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Thin Ga2O3 films were deposited by plasma-assisted molecular beam epitaxy on SrTiO3 (001) and SrTiO3-buffered Si (001) substrates. Examination using reflection-high-energy electron diffraction, x-ray diffraction, and transmission electron microscopy shows a consistent picture of (100)- and ( 1 ¯ 12) -oriented β-Ga2O3 grains. The structural alignments are β-Ga2O3[010] || STO ⟨110⟩ and β-Ga2O3 [021] || STO ⟨100⟩, respectively, each with four in-plane rotational domain variants. Successful integration of epitaxial β-Ga2O3 with Si could enable major opportunities for monolithically integrated Ga2O3 technology by serving as a high-quality seed layer for further epitaxial growth. [ABSTRACT FROM AUTHOR]

Changes in valence band offsets (VBOs) as a result of annealing of heterostructures of atomic layer deposited Al2O3 on (InxGa1 − x)2O3 (where x = 0.25–0.75), grown by pulsed laser deposition, are reported. The heterostructures have been annealed at 600 °C to simulate the expected thermal budget during device fabrication. The VBOs decrease significantly as a result of annealing, with the change being larger at higher indium concentrations. The decrease in VBO ranges from −0.38 eV for (In0.25Ga0.75)2O3 to −1.28 eV for (In0.74Ga0.26)2O3 and is likely due to increased interfacial disorder at the heterointerface as well as phase differences between gallium-rich samples and indium-rich samples. After annealing, the band alignment remains type I (nested gap) for x = 0.25, 42, and 60 but becomes type II for the (In0.74Ga0.26)2O3 sample. [ABSTRACT FROM AUTHOR]

The EuO/SrTiO3 heterojunction is a promising combination of a ferromagnetic material and a two-dimensional electron system. We explore the deposition of Eu metal on SrTiO3/Si pseudo-substrates, with varying SrTiO3 (STO) thickness, under ultrahigh vacuum conditions. By varying the thickness of the STO layer (2-10 nm) and the deposition temperature (20-300 °C), we investigate the process by which oxygen is scavenged from STO by Eu. In situ x-ray photoelectron spectroscopy is used to investigate the electronic structure of the nominal Eu/STO/Si stack. We find that as a result of Eu deposition, epitaxial EuO is formed on thick STO (6-10 nm), leaving behind a highly oxygen-deficient SrTiO3-δ layer of ∼4 nm in thickness. However, if the thickness of the STO layer is comparable to or less than the scavenging depth, the crystal structure of STO is disrupted and a solid state reaction between Eu, Si, and STO occurs when the deposition is done at a high temperature (300 °C). On the other hand, at a low temperature (20 °C), only a 1-2 nm-thick EuO interlayer is grown, on top of which the Eu metal appears to be stable. This study elucidates the growth process under different conditions and provides a better understanding and control of this system. [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth of crystalline SrZrO3 (SZO) on Ge (001) by atomic layer deposition is reported. Ge (001) surfaces are pretreated with 0.5-monolayers (ML) of Ba and an amorphous ∼3-nm SZO layer is grown from strontium bis(triisopropylcyclopentadienyl), tetrakis (dimethylamido) zirconium, and water at 225 °C. This ∼3-nm layer crystallizes at 590 °C and subsequent SZO growth at 225 °C leads to crystalline films that do not require further annealing. The film properties are investigated using X-ray photoelectron spectroscopy, x-ray diffraction, aberration-corrected electron microscopy, and capacitance-voltage measurements of metal-oxide semiconductor capacitor structures. Capacitance-voltage measurements of the SrZrO3/Ge heterojunctions reveal a dielectric constant of 30 for SrZrO3 and a leakage current density of 2.1 × 10−8 A/cm2 at 1 MV/cm with an equivalent oxide thickness of 0.8 nm. Oxygen plasma pretreatment of Ge (001), Zintl layer formation with 0.5 ML Ba, and atomic deuterium post-growth treatment were explored to lower interface trap density (Dit) and achieved a Dit of 8.56 × 1011 cm−2 eV−1. [ABSTRACT FROM AUTHOR]

