Showing papers on "Epitaxy published in 2013"
TL;DR: The epitaxial growth of single-domain graphene on h-BN by a plasma-assisted deposition method and the synthesis method is potentially applicable on other flat surfaces could open new ways of graphene band engineering through epitaxy on different substrates.
Abstract: The epitaxial growth of large-area single-domain graphene on hexagonal boron nitride by plasma-assisted deposition is now reported. New sets of Dirac points are produced as a result of a trigonal superlattice potential, while Dirac fermion physics near the original Dirac point remain unperturbed. This growth approach could enable band engineering in graphene through epitaxy on different substrates.
870 citations
TL;DR: This study has successfully grown predominantly monolayer MoS2 on an inert and nearly lattice-matching mica substrate by using a low-pressure chemical vapor deposition method, and the homogeneously strained high-quality monolayers prepared in this study could competitively be exploited for a variety of future applications.
Abstract: Molybdenum disulfide (MoS2) is back in the spotlight because of the indirect-to-direct bandgap tunability and valley related physics emerging in the monolayer regime. However, rigorous control of the monolayer thickness is still a huge challenge for commonly utilized physical exfoliation and chemical synthesis methods. Herein, we have successfully grown predominantly monolayer MoS2 on an inert and nearly lattice-matching mica substrate by using a low-pressure chemical vapor deposition method. The growth is proposed to be mediated by an epitaxial mechanism, and the epitaxial monolayer MoS2 is intrinsically strained on mica due to a small adlayer-substrate lattice mismatch (∼2.7%). Photoluminescence (PL) measurements indicate strong single-exciton emission in as-grown MoS2 and room-temperature PL helicity (circular polarization ∼0.35) on transferred samples, providing straightforward proof of the high quality of the prepared monolayer crystals. The homogeneously strained high-quality monolayer MoS2 prepared...
510 citations
TL;DR: In this paper, a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN was shown to have a reduced energy bandgap for hexagonal AlN.
Abstract: Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.
239 citations
TL;DR: In this paper, Schottky barrier diodes and metal-semiconductor field effect transistors (MESFETs) were demonstrated for the first time on β-Ga2O3 homoepitaxial layers.
235 citations
IBM1
TL;DR: This work presents an epitaxial lift-off scheme that minimizes the amount of post-etching residues and keeps the surface smooth, leading to direct reuse of the gallium arsenide substrate, enabling direct substrate reuse by solar cells grown on the original and the reused substrates.
Abstract: Epitaxial lift-off process enables the separation of III-V device layers from gallium arsenide substrates and has been extensively explored to avoid the high cost of III-V devices by reusing the substrates. Conventional epitaxial lift-off processes require several post-processing steps to restore the substrate to an epi-ready condition. Here we present an epitaxial lift-off scheme that minimizes the amount of post-etching residues and keeps the surface smooth, leading to direct reuse of the gallium arsenide substrate. The successful direct substrate reuse is confirmed by the performance comparison of solar cells grown on the original and the reused substrates. Following the features of our epitaxial lift-off process, a high-throughput technique called surface tension-assisted epitaxial lift-off was developed. In addition to showing full wafer gallium arsenide thin film transfer onto both rigid and flexible substrates, we also demonstrate devices, including light-emitting diode and metal-oxide-semiconductor capacitor, first built on thin active layers and then transferred to secondary substrates.
234 citations
TL;DR: Current approaches for the preparation of modified pristine graphene are reviewed, which encompass the use of graphite as initial material and are directed to wet chemical approaches toward high-quality graphene flakes.
217 citations
TL;DR: Ferroelectric switching of 8- to 40-nm-thick BaTiO₃ films in metal-ferroelectric-semiconductor structures is realized, and field-effect devices using this epitaxial oxide stack can be envisaged.
Abstract: Epitaxial growth of SrTiO₃ on silicon by molecular beam epitaxy has opened up the route to the integration of functional complex oxides on a silicon platform. Chief among them is ferroelectric functionality using perovskite oxides such as BaTiO₃. However, it has remained a challenge to achieve ferroelectricity in epitaxial BaTiO₃ films with a polarization pointing perpendicular to the silicon substrate without a conducting bottom electrode. Here, we demonstrate ferroelectricity in such stacks. Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal the presence of crystalline domains with the long axis of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and are reversibly switched with a phase change of 180°. Open, saturated hysteresis loops are recorded. Thus, ferroelectric switching of 8- to 40-nm-thick BaTiO₃ films in metal-ferroelectric-semiconductor structures is realized, and field-effect devices using this epitaxial oxide stack can be envisaged.
