We present epitaxial graphene (EG) growth on nonpolar 6H-SiC-faces by solid-state decomposition of the SiC substrate in the Knudsen flow regime in vacuum. The material characteristics are compared with those known for EG grown on polar SiC-faces under similar growth conditions. X-ray photoelectron spectroscopy (XPS) measurements indicate that nonpolar faces have thicker layers than polar faces. Among nonpolar faces, the m-plane (11̅ 00) has thicker layers than the aplane (112̅ 0). Atomic force microscopy (AFM) shows nanocrystalline graphite features for nonpolar faces, consistent with the small grain size measured by Raman spectroscopy. This is attributed to the lack of a hexagonal template, unlike on the polar Si-and C-faces. These nonpolar face EG films exhibited stress decreasing with increasing growth temperature. These variations are interpreted on the basis of different growth mechanisms on the various faces, as expected from the large differences in surface energy and step dynamics on the various SiC surfaces. Surfaces with smaller grain sizes systematically exhibited thicker layers. Using this observation, we argue that multilayer EG growth, after the nucleation of the first layers, is determined primarily by Si diffusion through grain boundaries and defects, as Si cannot diffuse through a perfect graphene lattice. A greater density of grain boundaries allows more Si to escape during growth, allowing thicker layers of carbon to be grown.

As-deposited Ni/SiC Schottky diodes often show nonideal forward conduction characteristics. The ideality can be improved by the formation of a nickel-silicide/SiC interface by annealing at >650°C. The nonideal characteristics in as-deposited diodes are generally attributed to Schottky barrier inhomogeneity at the interface. However, recent studies show that highly nonideal characteristics (n > 1.2) cannot be explained by the existing inhomogeneity models. In this paper, we report the observation of hysteresis patterns in the I-V and CV characteristics of as-deposited nonideal diodes. It is argued that the existence of evenly distributed slow, donor-like interface traps can explain the hysteresis and the associated Schottky nonideality. A trap density of 10 8 -10 10 cm −2 was estimated from the I-V and CV hysteresis. IndexTerms-Barrier height, interface trap, metal-semiconductor junction, Schottky diode, silicon carbide.

In this letter, we report the UV detection characteristics of an epitaxial graphene (EG)/SiC based Schottky emitter bipolar phototransistor (SEPT) with EG on top as the transparent Schottky emitter layer. Under 0.43 μW UV illumination, the device showed a maximum common emitter current gain of 113, when operated in the Schottky emitter mode. We argue that avalanche gain and photoconductive gain can be excluded, indicating minority carrier injection efficiency, γ, as high as 99% at the EG/p-SiC Schottky junction. This high γ is attributed to the large, highly asymmetric barrier, which EG forms with the p-SiC. The maximum responsivity of the UV phototransistor is estimated to be 7.1 A/W. The observed decrease in gain with increase in UV power is attributed to recombination in the base region, which reduces the minority carrier lifetime.

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We present a quantitative study on the growth of multilayer epitaxial graphene (EG) by solid-state decomposition of SiC on polar (c-plane Si and C-face) and non-polar (a and m planes) 6H-SiC faces, with distinctly different defect profiles. The growth rates are slower than expected from a mechanism that involves Si loss from an open and free surface, and much faster than expected for the nucleation of a defect-free EG layer, implying that defects in the EG play a critical role in determining the growth kinetics. We show that a Deal-Grove growth model, which assumes vertical diffusion of Si through these defects as the limiting factor for EG growth, is unsuitable for describing multilayer growth. Instead, we introduce a lateral “adatom” diffusion mechanism for Si out-diffusion, based on a modified Burton, Cabrera, and Frank model. In this model, defects in epitaxial graphene serve as sinks for Si desorption loss, taking the place of reactive sites, such as step edges for nucleation and growth of crystals produced with external precursors. This analysis shows that the surface diffusion of Si atoms to the grain boundaries of EG limits the growth on c-plane C-face and non-polar faces, rather than the purely vertical diffusion of Si through the grain boundaries described in the Deal-Grove model. However, for Si-face c-plane growth, diffusion of Si to the defects, as well as desorption of Si at the grain boundaries are both relevant, leading to a different temperature trend compared with the other faces. This distinct qualitative difference is ascribed to point-defects in Si-face growth, as contrasted with line defects/grain boundaries on the other faces. The size of the EG grains correlates with the surface diffusion length extracted from this model. The longer a Si adatom diffuses, the higher the quality of the grown EG film, an insight that provides valuable information on Si adatom kinetics for optimizing EG growth. We discuss the applicability of this model to growth of multilayer EG in an argon ambient at atmospheric pressure.

Step flow epitaxial growth was achieved on 1° offcut 6H-SiC substrate using dichlorosilane (DCS) as the Si precursor. High crystal quality and polytype uniformity were verified by XRD and Raman spectroscopy. Mirror-like surfaces with very few triangular and carrot defects were obtained over a wide range of C/Si ratios. Surface step bunching and step crossover were observed and rms roughness values were measured to be 2–4 nm. N-type doping was achieved by site-competition epitaxy at low C/Si ratios. Growth rates of 0.5−4 μm/h was obtained over a temperature range of 1470–1550 °C. The surface diffusion length of the adatoms on the step terraces was calculated using a model based on the Burton-Cabrera-Frank theory of epigrowth on stepped surfaces. In the experimental temperature range, the surface diffusion length varied from 5 to 13 nm, which is significantly shorter than those reported in literature for epigrowth using the conventional silane precursor. The short diffusion lengths for DCS imply a strong desorption process at the growth front, which is ideal for polytype-matched step-flow growth on low offcut substrates. The understanding of these step dynamics issues is critical for crystal growers using chlorinated gas precursors.

Room temperature photoluminescence was obtained by UV excitation of homoepitaxially grown 4H-SiC thin films. A broad band emission from boron deep levels centered at 517nm was observed along with the band-edge emission of 4H-SiC at 391 nm. The wavelength of the excitation was varied and the change in the relative intensity of the two emission peaks was observed. The variation of the relative intensity was correlated with the in-grown stacking fault density in the epilayer. A physical model was developed to explain the correlation in terms of carrier diffusion length. For epilayers with very high density of in-grown stacking faults, a sharp emission was observed at 480nm.

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