The (110) plane of Co3O4 spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co3+ species at the surface. However, experimental studies of Co3O4 (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10-250Å) Co3O4 films grown by molecular beam epitaxy in the polar (110) direction on MgAl2O4 substrates. Reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and transmission electron microscopy measurements attest to the high quality of the as-grown films. Furthermore, we investigate the electronic structure of this material by core level and valence band x-ray photoelectron spectroscopy, and first-principles density functional theory calculations. Ellipsometry reveals a direct band gap of 0.75 eV and other interband transitions at higher energies. A valence band offset of 3.2 eV is measured for the Co3O4/MgAl2O4 heterostructure. Magnetic measurements show the signature of antiferromagnetic ordering at 49K. FTIR ellipsometry finds three infrared-active phonons between 300 and 700 cm-1. [ABSTRACT FROM AUTHOR]

In this work, thin epitaxial layers of dielectric barium titanate (BaTiO3 or BTO) were grown on Nb-doped strontium titanate (001) substrates using either molecular beam epitaxy or atomic layer deposition and then electrically stressed to the point of breakdown. The BTO layer thicknesses were in the range of 20–60 nm, and typical breakdown fields were in the range of 1.5–3.0 MV/cm. Electron microscopy and electron energy-loss spectroscopy (EELS) were used to provide information about the degradation mechanism. High-resolution imaging revealed widespread structural damage in the BTO films after breakdown had occurred, with substantial polycrystallinity as well as amorphous regions. EELS analysis of the stressed films showed characteristic signatures of valence change in the Ti L23 EELS spectra associated with the accumulation of oxygen vacancies. Stressed heterostructures that had been patterned by electron lithography showed similar trends, including degraded crystallinity as well as oxygen loss. [ABSTRACT FROM AUTHOR]

Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between the GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710 °C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620 °C. Ex situ atomic force microscopy and transmission electron microscopy analyses showed that the dot size distribution was bimodal. A thin GaN continuous layer of ∼ three monolayers thick was observed by transmission electron microscopy on the sample grown at a substrate temperature of 620 °C, but no such layer was observed for the substrate temperature of 710 °C. This suggests that there is little mobility of Ga atoms in contact with the sapphire substrate at the lower temperature so that they cannot easily diffuse to nearby droplets and instead form a thin layer covering the surface. [ABSTRACT FROM AUTHOR]

GaN/Al0.2Ga0.8N multiple quantum wells (MQWs) were grown by molecular beam epitaxy on randomly textured and atomically smooth (0001) GaN templates. Smooth and textured GaN templates were deposited on (0001) sapphire substrates by varying the III/V ratio and the substrate temperature during growth by the hydride vapor-phase epitaxy method. We find that the MQWs replicate the texture of the GaN template, which was found to have a Gaussian distribution. The peak photoluminescence intensity from the textured MQWs is always higher than from the smooth MQWs and for GaN (7 nm)/Al0.2Ga0.8N (8 nm) MQWs, it is 700 times higher than that from similarly produced MQWs on smooth GaN templates. This result is attributed partly to the enhancement in light extraction efficiency and partly to the enhancement in internal quantum efficiency. The origin of the increase in internal quantum efficiency is partly due to the reduction of the quantum-confined Stark effect, since the polarization vector intersects the quantum well (QW) planes at angles smaller than 90°, and partly due to the charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs. [ABSTRACT FROM AUTHOR]

We report on the effectiveness of porous TiN nanonetworks on the reduction of threading dislocations (TDs) in GaN grown by metal-organic vapor-phase epitaxy (MOVPE). The porous TiN networks were formed by in situ annealing of thin-deposited Ti films deposited ex situ on GaN templates within the MOVPE growth chamber. Different annealing parameters in relation to surface porosity of TiN networks were investigated. Transmission electron micrographs indicated dislocation reduction by factors of up to 10 in GaN layers grown on the TiN nanonetwork, compared with a control sample. TiN prevented many dislocations present in the GaN templates from penetrating into the upper layer. Microscale epitaxial lateral overgrowth of GaN above TiN also contributed to TD reduction. The surface porosity of the TiN network had a strong impact on the efficiency of TD reduction. X-ray-diffraction and time-resolved photoluminescence measurements further confirmed the improved GaN quality. [ABSTRACT FROM AUTHOR]