211 citations
TL;DR: In this paper, the photoelectrochemical performances of Ti-doped and undoped hematite electrodes were examined and compared under water oxidation conditions, and the incorporation of Ti atoms into hematitic electrodes was found to dramatically enhance the water oxidation performance with much greater enhancement found for the thinnest films.
Abstract: Uniform thin films of hematite and Ti-doped hematite (α-Fe2O3) were deposited on transparent conductive substrates using atomic layer deposition (ALD). ALD's epitaxial growth mechanism allowed the control of the morphology and thickness of the hematite films as well as the concentration and distribution of Ti atoms. The photoelectrochemical performances of Ti-doped and undoped hematite electrodes were examined and compared under water oxidation conditions. The incorporation of Ti atoms into hematite electrodes was found to dramatically enhance the water oxidation performance, with much greater enhancement found for the thinnest films. An optimum concentration ∼3 atomic% of Ti atoms was also determined. A series of electrochemical, photoelectrochemical and impedance spectroscopy measurements were employed to elucidate the cause of the improved photoactivity of the Ti-doped hematite thin films. This performance enhancement was a combination of improved bulk properties (hole collection length) and surface properties (water oxidation efficiency). The improvement in both bulk and surface properties is attributed to the resurrection of a dead layer by the Ti dopant atoms.
209 citations
TL;DR: Density functional theory calculations reveal that the binding between graphene and sapphire is dominated by weak dispersion interactions and indicate that the epitaxial relation as observed by GIXRD is due to preferential binding of small molecules on sappire during early stages of graphene formation.
Abstract: van der Waals epitaxial growth of graphene on c-plane (0001) sapphire by CVD without a metal catalyst is presented. The effects of CH4 partial pressure, growth temperature, and H2/CH4 ratio were investigated and growth conditions optimized. The formation of monolayer graphene was shown by Raman spectroscopy, optical transmission, grazing incidence X-ray diffraction (GIXRD), and low voltage transmission electron microscopy (LVTEM). Electrical analysis revealed that a room temperature Hall mobility above 2000 cm2/V·s was achieved, and the mobility and carrier type were correlated to growth conditions. Both GIXRD and LVTEM studies confirm a dominant crystal orientation (principally graphene [10–10] || sapphire [11–20]) for about 80–90% of the material concomitant with epitaxial growth. The initial phase of the nucleation and the lateral growth from the nucleation seeds were observed using atomic force microscopy. The initial nuclei density was ∼24 μm–2, and a lateral growth rate of ∼82 nm/min was determined....
207 citations
TL;DR: It is demonstrated that the embedded graphene oxide in a gallium nitride light-emitting diode alleviates the self-heating issues by virtue of its heat-spreading ability and reducing the thermal boundary resistance.
Abstract: The future of solid-state lighting relies on how the performance parameters will be improved further for developing high-brightness light-emitting diodes. Eventually, heat removal is becoming a crucial issue because the requirement of high brightness necessitates high-operating current densities that would trigger more joule heating. Here we demonstrate that the embedded graphene oxide in a gallium nitride light-emitting diode alleviates the self-heating issues by virtue of its heat-spreading ability and reducing the thermal boundary resistance. The fabrication process involves the generation of scalable graphene oxide microscale patterns on a sapphire substrate, followed by its thermal reduction and epitaxial lateral overgrowth of gallium nitride in a metal-organic chemical vapour deposition system under one-step process. The device with embedded graphene oxide outperforms its conventional counterpart by emitting bright light with relatively low-junction temperature and thermal resistance. This facile strategy may enable integration of large-scale graphene into practical devices for effective heat removal.
194 citations
TL;DR: The impact of post-deposition hydrogen plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated in this paper.
Abstract: The impact of post-deposition hydrogen plasma treatment (HPT) on passivation in amorphous/crystalline silicon (a-Si:H/c-Si) interfaces is investigated. Combining low temperature a-Si:H deposition and successive HPT, a high minority carrier lifetime >8 ms is achieved on c-Si 〈100〉, which is otherwise prone to epitaxial growth and thus inferior passivation. It is shown that the passivation improvement stems from diffusion of hydrogen atoms to the heterointerface and subsequent dangling bond passivation. Concomitantly, the a-Si:H hydrogen density increases, leading to band gap widening and void formation, while the film disorder is not increased. Thus, HPT allows for a-Si:H band gap and a-Si:H/c-Si band offset engineering.
