3C-SiC Surface Research Articles

Macroscopic electron-hole distribution in silicon and cubic silicon carbide by the intense femtosecond laser pulse

Electron excitations at silicon and cubic silicon carbide (3C-SiC) surfaces caused by an intense femtosecond laser pulse are calculated by solving the time-dependent density functional theory and Maxwell’s equation simultaneously. The energy absorption, carrier density, and electron-hole quasitemperatures decrease exponentially in 100 nm from the surface. The electron and hole quasitemperatures have finite values even at large distances from the surface because of a specific photoabsorption channel. Although the quasitemperature in the silicon shows a smooth exponential decrease, 3C-SiC shows the stepwise decrease because of the change of concerning bands. The quasitemperature depends not only on the excitation process, i.e., tunnel and multiphoton absorption, but also on the band structure significantly.

Effect of stretching on the initial oxidation of 3C-SiC nanowire by first-principle simulation

To understand the initial oxidation of the stretched perfected 3C-SiC nanowire, the stable atomic configurations of an O atom adsorption on the 3C-SiC (1¯21¯) surface were investigated by first-principle calculation. The results show that the stress-free 3C-SiC (1¯21¯) has 1 × 2 periodicity due to the surface reconstruction. The strongest O atom adsorption happens at B2–3 site in the stretched 3C-SiC (1¯21¯) with the adsorption energy around −5.6 eV, consistent with the results of the stress-free 3C-SiC (1¯21¯). This is because that the relative position between the O atom and the oxidized Si atoms does not change with the stretching. The adsorption energies of the O atoms at T-1, T-5, T-6 and B-6 sites on the surface of the stretched 3C-SiC (1¯21¯) increase, resulting from the decreased stability of the topmost oxidized Si atoms and the outstretched distance between two Si atoms. Therefore, though 3C-SiC nanowires are used as reinforcements under tensile strain in practical applications, the stretched perfected nanowires aren't easilier oxidized than the stress-free ones with retaining their toughening effect.

Atomic insight into concurrent He, D, and T sputtering and near-surface implantation of 3C-SiC crystallographic surfaces

Abstract We present results from atomistic simulations of sputtering and near-surface implantation of concurrent He, D, and T bombardment of cubic silicon carbide (3C-SiC). This is achieved by first establishing a many-body interatomic potential parameter set to treat interactions of He and hydrogenic species in 3C-SiC informed by ab-initio calculations. To obtain sputtering yields we perform both classical molecular dynamics and binary collision approximation simulations for normal incident particles having energies ranging from 25 to 800 eV. We find that due to differences in species surface binding energy of various crystallographic surfaces in 3C-SiC, the sputtering yield of Si is significantly less than that of C, but sputtering yields show limited sensitivity to crystallographic surface orientation. An exception to this occurs when the terminating crystallographic surface plane is more rich in Si rather than C, resulting in comparable sputtering yields of Si and C. The influence of temperature on sputtering is explored and shows limited effect. Finally, the nature of implanted He, D, and T within 3C-SiC surfaces is investigated to understand implantation profiles and stability of defects.

Stepped morphology on vicinal 3C- and 4H-SiC (0001) faces: A kinetic Monte Carlo study

Stepped morphologies on vicinal 3C- and 4H-SiC (0001) surfaces with the miscut toward [11¯00] or [112¯0] directions have been studied with a three-dimensional kinetic Monte Carlo model. In the model, a three-dimensional lattice mesh was established based on the crystal lattice of 3C-and 4H-SiC to fix the positions of atoms and interatomic bonding. Periodic boundary conditions were applied in the lateral direction while helicoidal boundary conditions were used in the direction of crystal growth. Events, such as adatoms attachment, detachment and interlayer transport at the step edges, and adatoms adsorption and diffusion on the terraces were considered in the model. Effects of Ehrlich–Schwoebel barriers at downward step edges and incorporation barriers at upwards step edges were also considered. Moreover, the atoms of silicon and carbon were treated as the minimal diffusing species independently to achieve more elaborate information for the behavior of atoms in the crystal surface. The simulation results showed that multiple-height steps were formed on the vicinal 4H-SiC (0001) surfaces, whereas single bilayer-height stepped morphologies were observed on the vicinal 3C-SiC (0001) surfaces. Furthermore, zigzag shaped edges were observed for both of 3C- and 4H-SiC (0001) surfaces with the miscut toward [112¯0] direction. At last, the formation mechanism of the stepped morphology was also analyzed.

Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3C[sbnd]SiC (111)

Multilayer graphene has exhibited distinct electronic properties such as the tunable bandgap for optoelectronic applications. Among all graphene growth techniques, thermal decomposition of SiC is regarded as a promising method for production of device-quality graphene. However, it is still very challenging to grow uniform graphene over a large-area, especially multilayer graphene. One of the main obstacles is the occurrence of step bunching on the SiC surface, which significantly influences the formation process and the uniformity of the multilayer graphene. In this work, we have systematically studied the growth of monolayer and multilayer graphene on off-axis 3CSiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3CSiC steps, we demonstrate that the step bunching can be fully eliminated during graphene growth and large-area monolayer, bilayer, and four-layer graphene can be controllably obtained on high-quality off-axis 3CSiC(111) surface. The low energy electron microscopy results demonstrate that a uniform four-layer graphene has been grown over areas of tens of square micrometers, which opens the possibility to tune the bandgap for optoelectronic devices. Furthermore, a model for graphene growth along with the step bunching elimination is proposed.

Investigating positive oxide charge in the SiO2/3C-SiC MOS system

This paper investigates the origin of the fixed positive oxide charge often experimentally observed in Metal Oxide Semiconductor (MOS) structures of SiO2 formed on cubic silicon carbide (3C-SiC). The electrical properties of MOS structures including either thermally grown SiO2 or deposited SiO2 by Plasma Enhanced Chemical Vapour Deposition (PECVD) on epitaxial 3C-SiC layers grown directly on Si are investigated. MOS structures with a range of oxide thickness values subjected to different thermal treatments were studied. It was found that both thermally grown and deposited SiO2 on 3C-SiC exhibit similar positive charge levels indicating that the charge originates from interface states at the 3C-SiC surface and not from the oxide. The nature of this surface charge in the SiO2/3C-SiC system is also discussed based on the current data and previously published results.

Silicon (001) Heteroepitaxy on 3C-SiC(001)/Si(001) Seed

We report for the first time the successful heteroepitaxial growth of Si(100) oriented layer on top of a 3C-SiC(001) seed. By using a post-growth modification of the 3C-SiC surface (pulse insertion of precursors during cooling), it led to a change in Si nucleation, favoring squared (100) islands instead of elongated (110) ones. Without this surface modification step, the Si layers grown on 3C-SiC were always polycrystalline with a mixture of (110) and (100) orientations. Using such Si(100) layer grown on top of 3C-SiC(100), a (100) oriented 3C-SiC single crystalline layer was successfully grown on top, fabricating thus for the first time a fully (100) oriented multilayer heterostructure made of Si(substrate)/SiC/Si/SiC.

Investigation on the Wetting Behavior of 3C-SiC Surfaces: Theory and Modeling

Silicon carbide (SiC) is a promising material for high-power and high-frequency electronics due to its wide band gap, large breakdown field, and high thermal conductivity. Several applications of micro- and nanoelectronics are found in aqueous environments; thus, it is important to understand the atomic-scale interactions between SiC and water, as these interactions govern the transport processes at solid–liquid interfaces. In an effort to characterize the solid–liquid interactions, the wetting behavior of 3C-SiC was numerically investigated. The wettability of two crystallographic planes ((100) and (111)) was characterized, allowing to have silicon or carbon terminations. It was found that the crystallographic planes as well as the atomic surface terminations play an important role in the wetting behavior of 3C-SiC. Higher hydrophilicity was observed for the Si-terminated surfaces as well as for the SiC(111) crystallographic plane. A combination of a mean-field model of wettability and an analysis of the...

The (001) 3C SiC surface termination and band structure after common wet chemical etching procedures, stated by XPS, LEED, and HREELS

The (001) surface of cubic silicon carbide (3C SiC) after cleaning, Ar sputtering and three different wet chemical etching procedures was thoroughly investigated via (angle resolved) XPS, HREELS, and LEED. While Ar sputtering was found to be unsuitable for surface preparation, all three employed wet chemical etching procedures (piranha/NH4F, piranha/HF, and RCA) provide a clean surface. HF as oxide removal agent tends to result in fluorine traces on the sample surface, despite thorough rinsing. All procedures yield a 1 × 1 Si–OH/C–H terminated surface. However, the XPS spectra reveal some differences in the resulting surface states. NH4F for oxide removal produces a flat band situation, whereas the other two procedures result in a slight downward (HF) or upward (RCA) band bending. Because the band bending is small, it can be concluded that the number of unsaturated surface defects is low.

