Showing papers on "Epitaxy published in 2003"
TL;DR: In this article, a multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 μm on c-plane sapphire substrates.
Abstract: A multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 μm on c-plane sapphire substrates. We obtain reproducibly high electron mobilities from 115 up to 155 cm2/V s at 300 K in a narrow carrier concentration range from 2 to 5×1016 cm−3. The key issue of the multistep PLD process is the insertion of 30-nm-thin ZnO relaxation layers deposited at reduced substrate temperature. The high-mobility samples show atomically flat surface structure with grain size of about 0.5–1 μm, whereas the surfaces of low-mobility films consist of clearly resolved hexagonally faceted columnar grains of only 200-nm size, as shown by atomic force microscopy. Structurally optimized PLD ZnO thin films show narrow high-resolution x-ray diffraction peak widths of the ZnO(0002) ω- and 2Θ-scans as low as 151 and 43 arcsec, respectively, and narrow photoluminescence linewidths of donor-bound excitons of 1.7 meV at 2 K.
594 citations
TL;DR: In this paper, a unified model for thin film epitaxy where single crystal films with small and large lattice misfits are grown by domain matching epitaxy (DME) is presented.
Abstract: We present a unified model for thin film epitaxy where single crystal films with small and large lattice misfits are grown by domain matching epitaxy (DME). The DME involves matching of lattice planes between the film and the substrate having similar crystal symmetry. In this framework, the conventional lattice matching epitaxy becomes a special case where a matching of lattice constants or the same planes is involved with a small misfit of less than 7%–8%. In large lattice mismatch systems, we show that epitaxial growth of thin films is possible by matching of domains where integral multiples of major lattice planes match across the interface. We illustrate this concept with atomic-level details in the TiN/Si(100) with 3/4 matching, the AlN/Si(100)with 4/5 matching, and the ZnO/α−Al2O3(0001) with 6/7 matching of major planes across the film/substrate interface. By varying the domain size, which is equal to intregral multiple of lattice planes, in a periodic fashion, it is possible to accommodate addition...
530 citations
TL;DR: In this article, the p-type gallium nitride nanowires were synthesized using metal-catalyzed chemical vapor deposition (CVD) and were found to have single-crystal structures with a 〈0001〉 growth axis that is consistent with substrate epitaxy.
Abstract: Magnesium-doped gallium nitride nanowires have been synthesized via metal-catalyzed chemical vapor deposition. Nanowires prepared on c-plane sapphire substrates were found to grow normal to the substrate, and transmission electron microscopy studies demonstrated that the nanowires had single-crystal structures with a 〈0001〉 growth axis that is consistent with substrate epitaxy. Individual magnesium-doped gallium nitride nanowires configured as field-effect transistors exhibited systematic variations in two-terminal resistance as a function of magnesium dopant incorporation, and gate-dependent conductance measurements demonstrated that optimally doped nanowires were p-type with hole mobilities of ca. 12 cm2/V‚s. In addition, transport studies of crossed gallium nitride nanowire structures assembled from p- and n-type materials show that these junctions correspond to well-defined p-n diodes. In forward bias, the p-n crossed nanowire junctions also function as nanoscale UV-blue light emitting diodes. The new synthesis of p-type gallium nitride nanowire building blocks opens up significant potential for the assembly of nanoscale electronics and photonics. Semiconductor nanowires (NWs) have demonstrated significant potential as fundamental building blocks for nanoelectronic and nanophotonic devices and also offer substantial
497 citations
TL;DR: In this paper, the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates is described.
Abstract: We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I-V characteristics, with threshold voltage ~3.2V and low reverse leakage current ~10(-7)A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 mn is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500K and shown to originate from recombination within the ZnO.
445 citations
434 citations
TL;DR: In this paper, the mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters was studied using high-resolution x-ray diffraction.
Abstract: The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters is studied using high-resolution x-ray diffraction. The coherence lengths, the tilt, and the twist of the mosaic structure are determined utilizing data taken in different x-ray scattering geometries. The results of different models, which were applied, are then compared and discussed. The dislocation densities, obtained from the x-ray data, are compared with the results of plan-view transmission electron microscopy and atomic force microscopy.
333 citations
TL;DR: In this paper, a series of thin InN films down to 10 nm in thickness were prepared by molecular-beam epitaxy on either AlN or GaN buffers under optimized growth conditions.
