3C-SiC Substrates Research Articles

Micro Raman and micro photoluminescence study of cubic GaN grown on 3C-SiC(0 0 1) substrates by metalorganic vapor phase epitaxy

We have investigated metalorganic vapor phase epitaxy-grown GaN grains on a 3C-SiC(0 0 1) substrate using micro Raman and micro photoluminescence spectroscopy. Polarized micro Raman spectra clearly showed that horizontal flat facets and inclined facets of the rectangular GaN grains correspond to cubic phase regions and hexagonal phase regions, respectively. To examine the photoluminescence properties of “pure” cubic GaN, micro photoluminescence was performed by focusing a laser beam on the horizontal flat facet. A strong photoluminescence line with the full-width at half-maximum of 5 meV was observed, which is the smallest value to date and shows that the crystal quality of the cubic phase region is excellent. We could clearly identify free exciton, donor bound exciton and acceptor bound exciton emissions in the cubic GaN.

Ferroelectric films prepared by laser ablation directly on SiC substrates

Because of the common physical properties of silicon carbide (SiC) and lead base ferroelectric films [such as lead zirconate titanate (PZT) and lead titanate (PTO)], it is interesting to investigate ferroelectrics and SiC based integrated devices for potential high radiation environments, high speed, high temperature, and high density memory applications. Here we first report our primary results of depositing lead base ferroelectric films directly onto bare SiC substrates. Ferroelectric films including undoped and doped PZT and PTO were directly deposited on bare 3C-SiC and 4H-SiC substrates. X-ray diffraction analyses indicate that all the PTO films deposited at substrate temperatures from 600 to 650 °C are polycrystalline of the pure perovskite phase. PZT films deposited at a substrate temperature of 570 °C are dominated by the pyrochlore phase and even at a higher substrate temperature of 650 °C both the perovskite and the pyrochlore phases coexist. The pyrochlore phase of the PZT films is able to be converted into the perovskite phase by rapid thermal annealing at 800 °C for 30–60 s. The formation of an interfacial layer of a nonferroelectric phase (Pb2Ti2O6), which is caused by interdiffusion, is one of the most serious problems during the fabrication of lead based ferroelectric films directly onto the Si wafer. However, there is no such interdiffusion observed between the ferroelectric films and the SiC substrates. Capacitance versus voltage (C–V) curves of metal/ferroelectric/semiconductor diode structures demonstrate typical C–V hysteresis loops and the capacitance versus temperature measurements further confirm the ferroelectric properties of the films.

Nickel film on (001) SiC: Thermally induced reactions

The reactions induced in a vacuum furnace (5×10 −7 Torr) between an electron-beam-evaporated Ni film a few hundred nm thick and a (001)-oriented (i.e. Si-face-oriented) single crystalline 3C–SiC substrate are investigated by 3.2 MeV 4He 2+ backscattering spectrometry, X-ray diffraction, secondary ion mass spectrometry, and scanning electron microscopy. Samples are characterized before and after annealing at temperatures of 400–700 oC for 30 min. At 450 oC, carbon diffuses throughout the Ni film and forms a carbon-rich layer at the Ni surface of a thickness of a few nm which remains unchanged during subsequent annealing. Some nickel silicides were detected at this initial stage but could not be clearly identified. At 450 oC (after 120 min) the Ni 31Si 12 phase starts to form. This is the only detected phase at 500 oC. The Ni 2Si phase, the silicide that is thermodynamically stable with SiC and carbon, forms first at the surface and grows toward the SiC substrate. At 600 oC, this reaction has consumed about half of the Ni 31Si 12 phase and at 700 oC, Ni 2Si is the only silicide in the reacted film. In all the reacted samples the carbon distribution is alike and consists of three distinct layers: a first zone with a constant carbon concentration that extends from near the SiC/silicide interface through most of the films thickness. The second zone is ∼70 nm thick and is deficient of carbon. The third zone is the thin graphite layer at the surface. There is oxygen in the film too, the distribution of which is related increasingly clearly to the carbon profile as the annealing temperature rises.