This paper reviews our recent investigations of compound semiconductors and heterovalent interfaces using the technique of aberration-corrected scanning transmission electron microscopy. Bright-field imaging of compound semiconductors with a collection angle that is comparable in size to the incident-beam convergence angle is demonstrated to provide better atomic-column visibility for lighter elements in comparison with the more traditional high-angle annular-dark-field approach. Several pairs of Group II–VI/Group III–V compound semiconductors with zincblende structure have been studied in detail. These combinations are all valence-mismatched (i.e., heterovalent), and include CdTe/InSb (Δa/a ≤ 0.05%), ZnTe/InP (Δa/a = 3.8%), and ZnTe/GaAs (Δa/a = 7.4%). CdTe/InSb (001) interfaces are observed to be defect-free with a slight lattice contraction at the interface plane. For interfaces with larger lattice-parameter mismatch, the primary interfacial defects are identified as Lomer edge dislocations and perfect 60° dislocations. However, the atomic structure of the dislocation cores has not yet been unambiguously determined. [ABSTRACT FROM AUTHOR]

The integration of dissimilar materials is highly desirable for many different types of device applications but often challenging to achieve in practice. The unrivalled imaging capabilities of the aberration-corrected electron microscope enable enhanced insights to be gained into the atomic arrangements across heterostructured interfaces. This paper provides an overview of our recent observations of oxide-semiconductor heterostructures using aberration-corrected high-angle annular-dark-field and large-angle bright-field imaging modes. The perovskite oxides studied include strontium titanate, barium titanate, and strontium hafnate, which were grown on Si(001) and/or Ge(001) substrates using the techniques of molecular-beam epitaxy or atomic-layer deposition. The oxide layers displayed excellent crystallinity and sharp, abrupt interfaces were observed with no sign of any amorphous interfacial layers. The Ge(001) substrate surfaces invariably showed both 1× and 2× periodicity consistent with preservation of the 2 × 1 surface reconstruction following oxide growth. Overall, the results augur well for the future development of functional oxide-based devices integrated on semiconductor substrates. [ABSTRACT FROM AUTHOR]

Thick GaN templates (>50 µm) were grown by hydride-vapor-phase epitaxy (HVPE) on the r-plane of sapphire. While X-ray diffraction indicates that the GaN grows with its a-plane parallel to the r-plane of sapphire, the surface has a triangular morphology of 120º, which is the result of the faster growth rate of the a-plane compared to the m-plane. Electron microscopy studies indicate that these GaN templates have a high concentration of threading defects (>1010 cm-2) and basal plane stacking faults (7x105 cm-1). Several identical deep-UV emitting Al0.7Ga0.3N/AlN multiple quantum wells (MQWs) were grown on such GaN templates by molecular-beam epitaxy (MBE). The wells were grown under more gallium than required by stoichiometry, which changes the growth mode from physical vapor deposition to liquid phase epitaxy. This growth mode leads to deep band structure potential fluctuations. The structure and microstructure of these MQWs were evaluated by transmission electron microscopy (TEM) and found to have even higher density of threading defects than the GaN template. In spite of this, the internal quantum efficiency (IQE) of these MQWs was estimated from the temperature dependence of the cathodoluminescence spectra to be 87%. This remarkable result was attributed to the deep band structure potential fluctuations introduced by the liquid-phase epitaxy growth mode as well as the high concentration of basal plane stacking faults. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Usingthe Au-seeded vapor–liquid–solid technique, epitaxialsingle-crystal Si nanowires (NWs) can be grown laterally along Si(111)substrates that have been miscut toward [112̅]. The ratio oflateral-to-vertical NWs increases as the miscut angle increases andas disilane pressure and substrate temperature decrease. By exploitingthese trends, conditions can be identified whereby all of the depositedAu seeds form lateral NWs. Growth is guided along the nanofacetedsubstrate via a mechanism that involves pinning of the trijunctionat the liquid/solid interface of the growing nanowire. [ABSTRACT FROM AUTHOR]

GaN(Si)/AlInN multiple quantum wells were grown on GaN/Al2O3 (0001) templates by metalorganic vapor-phase epitaxy. Transmission electron microscopy observations showed well-defined GaN quantum wells and AlInN barrier layers. Electrostatic potential profiles across the heterostructure have been measured using off-axis electron holography. A polarization-induced electric field with magnitude of ∼2.2 ± 0.1 MV/cm was measured across the GaN quantum wells, in reasonable agreement with simulated values. However, the measured fields across the AlInN barriers were considerably less than predicted from simulations: possible reasons are briefly discussed. [ABSTRACT FROM AUTHOR]

We report the development of Al0.7Ga0.3N/AlN quantum wells with high internal quantum efficiency. All samples had identical well and barrier thickness but the III/V flux ratio was varied during growth by increasing the Ga flux. The luminescence spectra show single peaks which vary from 220 nm (III/V∼1) to 250 nm (III/V>1) with internal quantum efficiency varying from 5% to 50%, respectively. To account for these results, a growth model was proposed in which at III/V∼1 the growth proceeds via vapor phase epitaxy, while at III/V>1 the growth proceeds via liquid phase epitaxy. [ABSTRACT FROM AUTHOR]

