M. G. Mynbaeva

On Current Limitations in Porous SiC Applications

Thermal stability of porous SiC (PSC) with nano-, micro- and double-layer porous structure is assessed through annealing the material at T=900–1700 0C in vacuum and Ar. Changes in composition of PSC under thermal treatment are correlated with porous structure modification. Limitations in PSC technology and applications due to compositional and structure evolution at high temperatures are discussed.

Porous SiC for HT Chemical Sensing Devices: an Assessment of its Thermal Stability

Porous silicon carbide substrates produced by anodization that are intended for use in chemical sensing solid state devices that will operate at high temperatures (at or above 900°C) have been studied with a view to assessing the structural stability/pore modification processes occurring during thermal processing. Annealing experiments were performed using n-type porous 4H-SiC (PSiC) in the temperature range of 900°C-1700°C in Ar atmosphere. The samples were kept at the desired temperatures for 30 minutes. The morphology of the as-received samples consisted of welloriented pores along the <041> direction. Signinficant pore modification occurred at 1400°C. The thickness of the porous layer was reduced following heating at 1700°C. The suitability of PSiC as a chemical sensing element is discussed.

Low-temperature transport properties of multigraphene films grown on the SiC surface by sublimation

Multigraphene films grown by sublimation on the surface of a semi-insulating 6H-SiC substrate have been studied. It is shown that pregrowth annealing of the substrate in a quasiclosed growth cell improves the structural quality of a multigraphene film. Ohmic contacts to the film have been fabricated, and the Hall effect has been studied at low temperatures. It is found that a 2D electron gas exists in the films. It is concluded that the conductivity of the film is determined by defects existing within the graphene layer or at the interface between the graphene film and a SiC substrate.

High-temperature diffusion doping of porous silicon carbide

The results of experiments on high-temperature (2000–2200°C) diffusion doping of porous silicon carbide (PSC) by vanadium and erbium are reported. It is established that the specific features of diffusion processes in PSC at these temperatures are determined by modification of the porous structure due to the transport of vacancies. Based on a comparison of these results to available data on the low-temperature (900–1000°C) diffusion, it is concluded that the mechanisms of diffusion in PSC at low and high temperatures are different and that SiC with a porous structure is an effective medium particularly for low-temperature diffusion.

Electrical characteristics of multigraphene films grown on high-resistivity silicon carbide substrates

Multigraphene films grown by sublimation of the surface of semi-insulating 6H-SiC substrates in a vacuum have been studied. The films exhibit a semiconductor-type conductivity. A conclusion is made that this type of conduction is supposedly determined by defects present between separate graphene crystals constituting the carbon layers under study.

EPR Studies of Interface Defects in n-Type 6H-SiC/SiO2 Using Porous SiC

To overcome the previous unsuccessful attempts for the study by Elect ron Paramagnetic Resonance (EPR) spectroscopy of the defects at the 6H-SiC/SiO 2 interface we have studied thermally oxidised porous SiC layers. Two paramagnetic defects w ere detected after furnace oxidation at 1000°C. The first defect is characterised by an EPR spe ctrum with axial symmetry and g-factors of g//=2.0023 and g ⊥=2.0031 and a superhyperfine structure of 11.3G with three Si neighbour atoms. From the analogy between this defect and the Pb centre s at th Si/SiO2 interface we attribute this defect to a •-C-Si3 carbon dangling bond centre in the SiC interface plane. The second centre has an isotropic g value of 2.0028 and is tentatively attri buted to a C related defect in the non stoichiometric oxide in the near interface region.

Radiation hardness of n-GaN schottky diodes

Schottky-barrier diodes with a diameter of ~10 µm are fabricated on n-GaN epitaxial films grown by hydride vapor-phase epitaxy (HVPE) on sapphire substrates. The changes in the parameters of the diodes under irradiation with 15 MeV protons are studied. The carrier removal rate was found to be 130–145 cm–1. The linear nature of the dependence N = f(D) (N is the carrier concentration, and D, the irradiation dose) shows that compensation of the material is associated with transitions of electrons from shallow donors to deep acceptor levels which are related to primary radiation defects.

Graphene/silicon carbide-based scaffolds

3D-SiC/2D-C structures were fabricated from SiC wafers by first producing a micro-porous material by anodization, and then using a two-step annealing process to modify the porous matrix and initiate the formation of a 2D-carbon coating through a self-organized process. Topological features of the obtained structures extend from the macro- down to the nano-scale. It is expected that such a topology, in combination with the high corrosion resistance and bio-compatibility of both SiC and nano-carbon, will make the 3D-SiC/2D-C structures suitable for applications in bio-engineering.

Diffusion in porous silicon carbide

By the example of vanadium and erbium diffusion in porous silicon carbide, the semiconductor porous structure modification during thermal annealing has been simulated and the effect of this modification on impurity diffusion has been considered. A comparison of calculated and experimental profiles of the erbium and vanadium distributions in porous silicon carbide shows that the consideration of porous structure modification due to vacancy redistribution makes it possible to adequately describe diffusion in the porous semiconductor.

New approach to rapid characterization of single-crystalline silicon carbide

A new approach to the characterization of single-crystalline silicon carbide (SiC) ingots is proposed, which can be used for the rapid diagnostics of material quality under large-scale commercial production conditions. The proposed method can reveal various defects, such as polytype inclusions, small-angle grain boundaries, dislocations, micropipes, and inhomogeneous dopant distribution and can be used to optimize technological regimes for growing bulk SiC single crystals.