TL;DR: The role of the oxygen vacancies on the phase transition behavior of this VO2 film is discussed in the framework of the hybridization theory and the valence state of vanadium in this paper.
Abstract: VO2 epitaxial film with large size has been prepared by oxide-molecular beam epitaxy method on Al2O3 (0001) substrate. The VO2 film shows a perfect crystal orientation, uniformity, and distinct metal-insulator phase transition (MIT) characteristics. It is observed that the MIT character is closely associated with the crystal defects such as oxygen vacancies. By controlling the growth condition, the MIT temperature can be tuned through modifying the content of oxygen vacancies. The role of the oxygen vacancies on the phase transition behavior of this VO2 film is discussed in the framework of the hybridization theory and the valence state of vanadium.
TL;DR: Flexoelectricity can play an important role in the reversal of the self-polarization direction in epitaxial BiFeO3 thin films.
Abstract: Flexoelectricity can play an important role in the reversal of the self-polarization direction in epitaxial BiFeO3 thin films. The flexoelectric and interfacial effects compete with each other to determine the self-polarization state. In Region I, the self-polarization is downward because the interfacial effect is more dominant than the flexoelectric effect. In Region II, the self-polarization is upward, because the flexoelectric effect becomes more dominant than the interfacial effect.
TL;DR: The combination of strained- NM-compatible doping techniques with self-sustained-strain sharing by applying a strain-sharing scheme between Si and SiGe multiple epitaxial layers, to create strained print-transferrable SiNMs are demonstrated.
Abstract: Fast flexible electronics operating at radio frequencies (>1 GHz) are more attractive than traditional flexible electronics because of their versatile capabilities, dramatic power savings when operating at reduced speed and broader spectrum of applications. Transferrable single-crystalline Si nanomembranes (SiNMs) are preferred to other materials for flexible electronics owing to their unique advantages. Further improvement of Si-based device speed implies significant technical and economic advantages. While the mobility of bulk Si can be enhanced using strain techniques, implementing these techniques into transferrable single-crystalline SiNMs has been challenging and not demonstrated. The past approach presents severe challenges to achieve effective doping and desired material topology. Here we demonstrate the combination of strained- NM-compatible doping techniques with self-sustained-strain sharing by applying a strain-sharing scheme between Si and SiGe multiple epitaxial layers, to create strained print-transferrable SiNMs. We demonstrate a new speed record of Si-based flexible electronics without using aggressively scaled critical device dimensions.
TL;DR: In this article, the reliability and output power of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) fabricated on AlN substrates prepared by hydride vapor phase epitaxy are reported.
Abstract: The reliability and output power of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) fabricated on AlN substrates prepared by hydride vapor phase epitaxy are reported. TEM analysis revealed that dislocation density in LED layers, except the p-GaN layer, was below 106 cm-2. DUV-LEDs emitting at 261 nm exhibited an output power of 10.8 mW at 150 mA. The lifetime of these LEDs was estimated to be over 10,000 h for cw operation at 50 mA. No significant acceleration of output power decay at higher operation currents was observed. The estimated lifetime at the operation current of 150 mA was over 5,000 h.
TL;DR: In this paper, the authors used low-energy electron microscopy (LEEM) to study the structure, initial growth orientation, growth progression, and the number of layers of atomically thin hexagonal boron nitride (h-BN) films.
Abstract: Low-energy electron microscopy (LEEM) has been used to study the structure, initial growth orientation, growth progression, and the number of layers of atomically thin hexagonal boron nitride (h-BN) films. The h-BN films are grown on heteroepitaxial Co using chemical vapor deposition (CVD) at low pressure. Our findings from LEEM studies include the growth of monolayer film having two, oppositely oriented, triangular BN domains commensurate with the Co lattice. The growth of h-BN appears to be self-limiting at a monolayer, with thicker domains only appearing in patches, presumably initiated between domain boundaries. Reflectivity measurements of the thicker h-BN films show oscillations resulting from the resonant electron transmission through quantized electronic states of the h-BN films, with the number of minima scaling up with the number of h-BN layers. First principles density functional theory (DFT) calculations show that the positions of oscillations are related to the electronic band structure of h-BN.
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TL;DR: Sp spontaneous phase segregation of InGaAs NWs on graphene results in spontaneous phase separation starting from the beginning of growth, yielding a well-defined InAs-In(x)Ga(1-x)As (0.2 < x < 1) core-shell structure.