The authors report the growth of semipolar [formula] GaN films on nominally on-axis [formula] m-plane sapphire substrates using metal organic chemical vapor deposition. High-resolution x-ray diffraction (XRD) results indicate a preferred (1122) GaN orientation. Moreover, epitaxial lateral overgrowth (ELO) of GaN was carried out on the (1122) oriented GaN templates. When the ELO stripes were aligned along [1120]sapphire, the Ga-polar wings were inclined by 32° with respect to the substrate plane with smooth extended nonpolar a-plane GaN surfaces and polar c-plane GaN growth fronts. When compared with the template, the on-axis and off-axis XRD rocking curves indicated significant improvement in the crystalline quality by ELO for this mask orientation (on-axis 1700 arc sec for the template, 380 arc sec for the ELO sample, when rocked toward the GaN m axis), as verified by transmission electron microscopy (TEM). For growth mask stripes aligned along [0001]sapphire with GaN m-plane as growth fronts, the surface was composed of two {1011} planes making a 26° angle with the substrate plane. For this mask orientation XRD and TEM showed no improvement in the crystalline quality by ELO when compared to the non-ELO template. [ABSTRACT FROM AUTHOR]

The microstructure of InxAl1-xN/GaN heterostructures (where x∼0.13–0.19), grown by molecular beam epitaxy, was investigated by transmission electron microscopy. Observations in the cross-section and plan-view geometries show evidence for lateral phase separation originating at the GaN surface that results in a vertical honeycomblike structure within the InAlN layers. The lateral dimensions of the honeycomb cells are ∼5–10 nm. The vertical walls are In rich with a width of ∼1–2 nm and align roughly perpendicular to <1120> and <1100> directions. The phase separation is attributed to random compositional fluctuations during the early stages of growth, possibly associated with misfit-strain relaxation. [ABSTRACT FROM AUTHOR]

We report the growth of epitaxial DySi2 nanowires (NW) with a single orientation on miscut Si(111). Using high-resolution electron microscopy, we determine that the islands are hexagonal DySi2 with orientation DySi2(0001)∥Si(111), corresponding to a near-perfect lattice match. The NW islands develop extended defects that correlate perfectly with individual step bunches at the buried interface, produced during growth. By contrast, islands grown on step-free substrates develop a broad, two-dimensional shape with no defects. We suggest that the NW shape results from the energy cost of extended defects, which inhibits growth across step edges. [ABSTRACT FROM AUTHOR]

We report on the realization of InGaAs/InAlAs quantum-cascade lasers grown by metalorganic vapor phase epitaxy operating in continuous wave with low-threshold current densities at temperatures as high as 188 K. Threshold current densities of 950 A/cm2 and output powers of 125 mW are measured at 80 K, while 3 mW of continuous output power are measured at 180 K, with a threshold of 2.5 kA/cm2. In pulsed mode, peak output powers of more than 0.4 W were obtained at 80 K and of 160 mW at 300 K with thresholds of 700 A/cm2 and 2.75 kA/cm2, respectively. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistor structures have been grown by plasma-assisted molecular beam epitaxy on semi-insulating 4H-SiC utilizing an AlN nucleation layer. The electron Hall mobility of these structures increases from 1050 cm2/V s to greater than 1450 cm2/V s when the Al/N flux ratio during the growth of the nucleation layer is increased from 0.90 to 1.07. Buffer leakage currents increase abruptly by nearly three orders of magnitude when the Al/N ratio increases from below to above unity. Transmission electron microscopy indicates that high buffer leakage is correlated with the presence of stacking faults in the nucleation layer and cubic phase GaN in the buffer, while low mobilities are correlated with high dislocation densities. [ABSTRACT FROM AUTHOR]

We report epitaxial growth of Ge nanopillars (NPs) on Si (100) by vapor-liquid-solid (VLS) growth from digermane. This growth morphology is characterized by short, low-aspect-ratio pillars and is markedly different from the long, narrow nanowires (NWs) previously reported for VLS growth. The NP growth mode occurs at low digermane pressures. It is attributed to surface-diffusion-induced lateral growth in combination with an insufficient Ge concentration gradient in the AuGe eutectic to catalyze NW growth. High resolution electron microscopy confirms that the NPs are epitaxial with the Si (100) substrate and are fully relaxed and strain free. [ABSTRACT FROM AUTHOR]

