Materials Science Forum Vols. 821-823

Abstract: In this paper we have studied the connection between crystal quality and electrical transport in 4H-SiC by simultaneous micro-photoluminescence (μPL) and micro-photocurrent (μPC) measurements. We have used a focused HeCd laser at 325nm (i.e. above bandgap) to measure with a spatial resolution of few microns both the μPL spectra and the I-V characteristics in 4H-SiC/NiSi Schottky diodes. We found that extended defects exhibiting a photoluminescence peak located at 2.9eV (i.e single Shockley or bar shaped stacking faults) can produce an increase of the measured PC whereas other defects, such as the (4,4) stacking fault, can be considered as ‘killer defects’, strongly reducing the photocurrent.

Abstract: Stable 1D silicon carbide nanostructures (nanowires) have been obtained via combustion synthesis route. Infrared absorption and reflection spectra for as-obtained and purified SiC nanowires were compared with the spectra of commercially available SiC nanomaterials. Principal vibrational modes have been identified. Reflectivity spectrum has been reconstructed by modeling of the dielectric function

Abstract: Room temperature infrared transmittance and reflectance spectra of 4H and 6H-SiC single crystals were measured by a NEXUS 670 Fourier Transform Infrared-Raman spectrometer. The transmittance and reflectance of non-doped, V-doped semi-insulating (SI), high purity semi-insulating, n-type and p-type SiC wafers have been compared and assessed. The effect of nitrogen and boron concentration on the transmittance is discussed. In addition, the carrier concentrations in 4H-SiC wafers were measured by Raman spectroscopy at room temperature. The influence of nitrogen concentration on the transmittance is also discussed.

Abstract: Electronically active dopant profiles of epitaxially grown n-type 4H-SiC calibration layer structures with concentrations ranging from 3.10¹⁵ cm^-3 to 1·10¹⁹ cm^-3 have been investigated by non-contact Scanning Probe Microscopy (SPM) methods. We have shown that Kelvin Probe Force Microscopy (KPFM) and Electrostatic Force Microscopy (EFM) are capable of resolving two-dimensional carrier maps in the low doping concentration regime with nanoscale spatial resolution. Furthermore, different information depths of this wide band gap semiconductor material could be assessed due to the inherent properties of each profiling method. We additionally observed a resolution enhancement under laser illumination which we explain by reduced band-bending conditions. To gauge our SPM signals, we utilized epitaxially grown layers which were calibrated, in terms of dopant concentration, by C-V measurements.

Abstract: In this work we propose a novel approach to measuring doping concentration in SiC based on a micro-scale time-resolved corona-Kelvin technique. In this method corona charging of SiC surface into depletion is done within a micro size corona spot and a Kelvin-force micro-probe is used to measure surface voltage decay in the center of the spot. The voltage decay is due to charge decay due to surface diffusion producing analogy of voltage-charge scanning under the probe. We use 2D charge diffusion analysis to extract two parameters – 1) doping concentration in the SiC epitaxial layer and 2) diffusion coefficient of corona ions on the SiC surface. The micro-spot corona-Kelvin method demonstrated in this work shall prove of importance for testing of doping uniformity on micro scale and measurements on a small area in SiC production wafers.

Abstract: We report on the observation of the THz electroluminescence in 6H-SiC and 8H-SiC n⁺–n^-–n⁺ structures of hexagonal crystals with natural superlattice, caused by applied electrical field along the lattice and natural superlattice axis. It is shown that there are the terahertz electroluminescence correspond to the narrow lines at 5.3–12.7 meV. The emission channel can be well explained by the optical intraladder transitions in the Bloch oscillations regime.

Abstract: 3C-SiC(100) was grown on Si (100) in a thickness range between 40 and 500 nm by low pressure chemical vapor deposition. The mechanical properties and the residual stress were determined using the length dependence of the resonance frequencies of cantilevers and beams. Taking into account the influence of the cantilever bending and the stress gradients the Young’s modulus of the 3C-SiC(100) was obtained. It decreases with decreasing thickness of the epitaxial layer grown on Si (100).

Abstract: Surface defects with scratch-like appearances are often observed locally on 4H-SiC wafers after epitaxial growth. We evaluated such damaged layer which is the cause of local step bunching using Mirror Projection Microscope (MPJ). As a result, MPJ can be detected l damaged layer which could not be detected using Synchrotron X-ray topography, even if these defects are extremely flat surface, no morphology, damaged layer is used to exist on the subsurface region. Thus, MPJ can be detected dislocation loops on the subsurface region of damage, it is effective to elucidate damaged layer of polishing process, MPJ is to be one of the candidates for inspection techniques of the damaged layer at substrate surface.

Abstract: Band-edge (hν_max=3.17-3.18 eV at T=293 K) injection electroluminescence (IEL) characteristics of 4H-SiC pn structures as a function of doping, electron irradiation, temperature, and current are presented. The intensity of the UV band increases with temperature in the range 290-800 K (with an activation energy E_a of about 90 meV), which is observed for the first time in a wide range of current densities from 9 A/cm² up to 2∙10⁴ A/cm². This effect is a fundamental feature of the band-edge IEL in SiC pn structures. The dependence of the intensity L on the current is of the power-law type, L~J^m; at high currents m≈1 at T=650-800 K. This result is probably the first direct observation of the diffusion current in SiC pn structures. The rise in the intensity of the band-edge IEL with increasing temperature and its decrease upon irradiation are probably due to the corresponding change in the lifetime of nonequilibrium carriers.

Abstract: Effects of electron irradiation in n-4H-SiC have been studied by the methods of the capacitance--voltage characteristics and photoluminescence. It was found that the carrier removal rate (Vd) reached a value of ~0, 25 cm^{- 1}. Full compensation of samples with an initial concentration of 1.2 10¹⁵ cm ^-3 was observed at doses of about 5 10¹⁵ cm ^-2. Simultaneously with the increase in the degree of compensation, the intensity of the “defect luminescence”, typical of 4H SiC, became higher. The physical compensation mechanisms were analyzed for the samples under study.