RHEED intensities from two-dimensional heteroepitaxial nanoscale systems of GaN on a 3C-SiC(111) surface

This paper presents a version of simulation program, which facilitates the calculation of changes to the intensity of RHEED oscillations in the function of the glancing angle of incidence of the electron beam, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal (0001) GaN film nucleated on a 3C-SiC surface, including the possible existence of various diffuse scattering models through the layer parallel to the surface. New version program summaryTitle of program: RHEED_DIFF_ZProgram Files doi:http://dx.doi.org/10.17632/52nxmwzkxx.1Licensing provisions: GNU General Public License 3Programming language used: C++Journal reference of previous version: Computer Physics Communications 207 (2016) 536–538Does the new version supersede the previous version?: No. It is a supplement to the previous version.Reasons for new version:Responding to users’ feedback we present a practical procedure of construction of simulation program, which facilitates the calculation of changes to the intensity of RHEED rocking curves, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal (0001) GaN film nucleated on a 3C-SiC(111) surface.Nature of problem:Growth of GaN layers on SiC is of importance for potential electronic device applications.Silicon carbide crystallizes in numerous different modifications, so-called polytypes [1]. Among them, only hexagonal structure 4H-SiC and 6H-SiC have been thoroughly investigated while the cubic 3C-SiC polytype is lagging behind in technological developments. The 3C-SiC has a Zincblende crystal structure and is characterized by an identical orientation of all bilayers in the crystal, where the atomic geometry is repeated every three bilayers along the c-axis this crystal structure (Fig. 1). For this reason, 3C-SiC has the high electron mobility and saturation velocity by reducing phonon scattering resulting from the high symmetry. The lattice mismatch between GaN(0001) and 3C-SiC(111) is about 3.3%, and is smaller than the mismatch between GaN(0001) and Si(111) [2]. Therefore progress in investigations on crystal growth of GaN on 3C-SiC is a key issue for device developments related to this heterostructure. Researchers and technologists manufacturing two-dimensional heterostructures frequently use RHEED rocking curves to control growth of samples at the atomistic level of accuracy. The fundamental scientific problem in such research is to specify both interface type and growth mechanism for subsequent layers.Method of solution:RHEED intensities are calculated within the general framework described in Refs. [2] and [3].Summary of revisions:The presented version of the program implements an original algorithm of self-consistent calculations for scattering potentials GaN(0001)/3C-SiC(111) and solving a time-independent Schrödinger equation for high-energy electrons.During the numerical calculations of the changes in the intensity of the specular beam in the function of the glancing angle, it was assumed that the azimuth of the incident beam direction corresponds to the one-beam condition, the electron energy equals 10 keV, the glancing angle was increased from 0.5∘ to 6.5∘, and the value of αparameter=0.1 and β=0.5 for the MODEL3 of the scattering potential [3] with the model of ideal SiC/GaN interface [4].

(Invited) P-Type 3C-SiC Photocathode for Solar to Hydrogen Energy Conversion

Solar to hydrogen conversion technology attracts attention as renewable energy generation. In general, to perform solar to hydrogen conversion, photocatalytic materials are employed. However, most of photocatalytic materials cannot absorb visible light resulting in low conversion efficiency and degrade during operation. Thus, we need to find new photocatalytic materials which have both high conversion efficiencies and resistance to corrosion. Silicon carbide (SiC) is a chemically stable and photocatalytic semiconductor material. SiC can be grown by different atomic configurations resulting in a large number of polytypes. Among SiC polytypes, 3C-SiC has the smallest band gap (2.3 eV), and thus 3C-SiC is capable to absorb significant part of solar light. In addition, conductive type of SiC can be controlled by doping. Photocatalytic materials with p-type conduction operate as cathode and reduce hydrogen in water. Cathodic operation prevents oxidation of photocatalytic materials. Therefore, p-type 3C-SiC will be an efficient and durable photocatalyst. However, bulk crystal growth of 3C-SiC is very difficult because this polytype is stable only in growth at much lower temperature than sublimation of SiC, which is a typical condition for bulk SiC growth. This difficulty makes 3C-SiC growth only by chemical vapor deposition (CVD) on Si or 4H- or 6H-SiC substrates. Such the heteroepitaxial growth induces large number of structural defects or polytype mixing owing to lattice mismatch or inheritance of the substrate polytype. For our recent 3C-SiC photocathode fabrication, we employed p+-type 4H-SiC substrates with the (0001) Si-face inclined 0.7° to <1120> direction. Growth on the 4H-SiC substrates with quasi on-axis Si-face prevents polytype mixing and p+-type conductivity of the substrate facilitates ohmic contact formation on the substrate side. We performed 3C-SiC growth on the substrates by CVD with silane and propane as source gases and in an Al acceptor doping condition. A photograph of the grown crystal is shown in Fig. 1(a). After the growth, we fabricated ohmic contact on the substrate side of the crystals. The 3C-SiC surface is active surface as the photocathode. In addition, we formed Pt or Pd cocatalysts on the 3C-SiC surface to enhance hydrogen generation by the photocathodes. The schematic of the photocathode structure is shown in Fig. 1(b). We measured photocurrent-potential characteristics for the photocathodes in 1 M H2SO4 aqueous solution using chopped solar simulator light with 100 mW/cm2. The results are shown in Fig. 1(c). For bare surface, cathodic photocurrent was observed below 0.6 V vs SCE, and it reached -1.4 A/cm2 at -1 V vs SCE. On the other hand, with cocatalysts, photocurrents were observed at higher potential, and in the case of with Pt cocatalysts, it was observed from 0.9 V vs SCE. In addition, at -1 V vs SCE, the photocurrent was -2.3 A/cm2. In solar to hydrogen conversion, the Faraday efficiencies of the photocathodes were near to 100% and the photocathodes were not degraded during experiments. Solar to hydrogen conversion efficiency for the photocathode with Pt cocatalysts was 0.52 %. Considering such a high efficiency and possibility of further improvement, SiC is a very promising material for the solar to hydrogen conversion technology. Figure 1