Lomer edge dislocations formed at Ge/Si(001) hetero-interfaces have been imaged with a 1.25-MeV atomic-resolution electron microscope. The dislocation cores were primarily asymmetrical, and they were located close to the mean position of the interface, which was not structurally abrupt due to Ge–Si interdiffusion at the growth temperature of 550 °C. Structural models of the asymmetric dislocation cores could be derived directly from the experimental micrographs and image simulations were then used to validate the image interpretation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An approach based on the technique of convergent-beam electron diffraction (CBED) has been used to determine the elemental composition of a pseudomorphic GaN/In[sub x]Ga[sub 1-x]N/GaN quantum-well structure on the nanometer scale. Areas of triangles formed by intersecting higher order Laue-zone (HOLZ) lines are highly sensitive to lattice-parameter variations. By calculating the ratio of triangle areas, the local In concentration is estimated to within ±0.5% once lattice expansion in the growth direction has been taken into account. Moreover, shifts in the HOLZ-line positions as the CBED probe is moved along the quantum well provide a simple and rapid indication of local fluctuations in In content. The technique is applicable to other pseudomorphically strained epitaxial layers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report spontaneous chemical ordering of Mn[sub 0.52]Pd[sub 0.48] films, grown by molecular-beam epitaxy on body-centered-cubic Fe(001) films. The bilayers were grown at room temperature onto a seeding structure of Ag(001)/Fe(001)/GaAs(001). X-ray, neutron, and electron diffraction studies confirm extensive chemical ordering of the MnPd to the L1[sub 0] antiferromagnetic phase which grows as a twinned film with the tetragonal c axis in the film plane. The Fe film exhibits a unidirectional exchange bias and we find no pronounced difference in magnetic structure of the biased Fe layer at the ascending and descending crossing fields where the net moment along the applied field axis is zero. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Details the growth of crystalline Ge-C materials with unusual morphologies that depend on the molecular design of the precursor and the C concentration using chemical precursors. Formation of coherent carbide islands after epitaxial growth of Ge[sub 1-x]C[sub x] on (100)Si; Lower reaction temperatures resulting in low growth rate of epitaxial Ge[sub 1-x]C[sub x].

The microstructure of heteroepitaxial CdTe (001) and ZnTe(001) epilayers grown on Ge(001) buffer layers by molecular beam epitaxy has been characterized using electron microscopy. Apart from occasional {111} stacking faults originating at the interfacial region, the prevailing defects present in both systems are identified by high-resolution imaging as perfect Lomer edge dislocations with Burgers vectors of the type a/2<110> parallel to the interface plane, which are indicative of well-relaxed material. Double-crystal rocking-curve measurements using Ge(001) buffer layers give full-width-at-half-maximum values of 210 arc-sec for a 7.5μm thick ZnTe film and 125 arc-sec for a 12μm thick CdTe film. Use of the Ge buffer layers on Si(001) substrates represents a valuable precursor for eventual growth of mercury cadmium telluride since this allows the substrate orientation to be maintained. The buffer layer also permits a substantial reduction of the in situ annealing temperature needed for substrate oxide removal. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The microstructure of p-n device structures grown by liquid-phase epitaxy (LPE) on CdZnTe substrates has been evaluated using transmission electron microscopy (TEM). The devices consisted of thick (∼21-µm) n-type layers and thin (∼1.6-µm) p-type layers, with final CdTe (∼0.5 µm) passivation layers. Initial observations revealed small defects, both within the n-type layer (doped with 8 x 1014/cm³ of In) and also within the p-type layer but at a much reduced level. These defects were not visible, however, in cross-sectional samples prepared by ion milling with the sample held at liquid nitrogen temperature. Only isolated growth defects were observed in samples having low indium doping levels (2 x 1014/cm³). The CdTe passivation layers were generally columnar and polycrystalline, and interfaces with the p-type HgCdTe layers were uneven. No obvious structural changes were apparent in the region of the CdTe/HgCdTe interfaces as a result of annealing at 250°C. [ABSTRACT FROM AUTHOR]