Investigation of luminescence properties of GaN single crystals grown on 3C-SiC substrates

Cathodoluminescence (CL) and photoluminescence (PL) investigations of single crystal GaN grown on 3C-SiC(100) substrates by metalorganic vapor-phase epitaxy are reported. The GaN grown on 3C-SiC substrates shows distinct crystal facets. We identified the square facet and inclined facet as cubic GaN and hexagonal GaN, respectively. We studied the luminescence properties from the square facet or from the inclined facets separately by CL. For the cubic GaN, a sharp excitonic transition and a weak DA pair transition were observed from the square facet. On the other hand, an emission line at 3.293eV was obtained from the inclined facets. By studying its temperature dependence, we suggest that the 3.293eV emission is due to the free electron to acceptor transition of hexagonal GaN.

Growth of cubic III-nitrides by gas source MBE using atomic nitrogen plasma: GaN, AlGaN and AlN

Cubic GaN, AlGaN and AlN epilayers were grown on 3C-SiC(001) substrates by gas source molecular beam epitaxy using radio-frequency N2 plasma containing atomic nitrogen species. Due to the enhancement of growth rate by this plasma source, cubic GaN epilayers with the thickness of several micrometers were obtained, and the quality of epilayers was so much improved that they showed an X-ray diffraction peak width as small as 9min. Cubic AlxGa1−xN and cubic AlN epilayers were also grown, and the variations of X-ray diffraction peak position and emission energy were observed according to the Al content.

Formation of Pyramidal Pits at the Interface of 3C-SiC and Si(001) Substrates Grown by Gas Source MBE

Formation of Pyramidal Pits at the Interface of 3C-SiC and Si(001) Substrates Grown by Gas Source MBE

Reaction of thin Ni films with (001) 3CSiC at 700°C

The reaction layer of a thermally reacted thin Ni film, deposited by electron-beam evaporation on a single crystalline (001) 3CSiC substrate, was investigated after vacuum annealing at 700°C in terms of its morphology and structure by cross-sectional transmission electron microscopy (TEM). Ni 2Si and carbon are identified as reaction products. Distinctive dissimilarities with depth in the morphology of the reacted layer are observed. Carbon appears to form isolated clusters in the upper part of the Ni 2Si layer and microcolumns in the lower part.

Crystal Structure of GaN Grown on 3C-SiC Substrates by Metalorganic Vapor Phase Epitaxy

GaN films were grown on 3C-SiC substrates by metalorganic vapor phase epitaxy (MOVPE) using 1,1-dimethylhydrazine (DMHy) as the N source. The crystal structure was strongly affected by both the growth temperature and the V/III ratio. At 600° C, only hexagonal GaN films with their c-axis perpendicular to the substrate surface were grown. At 800° C, relatively high V/III ratios resulted in the growth of hexagonal GaN with their c-axis oriented in the [111] direction while cubic GaN films were obtained at lower V/III ratios. The origin of [111]-oriented hexagonal GaN is also discussed.

Growth and characterization of cubic GaN

We have grown high-quality cubic GaN epilayers on GaAs and 3C-SiC substrates by molecular beam epitaxy technique using dimethylhydrazine or ammonia/nitrogen plasma as a nitrogen source. An X-ray diffraction peak width of 16 min and a low-temperature photoluminescence peak width of 19 meV were achieved. Various surface reconstruction transitions have been observed for cubic GaN(0 0 1) surfaces, recently. These results, along with previously published studies on cubic nitrides, are summarized, and the current status of the growth and characterization of cubic nitrides including AlN and InN is discussed.

Properties of PTO/YBCO Heterostructure on Bare SiC Substrates

ABSTRACTThe lead titanium oxide PbTiO3 (PTO) and High Tc Superconductor YBa2Cu3O7-x (YBCO) capacitor hetero structures have been fabricated by pulsed laser ablation directly on 3C-SiC substrates. X-ray diffraction analysis indicates that both PTO layer and YBCO layer are polycrystalline with a perovskite phase. The zero-field cooling (ZFC) curve of YBCO shows a transition temperature Tc around 60 K with a ΔTc ≈ 10 K in a dc SQUID measurement. The ferroelectric properties of the capacitors were characterized by a RT66A apparatus.

