The dependence of surface morphology of the SiC(0001) substrate on the rate with which it is heated up to the temperature of graphene growth was studied by three techniques: atomic force microscopy, Raman spectroscopy and Kelvin probe force microscopy. The study was carried out for the rates of substrates heating ranging from 100 degrees C/min to 320 degrees C/min. As a result, it was found out that both the width of the terraces forming on the surface of SiC substrate and the uniformity of the graphene layers covering these terraces significantly depend on the applied rate of the heating. It was also shown that the most homogeneous monolayer graphene with the minimum of double-layers inclusions is formed if the rate of SiC heating is about 250 degrees C/min.

Abstract. The response of the chips based on graphene films on SiC substrates (the relative change of the chip resistance) on fluorescein (C20H12O5) in a wide range of its concentrations in phosphate-buffered solution from 1 • 10-3 ng/ml, to 1 • 10+4 ng/ml (7 orders of magnitude) is studied. Detection of fluorescein seems to be a simple and cheap model experiment to study a sensing capability of the graphene in the production of biosensors. It was shown that graphene chips with wide terraces on the surface (1000-nm width and 5-nm height) made it possible to plot calibration dependences of the response of the chips on the concentration of fluorescein.

We have studied the response of graphene-film-based chips on SiC substrates (the relative change in the chip resistance) to coming into contact with fluorescein (C 20 H 12 O 5 ) in a wide range of its concentrations in a phosphate-buffered saline solution: from 1 × 10 –3 to 1 × 10 4 ng/mL (seven orders of magnitude). Fluorescein detection seems to be a simple and cheap model experiment to study the sensory ability of graphene in the way of biochips manufacturing. It has been shown that chips with wide terraces on a surface with a step width of about 1000 nm and heights of up to 5 nm made it possible to construct the calibration dependences of chip response on fluorescein concentration.

Treatment of graphene/SiC dies in inorganic electrolytes (KOH, KCl and Na 2 SO 4 ) is discussed. An electrochemical method based on the cyclic voltammetry in a conventional three-electrode cell with Ag/AgCl reference electrode, a platinum counter electrode, and the graphene/SiC dies as working electrode (anode) is used for the treatment. It was observed either partial oxidation of graphene or its complete dissolution with the formation of CO 2 . The treatment performed resulted in the deterioration of the graphene films and change of the graphene-die resistivity depending on the range of the scanning potential applied to the graphene/SiC dies.

We discuss graphene-on-SiC dies for blood-type sensing. For the sensor application, chemical species to be detected adsorb on the graphene surface and act as electron donors or acceptors resulting in resistance changes of the graphene channel. In this work, graphene films were formed on 4H-SiC substrates by thermal decomposition of the (0001) silicon surface in Ar ambient at a high temperature of 1800–2000 oC. The graphene functionalization was performed by the covalent bonding of a nitrophenyl group (C6H5NO2) followed by its reduction to a phenylamine group (C6H5NH2) by using a cyclic voltammetry process. There was a clear and prompt response (current change) of the antibody-coated graphene/SiC dies when the blood antigen matched the antibody. No response occurred when the antibody on the graphene surface mismatched the blood antigen. The experiments demonstrated that a functionalized graphene-on-SiC die has capability in blood sensing, opening a way to manufacture biosensors for detecting blood types and for other applications.

We have studied the effect of temperature and etching duration of the 4H-SiC (0001) surface in hydrogen on the structural perfection of graphene films grown by thermal destruction. Several technological modes have been identified that enable etching of the substrate without changing the stoichiometric composition of the surface. It has been demonstrated that pregrowth etching in hydrogen at T = 1600°C with a duration of 1 min makes it possible to obtain a more uniform and structurally perfect graphene than etching at T = 1300°C with a 30 min duration.

The effect of temperature and duration of the 4H-SiC (0001) surface etching in hydrogen on the structural perfection of graphene films grown by the thermal destruction method was studied. Several technological regimes have been defined that allow etching of the substrate without changing the stoichiometric composition of the surface. It has been demonstrated that pre-growth etching in hydrogen at T = 1600 ° C for 1 min. allows one to obtain more uniform and structurally perfect graphene than etching at T = 1300 ° C for 30 minutes.

We discuss graphene-on-SiC dies for blood-type sensing. For the sensor application, chemical species to be detected adsorb on the graphene surface and act as electron donors or acceptors resulting in resistance changes of the graphene channel. In this work, graphene films were formed on 4H-SiC substrates by thermal decomposition of the (0001) silicon surface in Ar ambient at a high temperature of 1800-2000 degrees C. The graphene functionalization was performed by the covalent bonding of a nitrophenyl group (C6H5NO2) followed by its reduction to a phenylamine group (C6H5NH2) by using a cyclic voltammetry process. There was a clear and prompt response (current change) of the antibody-coated graphene/SiC dies when the blood antigen matched the antibody. No response occurred when the antibody on the graphene surface mismatched the blood antigen. The experiments demonstrated that a functionalized graphene-on-SiC die has capability in blood sensing, opening a way to manufacture biosensors for detecting blood types and for other applications.