High quality epitaxial III-N semiconductor films, ranging in thickness from 300 to 900 Å, have been grown using A[sup 3]Σ[sub u][sup +] metastable nitrogen molecules. The work employed a corona discharge supersonic free-jet to generate a molecular beam containing exclusively the A[sup 3]Σ[sub u][sup +] activation state in an otherwise ground state N[sub 2] beam. AlN films were grown on 6H-SiC(0001) and Si(001) substrates. GaN films were grown on the same substrates and on buffer layers of AlN deposited in situ on 6H-SiC(0001). The N-atom incorporation efficiency (the number of N atoms attaching to a III-N surface per incident A[sup 3]Σ[sub u][sup +] molecule) approached 100% and was independent of substrate temperature from 600 to 900 °C, implying direct molecular chemisorption of the A[sup 3]Σ[sub u][sup +]. These measurements support theoretical predictions that A[sup 3]Σ[sub u][sup +] is an ideal precursor for III-N growth. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: We review the topic of self-assembled endotaxial silicide nanowires on silicon. Crystallographic orientation, lattice mismatch and average dimensions are discussed for a variety of systems including Ti, Mn, Fe, Co, Ni, Pt and several rare earths on Si(100), Si(111) and Si(110) surfaces. In situ observations of growth dynamics support a constant-shape growth model, in which length, width and thickness all change in proportion as the nanowire grows, with thermally activated, facet-dependent rates. [Copyright &y& Elsevier]

Homoepitaxial ZnO films have been grown via metalorganic vapor-phase epitaxy on O- and Zn-terminated basal-plane-oriented ZnO substrates. Maps of on-axis X-ray rocking curves obtained over 2-in-diameter ZnO{0 0 0 1} wafers, diced from boules produced by vapor phase transport, revealed well-defined areas that ranged from <50 to >1050 arcsec FWHM, indicating the presence of tilted domains. This macrostructure was manifested in all the homoepitaxial ZnO films deposited on these wafers. The films grown on O-terminated ZnO surfaces were initially dense. However, they changed to a textured polycrystalline microstructure after &ap;100 nm and possessed a surface roughness of 7.3 nm. By contrast, the films grown on the Zn-terminated surface under the same conditions were fully dense, without texture and appeared to be monocrystalline with a significantly improved surface roughness of 3.4 nm. Cross-sectional transmission electron microscopy of the wafers revealed high densities of edge dislocations and stacking faults with associated Frank partial dislocations. [Copyright &y& Elsevier]

The growth of titanium silicide islands formed by reactive deposition of Ti on Si(1 1 1) at T∼850 °C has been studied using atomic force microscopy and transmission electron microscopy. The predominant shape is very long and narrow, and can be considered to be a nanowire (NW). Other flat-topped structures coexist with the NWs, including small equilateral triangles and large rectangular plates. Most NWs are oriented along Si〈2 2 0〉 directions, with typical dimensions 20 nm wide, 10 nm high and several microns long. A minority of NWs are oriented along Si〈2 2 4〉. These latter tend to break up into chains of small segments with regular size and spacing. Growth at lower temperature or higher deposition rate results in smaller and more numerous NWs. Length appears to be limited by intersection with other NWs oriented 120° apart. The junction between NWs appears to be incoherent in most cases. The triangular islands are positively identified as fully relaxed C54 TiSi2, while the chains are relaxed C49 TiSi2. The dominant NW structure is incommensurate and is tentatively identified as C49 TiSi2. [Copyright &y& Elsevier]

Highlights • Defect creation in GaP-Si(0 0 1) structures was investigated by XRD and TEM. • Anti-phase boundaries (APBs) were observed in GaP-Si(0 0 1) structures. • APBs increased local elastic stress and stimulated creation of SFs and MTs. • MBE growth conditions postpone onset of relaxation of GaP up to >250 nm thick. Abstract This work investigates defect formation and evolution associated with the deposition of GaP layers on precisely oriented Si(0 0 1) substrates. The GaP layers were grown with thicknesses ranging from ∼37 nm to ∼2 µm at a growth rate of 0.52 μm/hr using molecular beam epitaxy (MBE). The crystallinity of thin (37-nm) MBE-grown GaP layers was also compared with thin GaP layers grown by migration-enhanced epitaxy (MEE). The MBE growth procedure was shown to postpone relaxation of the epitaxial GaP layers up to a thickness of ∼250 nm. Detailed analysis of high-resolution X-ray diffraction patterns and comparison with cross-sectional transmission electron micrographs clarified the defect formation mechanism. Thin GaP layers showed very low defect densities except for anti-phase boundaries, whereas substantial threading defects predominated in the thicker, noticeably relaxed structures. [ABSTRACT FROM AUTHOR]