Abstract: The growth of high-density arrays of vertically oriented, single crystalline InAs NWs on graphene surfaces are realized through the van der Waals (vdW) epitaxy mechanism by metalorganic chemical vapor deposition (MOCVD). However, the growth of InGaAs NWs on graphene results in spontaneous phase separation starting from the beginning of growth, yielding a well- defined InAs−InxGa1−xAs (0.2 < x < 1) core−shell structure. The core−shell structure then terminates abruptly after about 2 μ mi n height, and axial growth of uniform composition InxGa1−xAs takes place without a change in the NW diameter. The InxGa1−xAs shell composition changes as a function of indium flow, but the core and shell thicknesses and the onset of nonsegregated InxGa1−xAs axial segment are independent of indium composition. In contrast, no InGaAs phase segregation has been observed when growing on MoS2, another two-dimensional (2D) layered material, or via the Au-assisted vapor−liquid−solid (VLS) mechanism on graphene. This spontaneous phase segregation phenomenon is elucidated as a special case of van der Waals epitaxy on 2D sheets. Considering the near lattice matched registry between InAs and graphene, InGaAs is forced to self-organize into InAs core and InGaAs shell segments since the lack of dangling bonds on graphene does not allow strain sharing through elastic deformation between InGaAs and graphene.
TL;DR: In this paper, cobalt oxide (CoO) films are grown epitaxially on Si(001) by atomic layer deposition (ALD) using a thin buffer layer of strontium titanate (STO) grown by molecular beam epitaxy.
Abstract: Cobalt oxide (CoO) films are grown epitaxially on Si(001) by atomic layer deposition (ALD) using a thin (1.6 nm) buffer layer of strontium titanate (STO) grown by molecular beam epitaxy. The ALD growth of CoO films is done at low temperature (170–180 °C), using cobalt bis(diisopropylacetamidinate) and water as co-reactants. Reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional scanning transmission electron microscopy are performed to characterize the crystalline structure of the films. The CoO films are found to be crystalline as-deposited even at the low growth temperature with no evidence of Co diffusion into Si. The STO-buffered Si (001) is used as a template for ALD growth of relatively thicker epitaxial STO and TiO2 films. Epitaxial and polycrystalline CoO films are then grown by ALD on the STO and TiO2 layers, respectively, creating thin-film heterostructures for photoelectrochemical testing. Both types of heterostructures, CoO/STO/Si and CoO/TiO2/STO/Si, demonstrate water photooxidation activity under visible light illumination. In-situ X-ray photoelectron spectroscopy is used to measure the band alignment of the two heterojunctions, CoO/STO and CoO/TiO2. The experimental band alignment is compared to electronic structure calculations using density functional theory.
TL;DR: In this article, Hall effect and capacitancevoltage measurements were performed on p-type GaN:Mg layers grown on GaN templates by molecular beam epitaxy with a high range of Mg-doping concentrations.
Abstract: Hall effect and capacitance-voltage C(V) measurements were performed on p-type GaN:Mg layers grown on GaN templates by molecular beam epitaxy with a high range of Mg-doping concentrations. The free hole density and the effective dopant concentration NA−ND as a function of magnesium incorporation measured by secondary ion mass spectroscopy clearly reveal both a magnesium doping efficiency up to 90% and a strong dependence of the acceptor ionization energy Ea with the acceptor concentration NA. These experimental observations highlight an isolated acceptor binding energy of 245±25 meV compatible, at high acceptor concentration, with the achievement of p-type GaN:Mg layers with a hole concentration at room temperature close to 1019 cm−3.
TL;DR: Highly-oriented ZIF-8 thin films with controllable thickness were grown on an -OH-functionalized Au substrate using the liquid phase epitaxy method at room temperature, as evidenced by SEM and PXRD.
TL;DR: Using low-temperature scanning tunneling microscopy, it is shown that monolayer hexagonal boron nitride (h-BN) on Ir(111) acts as ultrathin insulating layer for organic molecules, while simultaneously templating their self-assembly.
Abstract: Using low-temperature scanning tunneling microscopy, we show that monolayer hexagonal boron nitride (h-BN) on Ir(111) acts as ultrathin insulating layer for organic molecules, while simultaneously templating their self-assembly. Tunneling spectroscopy experiments on cobalt phthalocyanine (CoPC) reveal narrow molecular resonances and indicate that the charge state of CoPC is periodically modulated by the h-BN moire superstructure. Molecules in the second layer show site-selective adsorption behavior, allowing the synthesis of molecular dimers that are spatially ordered and inaccessible by usual chemical means.