Tem Study of Interfaces And Defects in Mocvd-Grown Gan on Sic on Simox

AbstractSiC was grown on the top Si layer of SIMOX by carbonization followed by chemical vapor deposition (CVD). Subsequently, GaN was deposited on the SiC by metalorganic (MO)CVD to produce a GaN/SiC/Si/SiO2/Si multilayer structure. This multilayer film was investigated by conventional transmission electron microscopy (TEM) and high resolution (HR)TEM using cross-sectional thin foils. The GaN layer was found to consist of predominately hexagonal gallium nitride (h-GaN), and a smaller fraction of cubic GaN (c-GaN) crystallites. The orientation relationship between most of the h-GaN grains and cubic SiC (3C-SiC) was found to be (0001)GaN//(1I1)sic; [1120]GaN//[110]SiC, while most of the c-GaN grains had an orientation relationship (001)GaN//(001)SiC; [110]GaN//[110]SiC with respect to the 3C-SiC substrate. The hexagonal grains of GaN were found to grow as two variants. In this paper, the defects in both h-GaN and c-GaN are characterized and discussed.

Growth and electronic properties of epitaxial TiN thin films on 3C-SiC(001) and 6H-SiC(0001) substrates by reactive magnetron sputtering

Epitaxial TiN films were grown on cubic (3C)-SiC(001) and hexagonal (6H)-SiC(0001) substrates by ultrahigh vacuum reactive magnetron sputtering from a Ti target in a mixed Ar and N2 discharge at a substrate temperature of 700 °C. Cross-sectional transmission electron microscopy, including high-resolution imaging, showed orientational relationships TiN(001)‖3C-SiC(001), and TiN[110]‖3C-SiC[110], and TiN(111)‖6H-SiC(0001) and . In the latter case, twin-related TiN domains formed as the result of nucleation on SiC terraces with an inequivalent stacking sequence of Si and C. The TiN/SiC interface was locally atomically sharp for both SiC polytypes. Defects in the TiN layers consisted of threading double positioning domain boundaries in TiN(111) on 6H-SiC. Stacking faults in 3C-SiC did not propagate upon growth of TiN. Room-temperature resistivity of TiN films was ρ = 14 μΩ cm for 6H-SiC(0001) and ρ = 17 μΩ cm for 3C-SiC(001) substrates. Specific contact resistance of TiN to 6H-SiC(0001) was 1.3 3 10−3 Ω cm2 for a 6H-SiC substrate with an n-type doping of 5 × 1017 cm−3.

Observation of MBE-grown [formula omitted] and [formula omitted] interfaces by high resolution transmission electron microscope

Interface structures of cubic-GaN on GaAs and 3C-SiC substrates grown by gas-source molecular beam epitaxy using NH 3 plasma were examined by high resolution transmission electron microscopy. There is no intermediated layer at the interface for both the structures. It was found that there are pyramid-like structures formed by (111) facets at cubic-GaN GaAs interfaces and its interface is fairly rough. On the contrary, interfaces of cubic-GaN 3 C-SiC are quite flat without specific structures, which results in good quality GaN epilayers.

Structural and Optical Characterization of High-Quality Cubic GaN Epilayers Grown on GaAs and 3C-SiC Substrates by Gas-Source MBE Using RHEED In Situ Monitoring

ABSTRACTBy monitoring RHEED reconstruction patterns during gas source molecular beam epitaxy growth, the optimization of the growth for cubic GaN was carried out successfully. Cubic GaN epilayer having a X-ray diffraction width of 16min and a low temperature photoluminescence emission width of 19meV was obtained on a 3C-SiC substrate by adjusting the effective III/V ratioin-situduring the growth, which can be inferred from the surface reconstruction transitions. It was found that the surface reconstructions of cubic GaN surfaces are good indices for the optimization of growth parameters.

