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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 (C20H12O5) in a wide range of its concentrations in a phosphate-buffered saline solution: from 1 × 10–3 to 1 × 104 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. [ABSTRACT FROM AUTHOR]

Structural properties and spatial inhomogeneity of MOCVD-grown Al[sub x]Ga[sub 1-x]N layers on (0001) sapphire substrates were studied. A nonuniform distribution of Al across the epilayer was observed in layers grown at constant flux rates of precursors. The model of compositionally graded layer formation is proposed on the basis of cathodoluminescence and X-ray data. It is established that homogeneous samples can be obtained by increasing the flux rate of trimethylaluminum at the initial stage of epilayer growth compared with that in all further stages. Lowering the growth rate reduces strain in epitaxial Al[sub x]Ga[sub 1-x]N layers. The influence of strain on the luminescence properties of the layers is discussed. [ABSTRACT FROM AUTHOR]

A study was made of the growth regimes of undoped epitaxial GaN layers under various substrate nitriding conditions. It was observed that at a nitriding temperature of ∼ 1000°C films are formed with typical growth characteristics in the form of hexagonal pyramids separated by a smoothed surface. The cathodoluminescence pattern in the pyramids revealed a fine structure in which a region of donor-acceptor recombination could be identified. The formation of acceptor levels in this region was attributed to intrinsic structural defects in the GaN layers with unsaturated (broken) bonds. The presence of a donor-acceptor recombination line in mirrorsmooth epitaxial films may indicate that these films contain this type of structural defect. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

MOCVD-grown heterostructures with one or several In[sub x]Ga[sub 1-x]N layers in a GaN matrix have been studied by transmission electron microscopy. In heterostructures with thick InGaN layers, a noncoherent system of domains with lateral dimensions (∼50 nm) on the order of the layer thickness (∼40 nm) is formed. In the case of ultrathin InGaN inclusions, nanodomains coherent with the GaN matrix are formed. The content of indium in nanodomains, determined by the DALI method, is as high as x ≈ 0.6 or more, substantially exceeding the average In concentration. The density of the nanodomains formed in the structures studied is n ≈ (2-5) x 10[sup 11] cm[sup -2]. In the structures with ultrathin InGaN inclusions, two characteristic nanodomain sizes are observed (3-6 and 8-15 nm). [ABSTRACT FROM AUTHOR]

Deep-level transient spectroscopy was used to study the parameters of deep levels in the band gap of epitaxial n-GaN layers after irradiaton of the Schottky barriers with 1-MeV protons to a dose of 10[sup 12] cm[sup -2]. A deep level EP1 with an activation energy of 0.085 eV was introduced by irradiation into the upper half of the GaN band gap. The introduction rate of the corresponding defect was found to depend on the bias voltage applied to the Schottky barrier during irradiation. [ABSTRACT FROM AUTHOR]

A fractal-percolation system that includes extended defects and random fluctuations in the alloy composition is formed during the growth of device structures based on Group-III nitrides. It is established that the specific features of this system are determined not only by the growth conditions. It is shown that the diversity of the electrical and optical properties of InGaN/GaN LEDs (light-emitting diodes) emitting at wavelengths of 450-460 and 519-530 nm, as well as that of the electrical properties of AlGaN/GaN HEMT (high-electron-mobility transistor) structures, is due to modification of the properties of the fractal-percolation system both during the growth process and under the action of the injection current and irradiation. The influence exerted by these specific features on the service life of light-emitting devices and on the reliability of AlGaN/GaN HEMT structures is discussed. [ABSTRACT FROM AUTHOR]

Blue light-emitting diodes (LEDs) based on InGaN/GaN quantum wells (QWs) with different characters of the system of extended defects (SEDs) threading through the active region have been studied using the current-voltage ( I–U), capacitance-voltage ( C–V), and deep-level transient spectroscopy (DLTS) measurements in the dark and under illumination with white light in a temperature range from 100 to 450 K. The DLTS curves exhibit broad E1 and E2 peaks with amplitudes dependent on the illumination. This behavior can be explained assuming the presence of localized states related to SEDs in the active region of the LED. The LEDs with more developed SEDs are characterized by a greater concentration of donor-type traps, which leads to an increase in the density of free charge carriers in QWs, which screen the electron-hole interaction. This circumstance can be among the factors responsible for a severalfold decrease in the quantum efficiency of such LEDs. [ABSTRACT FROM AUTHOR]

The results of the investigation of low-temperature time-resolved photoluminescence in undoped and Si-doped In[sub 0.2]Ga[sub 0.8]N/GaN structures, which contain 12 quantum wells of width 60 Å separated by barriers of width 60 Å, are reported. The structures were grown by the MOCVD technique on sapphire substrates. The photoluminescence properties observed are explained by the manifestation of two-dimensional donor-acceptor recombination. These properties are the high-energy shift of the peak upon increasing the pumping intensity, a low-energy shift with increasing delay time, and a power law of luminescence decay of the t[sup -γ] type. The estimates of the total binding energy for donor and acceptor centers are given. This energy is 340 and 250 meV for Si-doped and undoped quantum wells, respectively. The role of the mosaic structure, which is typical for Group III hexagonal nitrides, is discussed as a factor favorable for the formation of donoracceptor pairs. [ABSTRACT FROM AUTHOR]

Atomic-force microscopy and photoluminescence were used for studying the nanorelief of a (0001)GaN surface treated in sodium-sulfide solutions. The small-scale surface relief of the layer was shown to be largely smoothed after the sulfide treatment. [ABSTRACT FROM AUTHOR]

