Off-axis Si Research Articles

Growth of high-quality 3C-SiC epitaxial films on off-axis Si(001) substrates at 850 °C by reactive magnetron sputtering

Single crystal 3C-SiC films of thickness ∼10 μm were grown by reactive magnetron sputtering on off-axis Si(001) at 850 °C. The film quality was comparable to the best chemical vapor deposited 3C-SiC as characterized by x-ray diffraction, transmission electron microscopy, and photo- luminescence (PL). The lattice mismatch and difference in thermal contraction between SiC and Si resulted in complete arrays of misfit dislocations at the film/substrate interface and a residual in-plane strain of (−6.9±1)×10−4, respectively. The full width at half-maximum (FWHM) of the 3C-SiC(004) peak was 59 arcsec in ω-2θ direction. The structural defects in the SiC film were planar faults on {111} planes and no voids or plastic deformation in the Si substrate were observed. PL spectra of SiC films showed characteristic appearances with N bound-exciton (N-BE) lines with a FWHM value of 3.4 meV. The deposition conditions leading to low defect-density 3C-SiC films are discussed in terms of low-energy ion-surface interactions.

Defect Reduction of Cvd-Grown Cubic SiC Epitaxial Films on Off-Axis Si(100) Substrates with a Novel Off-Direction.

ABSTRACTMonocrystalline cubic SiC (β -SiC) thin films with lower defect densities have been epitaxially grown by chemical vapor deposition on off-axis Si (100) substrates with off-directions different from the conventional 〈011〉. Stacking faults of β -SiC films are investigated by the electrolytic etching and SEM observation. The effects of off-direction deviated from 〈011〉 are examined for the first time. The off-angle is fixed at 2 degrees. We find a reduction in defect density with increasing deviation angle θ, of off-direction from [011] toward [011[ (θ = 0 - 45°). The defect density becomes one order of magnitude smaller than that of on-axis (100) substrates. A typical value of the stacking fault density is approximately 6 × 106 cm−2 on the substrate with θ = 30° (film thickness: 24μ m).

Characterization of GaAs buffer layers 0.1 μm thick grown on Si(100)

We present Raman scattering measurements for GaAs buffer layers 0.1 μm thick grown on off-axis Si(100) substrates by molecular beam epitaxy. Using the scattering configuration X(YZ) X , only the longitudinal optic (LO) phonon mode is “allowed” and the observation of the “forbidden” transverse optic (TO) phonon reflects the degree of disorder present in the GaAs layer. We have measured the variation of TO:LO intensity as a function of substrate preparation and growth temperature. Our results indicate that buffer layers grown at T≈300 ° C give the lowest TO:LO ratio. Ramping the substrate temperature from T≈300 ° C to T≈580 ° C (the active layer growth temperature) gives rise to a reflection high energy electron diffraction pattern indicative of a (2 × 4) single-domain surface reconstruction and a corresponding decrease in the TO:LO ratio. A comparison is also made of layers of GaAs 4.1 μm thick grown on Si(100) and Si(111) respectively, for identical substrate preparation and buffer layer deposition.

Substrate Dependent Texture and Heteroepitaxy for Group IIIA Nitride Films by the X-Ray Precession Method

ABSTRACTThe X-ray precession method has been utilized to study texture and heteroepitaxy for thin films of the Group IIIA nitrides deposited on a variety of amorphous and single-crystal substrates. Films of InN were synthesized by reactive rfmagnetron sputtering [employing an elemental target and N2 as the sputtering gas], while the GaN films were deposited by metalorganic chemical vapor deposition [utilizing (CH 3 ) 3Ga and NH3 as sources]. The quality of (00.1) textured films of InN on fused quartz and slightly off-axis (111) Si are taken as initial examples of the versatility of the X-ray precession method. The powder rings evolving from a lack of azimuthal coherence for InN films grown on quartz are contrasted with the scattering from weakly correlated (pseudo heteroepitaxial) domains for films grown on (111) Si. These latter scattering features are then compared with those from the true heteroepitaxial deposition of InN onto the (111) face of cubic ZrO2. And, finally, the scattering from the heteroepitaxial growth of InN and GaN on the (00.1) face of sapphire and some initial studies on the effect of nucleation layers on twinning in the GaN films are presented.

Chemical vapor deposition of single-crystal films of cubic SiC on patterned Si substrates

Stacking faults of cubic SiC films grown on Si (100) were investigated by the electrolytic etching. We find an exponential reduction of the defect density with an increase of film thickness and the anisotropy in the density for the films on off-axis Si (100) substrates. The defect reduction along the offset direction 〈011〉 is explained from the atomic step effect limiting the length of stacking faults to smaller than the equilibrium value. In addition, the defects are eliminated by controlling the film thickness and the size of the growth area using patterned substrates. Since the defects in SiC are metastable, the film thickness required for defect-free crystal is larger than √2× the lateral dimension.

An X-ray mask using Ta and heteroepitaxially grown SiC

We have developed an X-ray mask using Ta as the X-ray absorber and heteroepitaxially grown SiC as the X-ray membrane. Ta was reactive ion etched with a Cl 2/CCl 4 gas mixture. Because of the high etching selectivity of Ta to a resist, 0.15 μm line and space patterns could be made using a single layer resist as an etching mask. SiC was heteroepitaxially grown on off-axis Si (111) substrates at 1,000°C with a gas mixture of SiHCl 3/C 3H 8/H 2. The properties were nearly the same as bulk values. The radiation durability was greater than 100 MJ/cm 3. This combination of Ta and SiC is an excellent candidate for use in future X-ray lithography.