Functionalization of graphene/SiC dies by nitro-phenyl and its reduction to phenyl-amine is discussed. The graphene films were formed on a SiC substrate by the substrate surface thermal decomposition at 1800-2000°C. The functionalizing procedure included a two-step electrochemical process monitored by cyclic voltammetry and the die resistance. Functionalized graphene/SiC dies with applied antibody were blood sensitive and can be potentially applied to identify promptly types of the blood.

GaN, GaN/AlGaN and GaN/InGaN-based structures were used to study water photoelectrolysis in KOH-based electrolyte, measurement of current-potential characteristics, investigation of electrode corrosion and for hydrogen generation. The corrosion process of p-n AlGaN/GaN structure starts in the p- layers, spreads via vertical channels associated with threading defects, and continues laterally along the n- layers, where large local hollows and voids were observed. The H 2 production rate of 0.3-0.6 ml/cm 2 ×h was measured for n-GaN structure.

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 rate was found to be 130-145 cm -1 . The linear nature of the dependence N = F (D) (N is carrier concentration, and D, the irradiation dose) shows that compensation of the material is associated with transition of electrons from shallow donors to deep acceptor levels which are related to primary radiation defects.

In this work we correlated transmission spectra of GaN layers grown on sapphire substrates by hydride vapour phase epitaxy with biaxial stress measured in the layers. It was observed that the sign of stress in the GaN layer is changed by Si doping and growth conditions. Transmission curves are shifted relative to each other depending on the stress in the layer. The cut-off wavelength of the transmission curves has a tendency to shift near parallel to a shorter wavelength range when the GaN layer is under the compression biaxial stress. When the GaN layer is under the tensile biaxial stress the cut off wavelength has a tendency to shift near parallel to a longer wavelength range).

Hydride Vapor Phase Epitaxy (HVPE) was used to grow 1-4 μm thick undoped GaN layers on 4H-SiC and sapphire substrates. To adjust mechanical strain and crack formation in the GaN/SiC samples, the AlGaN-based buffer layer was grown at low temperature (920-980°C) and the GaN layer was grown at a higher temperature (1000-1040°C). Laser scribing through the GaN layer or the SiC substrate was applied to fabricate dies from the GaN/SiC and GaN/sapphire samples. The laser irradiation passing through the GaN layer to the sapphire substrate or through the SiC substrate to the GaN layer, along two orthogonal directions created a net of micro-cavities in sapphire and melted grooves in SiC that promote easy breakage of the sample into rectangular dies.

A comparative study of the degradation of HVPE-grown 360 nm AlGaN/GaN UV and commercially available InGaN/GaN blue LED chips was performed. The common feature of the degradation of these two types of LEDs was found to be the increase of the conductivity of shunt paths under current injection. The paths (shunts) are localized in the extended defects system (EDS). It is proposed that the conductivity increase is due to defect formation under multiphonon carriers recombination in a part of the EDS enriched by Ga or In atoms. This process is accompanied by a local overheating and migration of Ga or In atoms. To increase the lifetime of the AlGaN/GaN UV LEDs to more than 2000 h it is necessary to improve their nano-structural and nanoscale AlGaN composition ordering. (c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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.

Some results on the creation of ultraviolet light-emitting diodes based on GaN/AlGaN heterostructures grown on aluminum nitride (AlN) substrates using the method of chloride-hydride epitaxy are presented. The peak wavelengths lie within the range of 360–365 nm, the width of a spectral curve is 10–13 nm, and the output optical power of light-emitting diode chips is 50 mW at a current of 350 mA.

We report on results of the performance study of UVA LEDs depending on the thickness of the active region. UVA LEDs are based on GaN/AlGaN heterostructures grown on Al2O3 (0001) substrates by hydride vapor phase epitaxy (HVPE). It is shown that the use of thick (similar to 100 nm) single layer as the active region of UVA LED is a promising concept to achieve enhanced efficiency. (c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this paper, we report on growth of ultraviolet light-emitting diode (UV LED) heterostructures by hydride vapour phase epitaxy (HVPE) on sapphire substrates and results of the heterostructures characterization by X-ray diffractometry, scanning electron microscopy, photo- and electroluminescence, micro-photoluminescence, collected from the cleaved edges and the surface of the heterostructure with lateral resolution of about 1 mu m. The heterostructures demonstrate efficient hole injection and low droop of the external quantum efficiency. Packaged 360 nm UV LED chips have wall-plug efficiency of 1-1.5 %. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We report on results of the performance study of UVA LEDs depending on the thickness of the active region. UVA LEDs are based on GaN/AlGaN heterostructures grown on Al2O3 (0001) substrates by hydride vapor phase epitaxy (HVPE). It is shown that the use of thick (-100 nm) single layer as the active region of UVA LED is a promising concept to achieve enhanced efficiency.

The results of work on developing and studying ultraviolet (UV) light-emitting diodes (LEDs) based on GaN/AlGaN heterostructures fabricated on Al 2 O 3 (0001) substrates by the chloride-hydride vaporphase epitaxy are presented. The maximum in the electroluminescence spectrum is located in the wavelength range of 360–365 nm, and its full width at half maximum is 10–13 nm. At a working current of 20 mA, the optical density and efficiency of the UV LED are 1.14 mW and 1.46%, respectively.