InGaN/GaN structures with dense arrays of InGaN nanodomains were grown by metallorganic chemical vapor deposition. Lasing in vertical direction occurs at low temperatures, indicating ultrahigh gains (∼10[sup 5] cm[sup -1]) in the active region. Fabrication of an effective AlGaN/GaN distributed Bragg reflector with reflectivity exceeding 90% enables vertical lasing at room temperature in structures with a bottom distributed Bragg reflector, despite the absence of a well-reflecting upper mirror. The lasing wavelength is 401 nm, and the threshold excitation density is 400 kW/cm². [ABSTRACT FROM AUTHOR]

Possible types of orientational relationships for hexagonal and cubic gallium nitride layers on aluminum-magnesium spinel substrates with various crystallographic orientations have been determined as a result of the theoretical and the experimental studies of this system. Most of the experimental data and the data obtained in the present study are consistent with the theoretical considerations. The causes of some apparent inconsistencies are discussed. [ABSTRACT FROM AUTHOR]

Lasing is discovered in the direction perpendicular to the surface in quantum-size InGaN/GaN multilayer heterostructures grown by vapor-phase epitaxy. At high excitation densities one of the modes in the luminescence spectrum, which is modulated by modes of the Fabry-Pérot cavity formed by the GaN/air and GaN/sapphire-substrate interfaces, is sharply amplified and begins to dominate the spectrum. The dependence of the luminescence intensity on pump density has a clearly expressed threshold character. The threshold excitation density in the vertical direction is 5-6 times greater than the stimulated-emission threshold for observation from an end surface of the structure. The gain coefficient in the active region at the threshold for surface-emitting lasing is estimated as 2 × 10[sup 5] cm[sup -1]. The interaction between the cavity modes and the gain spectrum is detected in the form of displacement (by up to 2.6 nm) of modes on the short-wavelength edge of the luminescence spectrum toward higher photon energies. The characteristic temperature (T[sub 0]) measured in the range from 16 to 120 K is 480 K. At higher temperatures T[sub 0] = 70 K. [ABSTRACT FROM AUTHOR]

The influence of rapid-anneal conditions and subsequent coimplantation of oxygen ions on the photoluminescence of erbium ions implanted with an energy of 1 MeV and dose of 5 × 10[sup 14] cm[sup -2] in MOCVD-grown GaN films is investigated. The erbium photoluminescence intensity at a wavelength ∼1.54 µm increases as the fixed-time (15 s) anneal temperature is raised from 700 °C to 1300 °C. The erbium photoluminescence intensity can be increased by the coimplantation of oxygen ions at anneal temperatures in the indicated range below 900 °C. The transformation of the crystal structure of the samples as a result of erbium-ion implantation and subsequent anneals is investigated by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Room-temperature photoluminescence (PL) has been studied in AlGaN/GaN superlattices and GaN epitaxial layers implanted with 1-MeV erbium at a dose of 3 × 1015cm–2 and annealed in argon. The intensity of PL from Er3+ ions in the superlattices exceeds that for the epitaxial layers at annealing temperatures of 700–1000°C. The strongest difference (by a factor of ∼2.8) in PL intensity between the epitaxial layers and the superlattices and the highest PL intensity for the superlattices are observed upon annealing at 900°C. On raising the annealing temperature to 1050°C, the intensity of the erbium emission from the superlattices decreases substantially. This circumstance may be due to their thermal destruction. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Conditions are investigated for the injection of arsenic into gallium nitride layers grown by metalorganic vapor-phase epitaxy. It is shown that the deposition of GaAs on a GaN surface relieves stresses in the GaN layer. The high-temperature overgrowth of a thin GaAs layer by a GaN layer causes As atoms to diffuse into the GaN, produces a thick, homogeneously doped GaN:As region, and creates a bright band in the photoluminescence spectrum with a maximum at ∼2.5 eV. [ABSTRACT FROM AUTHOR]

The effect of annealing on the optical and structural properties of gallium nitride layers grown by metalorganic chemical vapor deposition and implanted with 0.8 to 2.0-MeV erbium ions at doses of (1-4) x 10[sup 14] cm[sup -2] is investigated. Additional implantation of 0.11 to 0.28-MeV oxygen ions at doses of (1-4) x 10[sup 15] cm[sup -2] is performed on some samples. Measurements of the Rutherford backscattering of protons show that amorphization of the gallium nitride layers does not occur at the erbium implantation doses investigated. The formation of erbium-related luminescence centers which emit at 1.54 µm ends before the defect structure of the implanted layers is restored during a postimplantation anneal in the temperature range 700-1300 °C. [ABSTRACT FROM AUTHOR]

The luminescence properties of a GaN/A1[sub 0.1]Ga[sub 0.9]N double heterostructure grown by vapor-phase deposition from organometallic compounds are studied. When luminescence is observed from the end, the radiation intensity shows a sharply defined threshold dependence on the pump density. The threshold excitation density at T = 77 K was ∼40 kW/cm² and the wavelength of the stimulated emission was λ = 357 nm. The long-wavelength shift of the emission line at high pump densities may be attributed to renormalization of the band gap caused by manyparticle interactions in the electron-hole plasma. [ABSTRACT FROM AUTHOR]

An investigation was made of the electrochemical etching of i-n-GaN light-emitting diode structures in aqueous solutions of KOH and NaOH to remove parasitic low-resistivity layers and inclusions in the structures which shunt the active current flow channels through the structures and lower the electroluminescence intensity. The electroluminescence intensity of the structures increased by two or three orders of magnitude during the etching process. [ABSTRACT FROM AUTHOR]