TL;DR: In this article, single crystal epitaxial Ge1−xSnx alloys with atomic fractions of tin up to x ǫ = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates.
Abstract: Single crystal epitaxial Ge1−xSnx alloys with atomic fractions of tin up to x = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates. The Ge1−xSnx alloys formed high quality, coherent, strained layers at growth temperatures below 250 °C, as shown by high resolution X-ray diffraction. The amount of Sn that was on lattice sites, as determined by Rutherford backscattering spectrometry channeling, was found to be above 90% substitutional in all alloys. The degree of strain and the dependence of the effective unstrained bulk lattice constant of Ge1−xSnx alloys versus the composition of Sn have been determined.
TL;DR: In this paper, the defect structure and homogeneity of 1-3-µm thick AlxGa1−xN layers grown on epitaxially laterally overgrown (ELO) AlN on patterned AlN/sapphire templates have been investigated in dependence on the miscut direction of the c-plane sapphire substrates, the etching depth into the SA and the Al concentration.
TL;DR: In this article, Si-doped Al0.6Ga0.4N films were studied using deep ultraviolet timeresolved photoluminescence and time-resolved cathodolumininescence spectroscopies.
Abstract: Luminescence dynamics for the near-band-edge (NBE) emission peak at around 250 nm of c-plane Si-doped Al0.6Ga0.4N films grown on AlN templates by low-pressure metalorganic vapor phase epitaxy were studied using deep ultraviolet time-resolved photoluminescence and time-resolved cathodoluminescence spectroscopies. For the films with the Si-doping concentration, [Si], lower than 1.9 × 1017 cm–3, the doping lessened the concentration of cation vacancies, [VIII], through the surfactant effect or the aid of the reactant doping in a form of H3SiNH2. However, the room-temperature nonradiative lifetime, and, consequently, the equivalent value of internal quantum efficiency in the weak excitation regime steeply decreased when [Si] exceeded 1018 cm−3. Simultaneously, the intensity ratio of the deep-state emission band to the NBE emission abruptly increased. Because the increase in [Si] essentially gives rise to the increase in [VIII] (for [Si]>1.9×1017 cm−3) and the overcompensation of Si is eventually observed for ...
TL;DR: Un unreported experimental evidence is presented of a four-stage hierarchical development of octahedral-framework perturbations resulting from a progressive imbalance between electronic, elastic, andOctahedral tilting energies in La(0.7)Sr( 0.3)MnO( 3) epitaxial thin films grown on SrTiO(3) substrates.
Abstract: Strain engineering of functional properties in epitaxial thin films of strongly correlated oxides exhibiting octahedral-framework structures is hindered by the lack of adequate misfit relaxation models. Here we present unreported experimental evidence of a four-stage hierarchical development of octahedral-framework perturbations resulting from a progressive imbalance between electronic, elastic, and octahedral tilting energies in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ epitaxial thin films grown on ${\mathrm{SrTiO}}_{3}$ substrates. Electronic softening of the Mn-O bonds near the substrate leads to the formation of an interfacial layer clamped to the substrate with strongly degraded magnetotransport properties, i.e., the so-called dead layer, while rigid octahedral tilts become relevant at advanced growth stages without significant effects on charge transport and magnetic ordering.
TL;DR: In this paper, large hexagonal single-crystalline domains of single-layer graphene are epitaxially grown by ambient-pressure chemical vapor deposition over a thin Cu(111) film deposited on c-plane sapphire.
Abstract: Large hexagonal single-crystalline domains of single-layer graphene are epitaxially grown by ambient-pressure chemical vapor deposition over a thin Cu(111) film deposited on c-plane sapphire. The hexagonal graphene domains with a maximum size of 100 µm are oriented in the same direction due to the epitaxial growth. Reflecting high crystallinity, a clear band structure with the Dirac cone is observed by angle-resolved photoelectron spectroscopy (ARPES), and a high carrier mobility exceeding 4,000 cm2 V-1 s-1 is obtained on SiO2/Si at room temperature. Our epitaxial approach combined with large domain growth is expected to contribute to future electronic applications.