Growth of Cubic GaN by MBE and Its Properties

ABSTRACTMolecular beam epitaxy (MBE) technique is a useful method to grow III-V nitrides, especially those having a metastable crystal structure, like cubic GaN (c-GaN), because of the capability of in situ observation of growing surfaces and its non-equilibrium growth mechanism. We have grown c-GaN on GaAs and 3C-SiC substrates by gas source MBE using dimethylhydrazine or activated nitrogen beam as an N source, and measured their luminescent and optical properties. This paper summarizes the MBE growth and properties of c-GaN, comparing with those of hexagonal one, and the control of the crystal structures is discussed in terms of growth method, orientation of substrate surfaces and growth conditions.

Surface Reconstructions and III-V Stoichiometry: The Case of Cubic and Hexagonal GaN

ABSTRACTSurface reconstructions for MBE grown GaN are identified. Different cases are considered according to the type of substrate or crystal symmetry and surface phase diagrams are obtained. Through different examples, it is shown how growth monitoring can be efficiently achieved through the use of surface reconstructions. Finally, from the observation that a residual arsenic overpressure in the MBE chamber changes the surface reconstructions of cubic (001) GaN grown onto 3C-SiC (001) substrates to that commonly observed for GaN growth on (001) GaAs, it is proposed that arsenic might be a surfactant for nitride growth.

Epitaxial growth of cubic and hexagonal GaN by gas source molecular beam epitaxy using a microwave plasma nitrogen source

Cubic and hexagonal GaN epilayers were successfully grown on GaAs substrates by gas source molecular beam epitaxy using a microwave plasma nitrogen source. These GaN epilayers showed quite strong cathodoluminescence emission. X-ray and electron diffraction analyses indicated the improved crystalline quality, compared with GaN epilayers grown using dimetylhydrazine. GaN epilayers were also grown, by the same method, on 3C-SiC substrates, which have a lattice constant much closer to GaN than GaAs.

Thermo-Mechanical Ni50Ti50/Si Composite Thin Film Switch

AbstractThe mechanical properties of Ni50Ti50 deposited on Si and 3C-SiC substrates were studied focussing on the interaction of the film and substrate. This interaction determines the transformation characteristics through interface accommodation and mechanical constraints exerted by the substrate stiffness. Substrate stiffness, controlled by the film/substrate thickness ratio, was found to have a substantial influence on the output energy of the film/substrate composite. A switch type composite based on this knowledge was fabricated and tested.

ガスソース分子線を用いたシリコンカーバイド単結晶成長の原子層制御

Atomic-layer level control in SiC crystal growth using gas source molecular beam epitaxy was demonstrated. Alternate supply of source gases of Si2H6 and C2H2 induced the transitions of surface superstructures. When Si2H6 was supplied, Si atoms generated by thermal decomposition were adsorbed on a 3C-SiC (001) substrate, which brought about the change of surface superstructures from the initial c (2×2) to the sequential evolution of (2×1), (5×2) and (3×2) corresponding to the increase of constituent Si atoms. When C2H2 was supplied, the adsorbed Si atoms reacted with the C2H2 molecules, resulting in crystallization of SiC, and the superstructure showed the initial c (2×2) pattern. The growth rate seemed to be regulated by the limited number of Si atoms forming superstructures. Detailed analysis of in-situ dynamic RHEED observation revealed the proper configuration of surface superstructures, and the possibility of one-monolayer growth of 3C-SiC was discussed

Single crystal growth of hexagonal SiC on cubic SiC by intentional polytype control

Crystal growth of SiC on 3C-SiC(100) substrates has been carried out by using a sublimation method, utilizing the phase transformation from cubic 3C-SiC to hexagonal 6H-SiC at high temperatures. Polytype control in SiC growth on CVD-grown 3C-SiC(100) substrates was successfully achieved for the first time. The growth rate was several hundred microns per hour. The polytypes and crystallographic planes of the grown layers were examined using photoluminescence, Raman spectroscopy, X-ray diffraction and RHEED analyses. The polytypes of the grown layers change from cubic 3C modification to hexagonal 6H modification with increase in temperature. 6H-SiC with (01 1 4) planes can be grown on 3C-SiC(100). Ingots of 6H-SiC up to 15 mm in diameter and 6 mm in length were grown in 6 h. The grown mechanism of 6H-SiC on 3C-SiC substrates based on the experimental results is discussed.