A eutectic hydroxide etch for β-SiC

The NaOH-KOH eutectic etch, used at 623 K, reveals antiphase boundaries, stacking faults and dislocations in β-SiC grown on (100) Si substrates. The etch also demonstrates the dramatic reduction in number of antiphase boundaries in β-SiC grown on off-axis (100) Si substrates.

The effect of off-axis Si (100) substrates on the defect structure and electrical properties of β-SiC thin films

Antiphase domain-free, monocrystalline β-SiC thin films have been epitaxially grown on off-axis Si (100) substrates. The effects of degree of misorientation and substrate preannealing on the antiphase domain boundaries (APB's) have been investigated. Wet oxidation, optical microscopy, and transmission electron microscopy were used to characterize the defect structures in both β-SiC thin films grown on exact Si (100) and on off-axis Si (100) substrates. The results revealed that many dislocations were included in APB's and that APB's were eliminated in the β-SiC thin films grown on Si (100) substrates that were oriented 2°–4° from [100] toward the [011] direction. Some APB's were observed near the edge of the β-SiC film on the 2° off-axis Si (100) substrates; however, they were eliminated by substrate preannealing. The carrier concentration and electron mobility of these β-SiC films were similar to those of β-SiC films grown on exact Si (100) substrates as determined by differential capacitance-voltage and Hall effect measurements. Au-β-SiC Schottky diodes were also fabricated on the β-SiC thin films on 4° off-axis substrates and had an ideality factor of 1.4. Differential capacitance-voltage measurements and current-voltage characteristics of Au-β-SiC Schottky diodes indicated that APB's caused significant leakage current in the β-SiC thin films.

An Investigation of the Heteroepitaxial Growth of Beta—silicon Carbide Thin Filmson Silicon Substrates

AbstractHigh purity β—SiC films have been epitaxially grown on Si (100) and off-axis Si (100) substrates. Conventional chemical vapor deposition at 1633K and 1 atm using SiH4 and C2H4 reactants in an H2 carrier gas was employed for this growth. Large differences in lattice parameter and thermal coefficients of expansion between the film and the substrate were partially compensated for by growing aninitial “conversion layer.” Plan view and cross—sectional transmission electron microscopy were utilized to study the conversion layer and the defects present in the films. A high density of stacking faults and dislocations were present in allthe films grown on Si, however, antiphase boundaries were eliminated when certain off—axis Si (100) substrates were employed. The effects of misorientation angle and substrate preannealing were investigated. The electrical properties of the β-SiC films were also studied using differential capacitance—voltage and Hall effect measurements as well as the I—V characteristics of Au—β—SiC Schottky diodes. It was found that the elimination of antiphase boundaries reduced leakage current but did not significantly effect carrier concentration or Hall electron mobility. Finally, the I—V characteristics of a Metal—Semiconductor—Field—Effect—Transistor (MESFET) have been evaluated for a β—SiC filmon an on—axis Si (100) substrate.

Interface formation of GaAs with Si(100), Si(111), and Ge(111): Core-level spectroscopy for monolayer coverages of GaAs, Ga, and As.

The interface structure of thin overlayers of GaAs grown using molecular-beam epitaxy techniques on on-axis Si(100), Si(111), and Ge(111) substrates has been studied using photoemission core-level spectroscopy. Results for As and Ga overlayers are also reported and are utilized to interpret the results for GaAs growth. The interface bonding is found to be the same for growth using predeposition of Ga as for predeposition of As. For GaAs on Si(111), the bonding at the interface is found to consist predominantly of Si-As bonds. We also find strong evidence of island formation before the completion of the first GaAs bilayer. The total area between islands can be reduced either by faster deposition rates or by using a Ga prelayer. For GaAs on Si(100), bonding takes place to both Ga and As but with fewer Si-Ga bonds than Si-As bonds. The tendency to island formation is less than for the Si(111) case. These results are compared with earlier data for As interaction with off-axis Si(100) surfaces to explain the absence of antiphase domains in GaAs grown on off-axis (100) substrates. Roughly equal numbers of Ge-As and Ge-Ga bonds were found for GaAs on Ge(111), and this result is interpreted as indicating thatmore » Ge interdiffuses more rapidly into GaAs than does Si.« less

Improved β-SiC heteroepitaxial films using off-axis Si substrates

All β-SiC films grown using on-axis (001) Si substrates that have been examined with transmission electron microscopy exhibit a high density of interfacial twins, stacking faults, and antiphase disorder. The antiphase boundaries can be decorated by chemical etching, sputter etching, wet oxidation, and β-SiC growth in the presence of diborane. All traces of antiphase disorder are eliminated when the heteroepitaxial growth is carried out on vicinal (001) Si substrates that are tilted 2° about a 〈110〉 axis. In addition, growth on the off-axis Si produces β-SiC films that are significantly smoother than on-axis films. The density of stacking faults is apparently unaffected by growth on the off-axis substrates.