TL;DR: In this article, the effects of SiH4/III ratio and aluminum content on the resistivity, the carrier concentration, and the mobility of AlGaN:Si layers were investigated.
Abstract: Silicon doping of AlxGa1−xN layers with high aluminum mole fractions (0.8 < x < 1) was studied. The AlGaN:Si layers were pseudomorphically grown by metalorganic vapor phase epitaxy on low defect density epitaxially laterally overgrown AlN/sapphire templates. The effects of SiH4/III ratio and aluminum content on the resistivity, the carrier concentration, and the mobility have been investigated. By variation of the SiH4/III ratio during the growth of AlxGa1−xN:Si layers, a recorded low resistivity of Al0.81Ga0.19N:Si was obtained with 0.026 Ω cm. The resistivity increases exponentially with increasing aluminum content to 3.35 Ω cm for Al0.96Ga0.04N, and the optimum SiH4/III ratio is shifted towards lower values. Hall effect measurements show that the increase of the resistivity with increasing aluminum mole fraction is mainly caused by a decrease of the carrier density. The optimized Al0.81Ga0.19N:Si exhibits a carrier concentration of 1.5 × 1019 cm−3 and a mobility of the carriers of 16.5 cm2 V−1 s−1.
TL;DR: In this paper, a new method is developed for the solid phase synthesis of epitaxial layers when the substrate itself is involved into a chemical reaction and the reaction product grows in the interior of substrate layer.
Abstract: A new method is developed for the solid-phase synthesis of epitaxial layers when the substrate itself is involved into a chemical reaction and the reaction product grows in the interior of substrate layer. It opens up new possibilities for the relaxation of the elastic energy due to attraction of point defects formed during the chemical reaction in anisotropic media. In the same time, the attracting point dilatation centers compose relatively stable formations—dilatation dipoles, named by analogy with electric dipoles, providing significant reduction of the total elastic energy. The correspondent theory of interaction of point dilatation centers in anisotropic crystals is developed. It is eliminated that the most advantageous location of the dipoles is the direction (111) in crystals with cubic symmetry. In order to confirm the theory, the single-crystal silicon carbide films with the thickness up to 200 nm have been grown on silicon (111) substrates owing to the chemical reaction with carbon monoxide. Grown high-quality single-crystal silicon carbide films do not contain misfit dislocations despite the huge lattice mismatch value of ∼20%. Also the possibility of growing of thick wide-gap semiconductor films on such templates SiC/Si(111) and, accordingly, its integration into silicon electronics, is demonstrated. In particular, a working LED structure based on gallium nitride has been produced. Finally, the thermodynamic theory of new phase nucleation due to a chemical reaction has been developed and it was shown that in the case under consideration the chemical equilibrium constant generalizes the concentration of adatoms exploited in a one-component nucleation theory.
TL;DR: Methods to grow high-quality gallium nitride (GaN) microdisks on amorphous silicon oxide layers formed on silicon using micropatterned graphene films as a nucleation layer are described.
Abstract: Direct epitaxial growth of inorganic compound semiconductors on lattice-matched single-crystal substrates has provided an important way to fabricate light sources for various applications including lighting, displays and optical communications. Nevertheless, unconventional substrates such as silicon, amorphous glass, plastics, and metals must be used for emerging optoelectronic applications, such as high-speed photonic circuitry and flexible displays. However, high-quality film growth requires good matching of lattice constants and thermal expansion coefficients between the film and the supporting substrate. This restricts monolithic fabrication of optoelectronic devices on unconventional substrates. Here, we describe methods to grow high-quality gallium nitride (GaN) microdisks on amorphous silicon oxide layers formed on silicon using micropatterned graphene films as a nucleation layer. Highly crystalline GaN microdisks having hexagonal facets were grown on graphene dots with intermediate ZnO nanowalls via epitaxial lateral overgrowth. Furthermore, whispering-gallery-mode lasing from the GaN microdisk with a Q-factor of 1200 was observed at room temperature.
TL;DR: Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy.
Abstract: Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy. Graded AlxGa1−xN and conventional Al0.7Ga0.3N layers grown on AlN are beryllium (Be) doped via epitaxial growth. The hole concentration in graded AlxGa1−xN:Be (x = 0.7 ∼ 1) layers demonstrates that polarization generates hole charges from Be dopant. The Al0.7Ga0.3N layer is not conductive owing to the absence of carriers generated from the Be dopant without the inducement of polarization. Polarization doping provides an approach to high efficiency p-type doping in high Al composition AlGaN.