Abstract: A series of thin InN films down to 10 nm in thickness were prepared by molecular-beam epitaxy on either AlN or GaN buffers under optimized growth conditions. By extrapolating the fitted curve of sheet carrier density versus film thickness to zero film thickness, a strong excess sheet charge was derived, which must come from either the surface or the interface between InN and its buffer layer. Since metal contacts, including Ti, Al, Ni, and a Hg probe, can always form an ohmic contact on InN without any annealing, it is determined that at least part of the excess charge is surface charge, which was also confirmed by capacitance–voltage measurements.
290 citations
TL;DR: In this article, a large-scale freestanding GaN wafer was obtained with a diameter of 45 mm and a mirror-like surface, and the dislocation density was evaluated by etch pit density measurement.
Abstract: We have developed a novel technique for preparing large-scale freestanding GaN wafers. Hydride vapor phase epitaxy (HVPE) growth of thick GaN layer was performed on a GaN template with a thin TiN film on the top. After the cooling process of the HVPE growth, the thick GaN layer was easily separated from the template by the assistance of many voids generated around the TiN film. As a result, a freestanding GaN wafer was obtained. The wafer obtained had a diameter of 45 mm, and a mirror-like surface. The-full-width-at-half-maximum (FWHM) of (0002) and (1010) peaks in the X-ray rocking curve profile were 60 and 92 arcsec, respectively. The dislocation density was evaluated at 5×106 cm-3 by etch pit density measurement.
260 citations
TL;DR: In this paper, an extended defect density reduction in m-plane GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase epitaxy was reported.
Abstract: This letter reports on extended defect density reduction in m-plane (11¯00) GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase epitaxy. Several dielectric mask patterns were used to produce 10 to 100 μm-thick, partially and fully coalesced nonpolar GaN films. X-ray rocking curves indicated the films were free of wing tilt. Transmission electron microscopy showed that basal plane stacking fault (SF) and threading dislocation (TD) densities decreased from 105cm−1 and 109cm−2, respectively, less than 3×103cm−1 and ∼5×106cm−2, respectively, in the Ga-face (0001) wing of the LEO films. SFs persisted in ⟨0001⟩-oriented stripe LEO films, though TD reduction was observed in the windows and wings. Band-edge cathodoluminescence intensity increased 2 to 5 times in the wings compared to the windows depending on the stripe orientation. SFs in the low TD density wings of ⟨0001⟩-stripe films did not appear to act as nonradiative recombination centers.
246 citations
TL;DR: Spectroscopic ellipsometry (SE) measurements were made on thin-film and single-crystal TiO2 anatase using a two-modulator generalized ellipsometer.
Abstract: Spectroscopic ellipsometry (SE) measurements were made on thin-film and single-crystal TiO2 anatase using a two-modulator generalized ellipsometer. The TiO2 films were epitaxially stabilized on a LaAlO3 substrate in the anatase crystal structure using reactive sputter deposition. The films were highly crystalline, possessing a “stepped surface” morphology indicative of atomic layer-by-layer growth. The SE results for the anatase film indicate that the material is essentially oriented with the c axis perpendicular to the substrate, but there is some anisotropy near the interface and the surface. Corrugations of the film surface, as observed using atomic force microscopy, are consistent with a surface structure needed to create cross polarization. Accurate values of the optical functions of crystalline anatase were obtained above and below the band edge using SE. Above the band edge, both the ordinary and extraordinary complex dielectric functions exhibited two critical points.
240 citations
TL;DR: The epitaxial growth of wideband gap cubic-phase MgxZn1−xO thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors was reported in this article.
Abstract: We report on the epitaxial growth of wide-band-gap cubic-phase MgxZn1−xO thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors. The challenges of large lattice and thermal expansion mismatch between Si and MgxZn1−xO have been overcome by using a thin SrTiO3 buffer layer. The heteroepitaxy of cubic-phase MgxZn1−xO on Si was established with epitaxial relationship of MgxZn1−xO(100)//SrTiO3(100)//Si(100) and MgxZn1−xO[100]//SrTiO3[100]//Si[110]. The minimum yield of the Rutherford backscattering ion channeling in MgxZn1−xO layer was only 4%, indicating good crystalline quality of the film. Smooth surface morphology with rms roughness of 0.6 nm was observed using atomic force microscopy. Photodetectors fabricated on Mg0.68Zn0.32O/SrTiO3/Si show peak photoresponse at 225 nm, which is in the deep UV region.