Barium titanate BaTiO 3 (BTO) thin films were epitaxially grown at 225 °C on 2 × 1-reconstructed Ge(001) surfaces via atomic layer deposition (ALD). Approximately 2 nm of BTO film was grown directly on Ge(001) as an amorphous film. Electron diffraction confirmed the epitaxy of the BTO films after post-deposition annealing at 650 °C. Additional BTO layers grown on the crystalline BTO/Ge(001) film were crystalline as-deposited. X-ray diffraction indicated that the epitaxial BTO films had a c -axis out-of-plane orientation, and the abrupt BTO/Ge interface was preserved with no sign of any interfacial germanium oxide. Scanning transmission electron microscopy provided evidence of Ba atoms occupying the troughs of the dimer rows of the 2 × 1-reconstructed Ge(001) surface, as well as preservation of the 2 × 1-reconstructed Ge(001) surface. This study presents a low-temperature process to fabricate BTO/Ge heterostructures. [ABSTRACT FROM AUTHOR]

A series of three CdTe/Mg x Cd 1− x Te ( x ~0.24) double heterostructures grown by molecular beam epitaxy on InSb (001) substrates at temperatures in the range of 235–295 °C have been studied using conventional and advanced electron microscopy techniques. Defect analysis based on bright-field electron micrographs indicates that the structure grown at 265 °C has the best structural quality of the series, while structures grown at 30 °C lower or higher temperature show highly defective morphology. Geometric phase analysis of the CdTe/InSb interface for the sample grown at 265 °C reveals minimal interfacial elastic strain, and there is no visible evidence of interfacial defect formation in aberration-corrected electron micrographs of this particular sample. Such high quality CdTe epitaxial layers should provide the basis for applications such as photo-detectors and multi-junction solar cells. [ABSTRACT FROM AUTHOR]

Zintl phases are a class of intermetallic materials that have simultaneously ionic and covalent bonding resulting from charge transfer between two different atomic species. We present a combined first principles and experimental study of Zintl-phase SrA14, which is grown in thin film form on the perovskite oxide LaAlO3 using molecular beam epitaxy. The structural properties are investigated using reflection-high-energy electron diffraction, x-ray diffraction, and cross-section transmission electron microscopy, which reveal relaxed epitaxial island growth. Photoelectron spectroscopy measurements verify the Zintl-Klemm nature of the bonding in the material and are utilized to determine the band offset and the work function of SrAl4, while transport measurements confirm its metallic behavior. The experimentally observed properties are confirmed using density functional calculations. [ABSTRACT FROM AUTHOR]

This Article describes the development of an optimized chemistry-based synthesis method, supported by a purpose-built reactor technology, to produce the next generation of Ge1-x-ySixSny materials on conventional Si(100) and Ge(100) platforms at gas-source molecular epitaxy conditions. Technologically relevant alloy compositions (1-5% Sn, 4-20% Si) are grown at ultralow temperatures (330-290 °C) using highly reactive tetragermane (Ge4H10), tetrasilane (Si4H10), and stannane (SnD4) hydride precursors, allowing the simultaneous increase of Si and Sn content (at a fixed Si/Sn ratio near 4) for the purpose of tuning the bandgap while maintaining lattice-matching to Ge. First principles thermochemistry studies were used to explain stability and reactivity differences between the Si/Ge hydride sources in terms of a complex interplay among the isomeric species, and provide guidance for optimizing process conditions. Collectively, this approach leads to unprecedented control over the substitutional incorporation of Sn into Si-Ge and yields materials with superior quality suitable for transitioning to the device arena. We demonstrate that both intrinsic and doped Ge1-x-ySixSny layers can now be routinely produced with defect-free microstructure and viable thickness, allowing the fabrication of high-performance photodetectors on Ge(100). Highlights of these new devices include precisely adjustable absorption edges between 0.87 and 1.03 eV, low ideality factors close to unity, and state-of-the-art dark current densities for Ge-based materials. Our unequivocal realization of the "molecules to device" concept implies that GeSiSn alloys represent technologically viable semiconductors that now merit inclusion in the class of ubiquitous Si, Ge, and SiGe group IV systems. [ABSTRACT FROM AUTHOR]