Improved performance of 3C[sbnd]SiC photocathodes by using a pn junction

To improve the performance of 3CSiC photocathodes, we formed a pn junction at the 3CSiC surface. Using current–voltage measurements for Schottky contacts on 3CSiC, the Schottky barrier height and depletion layer width of 3CSiC having a pn junction was observed to be larger than those of 3CSiC without the junction. By measuring photocurrent and spectral responses, the 3CSiC photocathodes with the pn junction exhibited larger photocurrent and higher quantum efficiencies compared with 3CSiC without the pn junction. Using a Pt cocatalyst on the 3CSiC photocathode with the pn junction, the solar-to-hydrogen energy conversion efficiency was measured at 0.72%.

Effect of ion-beam irradiation on the epitaxial growth of graphene via the SiC surface decomposition method

We used scanning tunneling microscopy, low-energy electron diffraction, and Raman spectroscopy to investigate the growth of graphene on 3C-SiC(111)/SiO2/Si(111) surfaces with ion-beam irradiation via the SiC surface decomposition method. We were unable to obtain graphene after annealing the 3C-SiC(111) surface at 1100 °C for 3 min without Ar+ ion-beam irradiation. When a 3C-SiC(111) surface was irradiated with an Ar+ ion beam at an acceleration voltage of 1 keV and an incident angle of 80° and subsequently annealed at 1100 °C for 3 min, graphene formed on the SiC surface. However, when an Ar+ ion beam was used at an incident angle of 70 or 60°, graphene layers were not formed. These results indicate that the breakage of bonds in the surface region of the SiC(111) substrate by ion-beam irradiation promotes the formation of graphene.

Highly oriented diamond (111) films synthesized by pulse bias-enhanced nucleation and epitaxial grain selection on a 3C-SiC/Si (111) substrate

We report the synthesis of highly oriented diamond (HOD) (111) films on 3C-SiC/Si (111) substrates. Bias-enhanced nucleation (BEN) is a key process for the heteroepitaxial growth of HOD films. Conventional long nucleation periods have been found to lead to a polycrystalline diamond film on the 3C-SiC (111) surface. Here, we propose a method that combines brief BEN (&amp;lt;30 s), called pulse BEN, and epitaxial grain selection by oxidative etching. Smaller diamond nuclei with a higher spatial density on the substrate were formed by pulse BEN with a pulse duration of &amp;lt;30 s. We found that precisely controlling the pulse duration is important for obtaining a nucleation density that is sufficiently high to obtain the HOD films. By adding oxygen gas to the subsequent growth process, non-epitaxial nuclei were removed and epitaxial diamond grains selectively remained. There was no notable difference in the relative growth rate of [111] to [100] with and without oxygen, and the orientation improvement was observed on both the (100) and (111) substrates. This suggests that the mechanism of oxidative removal was not evolutionary selective growth, but etching of the non-epitaxial interfaces between the nuclei and the (111) substrate. Finally, the HOD (111) films covering the entire 3C-SiC surface were synthesized, and they exhibited distinct diffraction spots, indicating the formation of the oriented diamond.

