The properties of graphene chips with low reproducibility (LR) after photolithography (PLG) and graphene functionalization have been studied. It is shown that the introduction of additional cleaning after PLG can significantly increase the reproducibility of the parameters of processed graphene in biosensors. The use of dilute PBS solutions for virus detection makes it possible to increase the relative concentration sensitivity of biosensors by several times.

The well-known effect of the local interaction between graphene and photoresist (LIGF) during the creation of biosensors is shown to lead to non-uniform distribution of compressive stresses, which deteriorates the adsorption properties of graphene, parameter reproducibility, and detecting ability of influenza B and SARS-Cov-2 biosensors. It is also shown that controlling the occurrence of LIGF areas on a graphene surface by atomic force microscopy or introducing a protective layer between graphene and photoresist can minimize the non-persistent effect of LIGF. The results of influenza B and SARS-CoV-2 imaging on the graphene surface in biosensor chips in a scanning electron microscope are presented.

To analyze the modification of the functionalized surface of graphene by protein molecules, a chemiluminescent enzyme-linked immunosorbent assay based method was proposed. Using the example of functionalized graphene (FG) purification, the possibilities of chemiluminescent control of the state of its surface are shown. Methods for purifying FG from protein molecules with the restoration of the ability to resorb protein molecules are discussed. It has been shown that the FG surface can be cleaned from sorbed proteins, and a biosensor can be designed again based on such purified graphene, including with a different specificity. Therefore, the graphene sensor can be used repeatedly. Keywords: functionalized graphene, 1-pyrenemethylamine hydrochloride, cyclic voltammetry, chemiluminescence, monoclonal antibodies, biosensors

The well-known effect of the local interaction between graphene and photoresist (LIGF) during the creation of biosensors is shown to lead to non-uniform distribution of compressive stresses, which deteriorates the adsorption properties of graphene, parameter reproducibility, and detecting ability of influenza B and SARS-Cov-2 biosensors. It is also shown that controlling the occurrence of LIGF areas on a graphene surface by atomic force microscopy or introducing a protective layer between graphene and photoresist can minimize the non-persistent effect of LIGF. The results of influenza B and SARS-CoV-2 imaging on the graphene surface in biosensor chips in a scanning electron microscope are presented.

To analyze the modification of the functionalized surface of graphene by protein molecules, a chemiluminescent enzyme immunoassay method was proposed. Using the example of functionalized graphene (FG) purification, the possibilities of chemiluminescent control of the state of its surface are shown. Methods for purifying FG from protein molecules with the restoration of the ability to resorb protein molecules are discussed. It has been shown that the FG surface can be cleaned from sorbed proteins, and a biosensor can be designed again based on such purified graphene, including with a different specificity. Therefore, the graphene sensor can be used repeatedly.

In this work, the modification of the surface parameters of graphene chips after electrolysis treatment in a NaClO 4 aqueous solution has been studied. Two electrolysis modes have been analysed. In the first one, a negative potential (-0.2 V) is applied to the graphene chips, while in the second one the potential is positive (0.8 V). Investigation using a number of techniques including atomic force microscopy, Kelvin probe force microscopy, Raman spectroscopy, measurements of current-voltage characteristics and low-frequency noise has shown that the electrolysis mode with application of a positive potential on graphene chips decreases the 1/ f noise and allows one to obtain a uniform surface potential distribution while leaving the graphene structure undamaged. The results of this study help to understand the efficiency and reproducibility of the procedure for electrolysis treatment of graphene chips.

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.

Graphene is considered as a promising candidate for manufacturing of sensors due to its extreme sensitivity to molecule absorption. In this work, we show the connection between the electrical and optical properties of epitaxial graphene chips grown on 4 H -SiC and intended for the production of protein-based sensors. Using of a complex of techniques, including Raman spectroscopy, atomic force microscopy, Kelvin probe microscopy, study of I-V characteristics and low-frequency noise, it is shown that the character of frequency dependence of the spectral density of voltage fluctuations and its value at a frequency of 1 Hz can be used for classification and selection of graphene chips for their application as sensors. Classification of the graphene chips will allow more efficient development of graphene-based biosensors.

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.

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).

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 (-100 nm) single layer as the active region of UVA LED is a promising concept to achieve enhanced efficiency.

Using synchrotron X-ray topography and phase-contrast imaging, we investigated lattice defects in bulk SiC crystals grown by physical vapor transport in a free spreading condition. We find that polytype inclusions appearing at initial growth stage are overgrown by the matrix, making pores which are then transformed into micropipes with a low density of 10 cm−2, in particular, in the lateral region. We propose that complex planar defects configured from dislocations and micropipes are transformed into slit pores via vacancy-diffusion and micropipes-attraction mechanisms. Our finding suggests that suppression of the nucleation of foreign polytype inclusions is a key approach for providing high quality free spreading SiC growth.

Final stage of the degradation of the external quantum efficiency of AlGaN/GaN UV light-emitting diodes (LEDs), grown by chloride-hydride vapor-phase epitaxy, and high-power InGaN/GaN blue LEDs, produced by metal-organic vapor-phase epitaxy, has been comparatively studied. It is shown that one of these processes leading to a decrease in the quantum efficiency for both types of LEDs is the local defect formation involving the Gold-Weisberg mechanism in a system of extended defects. To prolong the service life of AlGaN/GaN UV LEDs to more than 2000 h, it is necessary to improve the nanostructural arrangement of the material of light-emitting structures and determine the contribution from the AlGaN composition disorder to the degradation of the external quantum 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.

The growth kinetics of SiC crystals doped with Al and Ga impurities and grown by the sublimation sandwich method at a small spacing between the source and the seed (<1 mm) has been studied. Dependence of an Al-doped SiC crystals growth rate on the clearance is shown to be non-monotonic and exhibits maximum at the clearance about of 100-300 μm. Such dependence is also observed for growth of pure and Ga-doped SiC crystals but only on (0001)Si face. The derived dependencies suggest that there are some considerable kinetic limitations of the SiC growth rate. High quality SiC crystals with such high concentration of the Al impurity as 2x1021 cm-3 were grown.

In this paper we report on dependence of the temperature of active layers (ALs) of heterostructures of light-emitting diodes (LEDs) based on AlGaN (UV LEDs) and InGaN (blue LEDs) on various current values (up to 150 m.). It is shown that the heating of the heterostructures is directly related to the concentration of defects. UV LEDs are characterized by a higher temperature than blue LEDs, they also demonstrate a lower wall-plug efficiency (WPE) (about 1.5% at 20 mA). The WPE of blue LEDs with and without the superlattice are 15% and 18%, respectively. To verify the accuracy of the performed measurements the theoretical calculation of the AL temperature according to Van Roosbroeck-Shockley theory and the model of 2D-combined density of states is carried out.

In this paper we report on results of development of ultraviolet light-emitting diodes (UV LEDs) based on GaN/AlGaN heterostructures grown on Al2O3 (0001) substrates by chloride-hydride vapour phase epitaxy (CHVPE). Both UV LED heterostructures and packaged dies are investigated. UV LEDs proved performance capability at current density up to 125 A/cm(2) and revealed wall-plug efficiency (WPE) of 1.5% at operating current of 20 mA.