Abstract: m-Plane GaN was grown selectively by metal–organic chemical vapor deposition (MOCVD) on patterned Si(112) substrates, where grooves aligned parallel to the Si〈110〉 direction were formed by anisotropic wet etching to expose the vertical Si{111} facets for growth initiation. The effect of growth conditions (substrate temperature, chamber pressure, and ammonia and trimethylgallium flow rates) on the growth habits of GaN was studied with the aim of achieving coalesced m-plane GaN films. The epitaxial relationship was found to be GaN(11̄00) || Si(112), GaN[0001] || Si[11–1], GaN[1̄1̄20] || Si[11̄0]. Among all growth parameters, the ammonia flow rate was revealed to be the critical factor determining the growth habits of GaN. The distribution of extended defects, such as stacking faults and dislocations, in the selectively grown GaN were studied by transmission electron microscopy in combination with spatially resolved cathodoluminescence and scanning electron microscopy. Basal-plane stacking faults were found in the nitrogen-wing regions of the laterally overgrown GaN, while gallium-wings were almost free of extended defects, except for the regions near the GaN/Si{111} vertical sidewall interface, where high dislocation density was observed. [ABSTRACT FROM AUTHOR]

Abstract: We report the observation of ordering in Al0.3Ga0.7N as part of an epitaxial lateral overgrowth (ELO) of GaN carried out using (112¯2) GaN templates grown by metal-organic chemical vapor deposition on m-plane sapphire. Transmission electron microscopy showed that the crystalline quality of the ELO GaN was greatly improved when the ELO SiO2 mask was patterned along the [112¯0]sapphire direction. The ELO GaN wings had an inclined columnar shape with smooth (0001) and (112¯0) facets. Layers of 1:1 [0001] ordered a-plane Al0.3Ga0.7N were observed on the a-plane GaN facets by high-resolution transmission electron microscopy and high-angle annular-dark-field scanning transmission electron microscopy. However, no ordering was observed for c-plane Al0.3Ga0.7N layers grown at the same time on the c-plane GaN facets. [Copyright &y& Elsevier]

Abstract: We report on the structural and electrical properties of AlGaN/GaN heterostructures grown by molecular beam epitaxy on low-dislocation-density, free standing GaN substrates grown by hydride vapor phase epitaxy. Structural characterization by atomic force microscopy, transmission electron microscopy, and X-ray diffractometry reveal a smooth surface morphology, coherent interfaces, an absence of dislocations generated in the epitaxial layers, and narrow X-ray peaks. Hall measurements indicate room temperature electron mobilities of 1750cm2/Vs at sheet densities of 1.1×1013 cm−2. High electron mobility transistors exhibit excellent electrical characteristics, including output power densities of 4.8W/mm at 10GHz, off-state breakdown voltages of up to 200V, and extrinsic cut-off frequencies of 36GHz on devices with 0.45-μm gate lengths. [Copyright &y& Elsevier]

Abstract: The effects of annealing on the microstructure of HgTe/Hg0.05Cd0.95Te/CdZnTe(211) superlattices (SLs) grown by molecular beam epitaxy have been investigated by high-resolution electron microscopy, and Z-contrast imaging was utilized to study the chemical abruptness of the HgTe/HgCdTe interfaces. Low-temperature annealing at 225 or 250°C induced interdiffusion, leading to changes in the well/barrier widths. The SLs became more defective even after 30min of annealing. The widths of the HgTe well layers increased and the widths of the HgCdTe barrier layers decreased dramatically. Thus, activation of p-type dopants such as arsenic through annealing will be difficult to achieve without degradation of electrical and optical properties. [Copyright &y& Elsevier]

This paper provides an overview of electron microscopy observations of epitaxial HgCdTe alloys. Growth of high quality Hg1−xCdxTe epilayers for infrared (IR) detector applications requires a detailed knowledge and control of the experimental factors causing defective material. The type of substrate, the substrate orientation, the substrate temperature during growth, and the Hg/Te flux ratio are factors that have a significant effect on the film morphology. Extensive characterization studies using electron microscopy methods have provided invaluable information about the connection between defect formation and the influence of specific growth parameters. The types of defects observed by electron microscopy include dislocations, twins and stacking faults, surface hillocks and crater defects, and precipitates, as well as spurious effects induced by sample preparation methods. By combining electron microscopy observations with other characterization methods such as in situ ellipsometry, Fourier Transform IR spectroscopy, and hole measurements, it should be possible to improve the quality of HgCdTe epilayers still further to meet the demanding requirements of future generation large format focal-plane arrays. [Copyright &y& Elsevier]