Decoupling and ordering of multilayer graphene on C-face 3C-SiC(111)

We show experimentally that few layer graphene (FLG) grown on the carbon terminated surface (C-face) of 3C-SiC(111) is composed of decoupled graphene sheets. Landau level spectroscopy on FLG graphene is performed using the infrared optical Hall effect. We find that Landau level transitions in the FLG exhibit polarization preserving selection rules and the transition energies obey a square-root dependence on the magnetic field strength. These results show that FLG on C-face 3C-SiC(111) behave effectively as a single layer graphene with linearly dispersing bands (Dirac cones) at the graphene K point. We estimate from the Landau level spectroscopy an upper limit of the Fermi energy of about 60 meV in the FLG, which corresponds to a carrier density below 2.5 × 1011 cm−2. Low-energy electron diffraction μ-LEED) reveals the presence of azimuthally rotated graphene domains with a typical size of ≤200 nm. μ-LEED mapping suggests that the azimuth rotation occurs between adjacent domains within the same sheet rather than vertically in the stack.

Effect of nucleation on instability of step meandering during step-flow growth on vicinal 3C-SiC (0001) surfaces

A three-dimensional kinetic Monte Carlo (KMC) model has been developed to study the step instability caused by nucleation during the step-flow growth of 3C-SiC. In the model, a lattice mesh was established to fix the position of atoms and bond partners based on the crystal lattice of 3C-SiC. The events considered in the model were adsorption and diffusion of adatoms on the terraces, attachment, detachment and interlayer transport of adatoms at the step edges, and nucleation of adatoms. Then the effects of nucleation on the instability of step meandering and the coalescence of both islands and steps were simulated by the model. The results showed that the instability of step meandering caused by nucleation was affected by the growth temperature. And the effects of nucleation on the instability was also analyzed. Moreover, the surface roughness as a function of time for different temperatures was discussed. Finally, a phase diagram was presented to predict in which conditions the effects of nucleation on step meandering become significant and the three different regimes, the step-flow (SF), 2D nucleation (2DN), and 3D layer by layer (3DLBL) were determined.

Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC(001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth.

Comment on “Adsorption of hydrogen and hydrocarbon molecules on SiC(001)” by Pollmann et al. (Surf. Sci. Rep. 69 (2014) 55–104)

This comment clarifies two issues related to the (001) surface reconstructions of cubic SiC, namely: (i) The failure of the bridge-bond model for H atoms interacting with the 3C-SiC(001) 3×2 reconstruction to explain all the experimental data based on different techniques, while a recent model has reconciled theory and experimental results. This model has not been discussed or even mentioned in the review by Pollmann et al.; and (ii) In their review, two models of the Si-terminated c(4×2) 3C-SiC(001) surface reconstruction are presented as equally probable. This is clearly not the case and the reasons are explained in this comment.

Direct insight into grains formation in Si layers grown on 3C-SiC by chemical vapor deposition

This work presents a structural study of silicon (Si) thin films grown on cubic silicon carbide (3C-SiC) by chemical vapor deposition. The presence of grains rotated by 90° around the growth direction in the Si layer is directly related to the presence of antiphase domains on the 3C-SiC surface. We were able to provide a direct evidence that the 90° rotation of Si grains around the growth direction occurs exactly on the termination of antiphase boundaries (APBs) in 3C-SiC layer. Increasing the 3C-SiC thickness reduces the APBs density on 3C-SiC surface leading to a clear improvement of the uppermost Si film crystal quality. Furthermore, we observed by high resolution plan-view TEM images the presence of hexagonal Si domains limited to few nm in size. These hexagonal Si domains are inclusions in small Si grains enclosed in larger ones rotated by 90°. Finally, we propose a model of grains formation in the Si layer taking into consideration the effect of the 3C-SiC thickness.

&lt;i&gt;Ab Initio&lt;/i&gt; Calculations of Absolute Surface Energies of Clean and Hydrogen Covered 3C-SiC(001), (110) and (111) Surfaces

The absolute surface energies of three major low index surfaces of cubic silicon carbide (3C-SiC) are determined by first-principles density functional theory calculations. Calculations show that among clean 3C-SiC surfaces the Si-terminated 3C-SiC(001)-(3x2) surface has the lowest energy. The second and third lowest energy surfaces are the Si-terminated 3C-SiC(111)-(√3x√3) surface and the nonreconstructed 3C-SiC(110) surface. Hydrogen passivation greatly reduces both the absolute surface energies of the low index 3C-SiC surfaces and the surface energy anisotropy. In particular, the surface energies of fully passivated 3C-SiC(110) and (111) surfaces become indistinguishable at hydrogen-rich deposition conditions.