TL;DR: In this paper, the authors used microwave plasma chemical vapour deposition to grow epitaxial diamond layers with low boron doping, from 5 × 1014 to 1 × 1016 cm−3, and the compensating n-type impurities are the lowest reported for any semiconducting diamond, 700 °C for 1 s in air.
Abstract: Exceptionally pure epitaxial diamond layers have been grown by microwave plasma chemical vapour deposition, which have low boron doping, from 5 × 1014 to 1 × 1016 cm−3, and the compensating n-type impurities are the lowest reported for any semiconducting diamond, 700 °C for ~1 s in air. Schottky diodes made on these epitaxial diamond films have breakdown voltages >6 kV, twelve times the highest breakdown voltage reported for any diamond diode and higher than any other semiconductor Schottky diode.
Patent•
02 May 2003TL;DR: In this paper, a method of fabricating a gallium-nitride-based semiconductor structure on a substrate includes the steps of forming a mask having at least one opening therein directly on the substrate, growing a buffer layer through the opening, and growing a layer of gallium nitride upwardly from the buffer layer and laterally across the mask.
Abstract: A method of fabricating a gallium nitride-based semiconductor structure on a substrate includes the steps of forming a mask having at least one opening therein directly on the substrate, growing a buffer layer through the opening, and growing a layer of gallium nitride upwardly from the buffer layer and laterally across the mask. During growth of the gallium nitride from the mask, the vertical and horizontal growth rates of the gallium nitride layer are maintained at rates sufficient to prevent polycrystalline material nucleating on said mask from interrupting the lateral growth of the gallium nitride layer. In an alternative embodiment, the method includes forming at least one raised portion defining adjacent trenches in the substrate and forming a mask on the substrate, the mask having at least one opening over the upper surface of the raised portion. A buffer layer may be grown from the upper surface of the raised portion. The gallium nitride layer is then grown laterally by pendeoepitaxy over the trenches.
TL;DR: In this article, structural and optical properties of Zn1−xCdxO layers grown by metalorganic vapor phase epitaxy were analyzed, and a narrowing of the fundamental band gap of up to 300 meV was observed.
Abstract: The development of ZnO-based semiconductor devices requires band gap engineering. Ternary Zn1−xCdxO allows reduction of the band gap relative to ZnO, which would be necessary for devices emitting visible light. We have analyzed the structural and optical properties of Zn1−xCdxO layers grown by metalorganic vapor-phase epitaxy. A narrowing of the fundamental band gap of up to 300 meV has been observed, while introducing a lattice mismatch of only 0.5% with respect to binary ZnO. Photoluminescence, high-resolution x-ray diffraction, and spatially resolved cathodoluminescence measurements revealed a lateral distribution of two different cadmium concentrations within the Zn1−xCdxO layers.
TL;DR: In this article, the role of ZnO as epitaxial initiator layer for the growth mechanism is clarified, while the ratio of the thickness of both layers controls the film composition.
Abstract: Single-crystalline thin films of the homologous series InGaO3(ZnO)m (where m is an integer) are fabricated by the reactive solid-phase epitaxy (R-SPE) method. Specifically, the role of ZnO as epitaxial initiator layer for the growth mechanism is clarified. High-temperature annealing of bilayer films consisting of an amorphous InGaO3(ZnO)5 layer deposited at room temperature and an epitaxial ZnO layer on yttria-stabilized zirconia (YSZ) substrate allows for the growth of single-crystalline film with controlled chemical composition. The epitaxial ZnO thin layer plays an essential role in determining the crystallographic orientation, while the ratio of the thickness of both layers controls the film composition.
26 Mar 2003
TL;DR: In this article, the authors presented a topological analysis of defects in Nitride Semiconductors and showed that the defects in Wurtzite GaN layers can be traced back to GaN-based Epitaxial Lateral Overgrowth of GaN.
