechanism of the single crystal on the vicinal Si surface is discussed based on our new model, in which the atomic steps play an important role.

Interface characterization of epitaxial Ag Films on Si(100) and Si(111) grown by molecular beam epitaxy

Silver films grown on Si(100), Si(111), and thin oxide layers by molecular beam epitaxy (MBE) have been studied using multiple analysis techniques, including X-ray diffraction (pole-figure method and double-crystal diffractometry), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and MeV He+ Rutherford backscattering spectrometry (RBS)/ channeling. Despite the large lattice mismatch (∼25 pct) between Ag and Si, high-quality Ag single-crystal films (surface minimum yield χmin = 6 to 10 pct) were grown on clean Si substrates. Ag(111) texture films were also grown on the oxide layers of Si(100) and Si(111) surfaces. The epitaxial Ag/Si interface was thermally stable up to at least 500 °C. The adhesion between Ag and the oxide layer was poor. The primary defects contained in the Ag/Si(111) were twins. The quantity of twinning depends on the film thickness and the substrate orientation. For both Ag/Si(100) and Ag/Si(111) epitaxial systems, a high-density defect region was contained in the Ag film within ∼1000 A of the interface. Silver films grown on misoriented Si(111) substrates (∼4 deg off normal) were misoriented by 0. 5 deg toward the surface normal.

Characterization of Interfacial Structure in Large Lattice Mismatch Heteroepitaxy: Ag/Si (111)

ABSTRACTThe interfacial structure of a large lattice mismatched (˜25%) (111) Ag-Si system was studied by using transmission electron diffraction (SADP - Selected Area Diffraction Pattern). The epitaxial films of Ag (600–1200Å) were grown by MBE on flat Si(111) and misoriented Si(1ll) surfaces. We have examined the interfacial structures of the Ag on 2° misoriented Si(111) using diffraction patterns of cross sectional view. Through a detail analysis of thelocation and shape of the diffraction spots, we can determine the epitaxial relationship between Ag and Si, the small tilt angle of Ag(111) planes withrespect to the misoriented Si(111), the period of the finite terrace size of the misoriented Si substrate, and the size of the ordered region in the Ag film. The O-lattice analysis developed by Bollmann has beenapplied to this interface andthe result is compared with the SADP observation.

Regular step arrays at the SiO 2/Si(111) interface

A set of slightly misoriented Si(11) wafers have been oxidized and annealed in different ways. After removal of the oxide the structure of the Si/SiO 2 interface has been studied by a high-resolution LEED system. The resulting LEED spots showed relatively sharp splitting for out-of-phase condition, indicating a nearly regular step array. The spot profiles are described precisely by a closed form terrace width distribution. The energy dependence of the spot profiles yields the vertical roughness of the samples. It can be shown that the selection of appropriate oxidation parameters decreases the deviations from the periodic structure.

CdTe/GaAs/Si substrates for HgCdTe photovoltaic detectors

CdTe epitaxial films have been grown on GaAs on (100) silicon by congruent evaporation on CdTe in ultrahigh vacuum. The (100)CdTe orientation is strongly preferred in growth on (100)GaAs/Si, in contrast with the (111)CdTe preference on (100)GaAs substrates. Growth of the (111) orientation requires special processing. The (100)GaAs epilayer grows on misoriented (100)Si with a lattice tilt of ∼0.04° (back toward normal) for each degree of silicon misorientation. A similar lattice tilt in CdTe growth, in combination with the variable misorientation of the three-dimensional as-grown GaAs epilayer, is probably responsible for a mosaic structure in CdTe epilayers on GaAs/Si. In (111)CdTe layers, rotational twinning can occur on unpolished GaAs/Si. With increasing GaAs/Si misorientations, increasing numbers of (100) twin inclusions can also be found. Chemical polishing prior to CdTe growth eliminates the mosaic and twinning problems in most cases.

Effect of Substrate Misorientation on Heteroepitaxy with Large Lattice Mismatch: Ag/Si(111)

AbstractEpitaxial films of Ag(111) were grown by Molecular Beam Epitaxy (MBE) on small angle misoriented Si(111) substrates. The surface normal was tilted 0 to 6° away from the Si(111) axis toward the [112] direction. The structure of the films was analyzed by x-ray diffraction and MeV He+ ion channeling. Despite a large lattice mismatch, good quality epitaxial films, 600–1200 Å thick, were grown on the misoriented Si substrates. Interestingly, the angle between the Si(111) axis of the substrate and the Ag(111) axis of the film (the misalignment angle) is not zero. In contrast to the perfect alignment on a flat substrate, the Ag(111) axis is tilted away from the Si(111) axis toward the surface normal. Axial MeV He+ ion channeling shows the misalignment angle (up to .6°) increases with substrate misorientation angle (~1/10 substrate misorientation angle).

Defect Structure Analysis of Thick Epitaxial Films with Very Large Lattice Mismatch: Ag/Si(1l1) and Ag/Si(001).

The structural perfection and defects of Ag films deposited by molecular beam epitaxy (MBE) on Si(ll1) and Si(001) substrates have been analyzed by x-ray diffraction, Rutherford Backscattering (RBS)/channeling and electron microscopy. In spite of the large lattice mismatch (∼25 %) between Ag and Si, relatively high-quality Ag single crystal films (6∼10 % surface minimum yield) were grown on both Si(111) and Si(001) substrates. The primary defects contained in the Ag/Si(111) were double-positioning twins. The quantity of twinning depends on the film thickness and the substrate condition. For both Ag/Si(111) and Ag/Si(001) epitaxial systems, a high density defect region was contained in the Ag film within ∼1000 A of the interface. Ag films grown on misoriented Si(l11) substrates ( 4° off normal ) were misoriented by 0.5° towards the surface normal. Possible explanations of these defect formations associated with the large lattice mismatch are presented.

Multilayer step formation after As adsorption on Si (100): Nucleation of GaAs on vicinal Si

We have used reflection high-energy electron diffraction to characterize the initial surface of misoriented Si (100) and then to follow the nucleation of GaAs. Measurement of the diffracted intensity along the length of the specular streak shows sharp structure due to an ordered array of steps. The initial surface contains monolayer steps. However, after exposing to an As4 flux above 650 °C, the surface morphology changes to multilayer steps with four times the original period. In contrast, below 650 °C, surface migration is inhibited and monolayer steps are retained. Subsequent growth of GaAs on either the monolayer- or multilayer-stepped surfaces yields single domain films. However, GaAs grown on the monolayer steps is misoriented toward the (111)A while GaAs grown on the multilayer steps is misoriented toward the (111)B.