Abstract: Preface.List of Contributors.PART 1: MATERIAL.1. High-Pressure Crystallization of GaN (I. Grzegory, et al.).2. Epitaxial Lateral Overgrowth of GaN (P. Gibart, et al.).3. Plasma-Assisted Molecular Beam Epitaxy of III-V Nitrides (A. Georgakilas, et al.).4. Growth of Gallium Nitride by Hydride Vapor Phase Epitaxy (A. Trassoudaine, et al.).5. Growth and Properties of InN (V. Davydov, et al.).6. Surface Structure and Adatom Kinetics of Group-III Nitrides (J. Neugebauer).PART 2: DEFECTS AND INTERFACES.7. Topological Analysis of Defects in Nitride Semiconductors (G. Dimitrakopulos, et al.).8. Extended Defects in Wurtzite GaN Layers: Atomic Structure, Formation, and Interaction Mechanisms (P. Ruterana, et al.).9. Stain, Chemical Composition, and Defects Analysis at Atomic Level in GaN-based Epitaxial Layers (S. Kret, et al.).PART 3: PROCESSING AND DEVICES.10. Ohmic Contacts to GaN (P. Hartlieb, et al.). 11. Electroluminescent Diodes and Laser Diodes (H. Amano).12. GaN-Based Modulation-Doped FETs and Heterojunction Bipolar Transistors ( H. Morkoc & L. Liu).13. GaN-Based UV Photodetectors (F. Omnes & E. Monroy).Subject Index.
TL;DR: In this article, an in situ method for the determination of the stress in GaN layers on hetero-substrates, in particular Si, via measuring the wafer curvature is presented.
Abstract: We present an in situ method for the determination of the stress in GaN layers on hetero-substrates, in particular Si, via measuring the wafer curvature. For device application it is essential to obtain stress free low-curvature layers. With our in situ method we directly observe the evolution of strain and can identify the sources of strain and the efficiency of strain compensating layers. We find a strong increase in tensile stress with increasing Si doping up to 0.18 GPa for a 1018 cm−3 Si doping concentration. This can be significantly reduced by an appropriate buffer layer growth scheme. The compensation of tensile thermal stress by introducing AlN interlayers to avoid cracking of GaN on Si is in situ investigated. We find that the impact of undoped AlN interlayers is independent of growth temperatures Tgrowth up to Tgrowth > 1000 °C. A linear dependence of strain reduction on AlN interlayer thickness up to a thickness of 12 nm is observed. Using appropriate growth schemes more than 6 μm thick crack free high quality GaN layers on Si were grown. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Patent•
20 Mar 2003
TL;DR: In this article, a GaN compound semiconductor having a greatly reduced number of dislocations is obtained in lateral growth regions (regions A where the substrate 1 is exposed), where the GaN layer grows epitaxially and threedimensionally (not only in a vertical direction but also in a lateral direction) on the Al0.15Ga0.85N layer 2.
Abstract: An Al0.15Ga0.85N layer 2 is formed on a silicon substrate 1 in a striped or grid pattern. A GaN layer 3 is formed in regions A where the substrate 1 is exposed and in regions B which are defined above the layer 2. At this time, the GaN layer grows epitaxially and three-dimensionally (not only in a vertical direction but also in a lateral direction) on the Al0.15Ga0.85N layer 2. Since the GaN layer grows epitaxially in the lateral direction as well, a GaN compound semiconductor having a greatly reduced number of dislocations is obtained in lateral growth regions (regions A where the substrate 1 is exposed).
TL;DR: In this article, a step growth method was proposed to suppress the oxidation of the substrate surface and thereby achieve oxide films with a high degree of crystallinity, and the epitaxy of high-quality SrTiO3 (STO) thin films directly on Si was achieved.
Abstract: Most semiconductor materials such as Si, Ge, and GaAs are subject to oxidation when exposed to oxidants. This results in difficulties in the heterointegration of epitaxial oxides on these semiconductors. Even though certain oxides may be thermodynamically stable when placed in contact with semiconductors, direct epitaxy of these oxides encounters kinetic difficulties due to the loss of epitaxy caused by the formation of an amorphous oxide at the interface. In this article, we address some important issues on the heteroepitaxy of oxides on semiconductors and show a stepped growth method that utilizes the kinetic characteristics of the growth process to suppress the oxidation of the substrate surface and thereby achieve oxide films with a high degree of crystallinity. The epitaxy of high-quality SrTiO3 (STO) thin films directly on Si was achieved. The chemical and structural properties of the STO/Si interface were evaluated in situ using reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy, and ex situ using transmission electron microscopy and electron energy loss spectroscopy.
Patent•
19 Mar 2003TL;DR: In this paper, a delta doping method is described, including the steps of: depositing semiconductor material on a substrate by a first epitaxial film growth process, terminating the deposition of semiconductor materials on the substrate to present an epitaxia film surface, delta doping the semiconductor surface, to form a delta doped layer thereon.
Abstract: A Group III-V nitride microelectronic device structure including a delta doped layer (24) and/or a doped superlattice. A delta doping method is described, including the steps of: depositing semiconductor material on a substrate by a first epitaxial film growth process; terminating the deposition of semiconductor material on the substrate to present an epitaxial film surface; delta doping the semiconductor material at the epitaxial film surface, to form a delta doping layer thereon; terminating the delta doping; resuming deposition of semiconductor material to deposit semiconductor material on the delta doping layer, in a second epitaxial film growth process; and continuing the semiconductor material second epitaxial film growth process to a predetermined extent, to form a doped microelectronic device structure, wherein the delta doping layer (24) is internalized in semiconductor material deposited in the first and second epitaxial film growth processes.
TL;DR: In this article, structural and morphological characteristics of planar, nonpolar (1120) a-plane GaN films grown on (1102) r-plane sapphire by hydride vapor phase epitaxy were discussed.
Abstract: This letter discusses the structural and morphological characteristics of planar, nonpolar (1120) a-plane GaN films grown on (1102) r-plane sapphire by hydride vapor phase epitaxy. Specular films with thicknesses over 50 μm were grown, eliminating the severely faceted surfaces that have previously been observed for hydride vapor phase epitaxy-grown a-plane films. Internal cracks and crack healing, similar to that in c-plane GaN films, were observed. Atomic force microscopy revealed nanometer-scale pitting and steps on the film surfaces, with rms roughness of ∼2 nm. X-ray diffraction confirmed the films are solely a-plane oriented with on-axis (1120) and 30° off-axis (1010) rocking curve peak widths of 1040 and 3000 arcsec, respectively. Transmission electron microscopy revealed a typical basal plane stacking fault density of 4×105 cm−1. The dislocation content of the films consisted of predominately edge component (bedge=±[0001]) threading dislocations with a density of 2×1010 cm−2, and mixed-characte...
TL;DR: In this paper, a single crystalline metal oxide nanowire was constructed using indium-doped tin oxide (In−SnO2) during a heteroepitaxial growth process.
Abstract: In this report, we show controlled in-situ doping of a single crystalline metal oxide nanowire, using indium-doped tin oxide (In−SnO2) as an example, during a heteroepitaxial growth process. Highly regular and high-density arrays of In−SnO2 nanowires, which demonstrate three- and four-fold growth symmetry, are obtained directly on optical sapphire substrates. Similar synthesis strategies, involving careful selection of desired growth conditions and smart manipulation of favorable thermodynamic properties, could be extended to production of various doped metal oxide nanowires.
TL;DR: In this paper, a thin InGaN epilayer is grown on a GaN buffer layer and then annealed at the growth temperature in molecular nitrogen inducing quantum dot formation, which reveals sharp peaks with typical linewidths of ∼700μeV at 4.2 K.
Abstract: We describe the growth of InGaN quantum dots (QDs) by metalorganic vapor phase epitaxy. A thin InGaN epilayer is grown on a GaN buffer layer and then annealed at the growth temperature in molecular nitrogen inducing quantum dot formation. Microphotoluminescence studies of these QDs reveal sharp peaks with typical linewidths of ∼700 μeV at 4.2 K, the linewidth being limited by the spectral resolution. Time-resolved photoluminescence suggests that the excitons in these structures have lifetimes in excess of 2 ns at 4.2 K.
TL;DR: In this article, the electrical activity of nitrogen acceptor in ZnO has been investigated in two ways: nitrogen was introduced by means of diallylamine during metalorganic vapor phase epitaxy (MOVPE) yielding incorporation of nitrogen in the range 1016-1021 cm−3.
Abstract: The electrical activity of nitrogen as an acceptor in ZnO has been investigated in two ways. First, nitrogen was introduced by means of diallylamine during metalorganic vapor phase epitaxy (MOVPE) yielding incorporation of nitrogen in the range 1016–1021 cm−3. This led to significant compensation of the natural donors with a minimum electron concentration of 5×1014 cm−3. Second, diffusion of nitrogen was carried out on undoped MOVPE layers under high pressure conditions stemming from the decomposition of NH4NO3. Conversion to p-type conductivity was observed in a systematic way with measured hole concentrations up to 6.5×1017 cm−3.
TL;DR: SrTiO3 thin films were prepared from Sr(thd)2 (thd ¼ 2,2,6,6-tetramethyl-3,5-heptanedionate) and titanium isopropoxide (Ti(O-i-Pr)4) on Si(1 0 0) substrates by atomic layer deposition (ALD) followed by rapid thermal annealing as discussed by the authors.
TL;DR: In this paper, high-oriented Ga-doped ZnO nanorod arrays have been fabricated on GaN and sapphire substrates by pulsed laser deposition and X-ray diffraction shows that these nanorods are grown epitaxially with the c-axis normal to the substrate.
Abstract: Highly oriented Ga-doped ZnO nanorod arrays have been fabricated on GaN and sapphire substrates by pulsed laser deposition. X-ray diffraction shows that these nanorods are grown epitaxially with the c-axis normal to the substrate. The ZnO nanorod formation proceeds as follows. After a wetting layer of ZnO film grows to approximately 14 nm in thickness, the Stranski–Krastanov instability takes place due to interface strain. As a result, ZnO nanodots are formed uniformly on the ZnO layer. These nanodots then serve as nucleation sites for the subsequent electric-field-assisted growth of nanorods. Ga-doping level plays a key role in the formation of ZnO nanorods, while the oxygen partial pressure and the substrate temperature also affect the morphology of nanorods. These self-assembled and ordered ZnO nanorod arrays may be used in field emission and optoelectronic applications.
TL;DR: The magnetic and transport properties of theEpitaxial synthesis and properties of novel Co and Mn-doped Ge magnetic semiconductors exhibit high T(C) and large magnetoresistance effects that can be controlled systematically by the doping concentration.
Abstract: Epitaxial synthesis and properties of novel Co and Mn-doped Ge magnetic semiconductors were studied. Epitaxial growth of high quality films with high doping concentrations has been stabilized by the use of two dopants. The magnetic and transport properties of the system exhibit high T(C) and large magnetoresistance effects that can be controlled systematically by the doping concentration. The maximum T(C) achieved in the semiconducting materials is approximately 270 K at a composition of Co0.12Mn0.03Ge0.85.
TL;DR: In this article, an optimized growth temperature range was established, where ferromagnetic Fe3Si/GaAs(001) hybrid structures with high crystalline and interfacial quality can be fabricated by molecular-beam epitaxy.
Abstract: We have established an optimized growth temperature range, namely, 150 °C
TL;DR: It is demonstrated that heteroepitaxial c-BN films can be prepared at 900 °C on highly (001)-oriented diamond films, formed by chemical vapour deposition, using ion-beam-assisted deposition as a low-pressure technique.
Abstract: Cubic boron nitride (c-BN), although offering a number of highly attractive properties comparable to diamond, like hardness, chemical inertness and a large electronic bandgap, up to now has not found the attention it deserves. This mostly has to do with preparational problems, with easy chemical routes not available and, instead, the necessity to apply ion-bombardment-assisted methods. Hence, most of the c-BN samples prepared as thin films have been nanocrystalline, making the prospect of using this material for high-temperature electronic applications an illusion. Although heteroepitaxial nucleation of c-BN on diamond substrates has been demonstrated using the high-pressure-high-temperature technique, none of the low-pressure methods ever succeeded in the epitaxial growth of c-BN on any substrate. Here, we demonstrate that heteroepitaxial c-BN films can be prepared at 900 degrees C on highly (001)-oriented diamond films, formed by chemical vapour deposition, using ion-beam-assisted deposition as a low-pressure technique. The orientation relationship was found to be c-BN(001)[100]||diamond(001)[100]. High-resolution transmission electron microscopy additionally proved that epitaxy can be achieved without an intermediate hexagonal BN layer that is commonly observed on various substrates.
TL;DR: In this article, a hexagonal, single crystal GaN along the c-axis was grown on Si (111) surface through self-assembly by molecular-beam epitaxy.
Abstract: Dislocation-free vertical GaN pillars in nanoscale were grown on Si (111) surface through self-assembly by molecular-beam epitaxy. No extra catalytic or nanostructural assistance has been employed. These nanorods have a lateral dimension from ≲10 nm to ∼800 nm and a height of ≲50 nm to ≳3 μm protruding above the film, depending on the growth parameters. The top view of the nanorods has a hexagonal shape from scanning electron microscopy. Transmission electron microscopy shows that the nanorods are hexagonal, single crystal GaN along the c-axis. An extra peak at 363 nm originated from nanorods was observed in photoluminescence spectra at 66 K, which is ascribed to the surface states according to the results of surface passivation. Micro-Raman spectroscopy on a single nanorod reveals E1 and E2 modes at 559.0 and 567.4 cm−1, respectively. Large strain was observed in both the transmission electron micrograph and the Raman shift. A possible growth mechanism is discussed.