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InGaN-based monolithic multi-color light emitting diodes (LEDs) are studied both experimentally and theoretically with the focus on factors controlling their emission spectra and efficiency. A number of LEDs with different designs of spacers separating active regions providing blue and green light emission is examined. Unexpected behavior of the multi-color LED efficiency is explained in terms of a simple balance model, assuming some degradation of materials quality of the green active region grown on top of the blue one. Electrical properties of spacers separating different active regions in the multi-color LED structures are identified as the major factor controlling the contributions of these active regions to the total emission spectrum. Correlations between the type and level of the spacer doping and the emission spectrum are found by simulations. Alternative ways of the spectral control by using polarization doping in the graded-composition InGaN and AlGaN alloys used as the spacers are suggested. Color characteristics of blue/green dual-wavelength LEDs are also measured and discussed, regarding their possible applications. [ABSTRACT FROM AUTHOR]

In this paper we obtained GaN and InGaN nanowires on AlN/Si (111) templates via pulsed Metal Organic Chemical Vapour Deposition (MOCVD). The growth modes were investigated, in which selective growth is possible. The impact of NH3 flow and TMG flow and exposure time were investigated. Also the possibility of using indium catalyst was studied. It was shown that In can be used in Au-In melt and as self-suffisient catalyst. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The N-Al0.27Ga0.73N/GaN High Electron Mobility Transistors (HEMTs) with different gate lengths L g (ranging from 170 nm to 0.5 μm) and gate widths W s (ranging from 100 to 1200 μm) have been studied. The S parameters have been measured; these parameters have been used to determine the current-gain cutoff frequency f t, the maximum oscillation frequency fmax, and the power gain MSG/MAG and Mason’s coefficients were investigated in the frequency range from 10 MHz to 67 GHz in relation to the gate length and gate width. It was found that the frequencies f t and fmax attain their maximum values of f t = 48 GHz and fmax = 100 GHz at L g = 170 nm and W g = 100 μm. The optimum values of W g and output power P out of the basic transistors have been determined for different frequencies of operation. It has also been demonstrated that the 170 nm Al0.27Ga0.73N/GaN HEMT technology provides both good frequency characteristics and high breakdown voltages and is very promising for high-frequency applications (up to 40 GHz). [ABSTRACT FROM AUTHOR]

We study the formation of a superradiant optical mode in the room temperature reflection spectra from resonant Bragg structures (RBSs) composed of single and double (In,Ga)N quantum wells (QWs) in the unit cell. The appearance of the mode manifests itself by a significant increase in the resonant optical reflectivity due to the electromagnetic coupling of quasi-two-dimensional excitons in the QWs. The implementation of the supercells with double (In,Ga)N QWs results in an increase in the oscillator strength of the quasi-2D excitons and corresponding rise of the radiative broadening parameter to the value as high as 0.3 ± 0.02 meV. We also show that the supercells with double QWs are preferable for RBS with large number of periods due to better tolerance to deviations from the exact periodicity. [ABSTRACT FROM AUTHOR]

In the present paper we report on the observation and study of intense spontaneous THz emission from modulation-doped AlGaN/GaN heterostructure under conditions of heating of two-dimensional electron gas in lateral electric field. The experimental results are compared with the model of blackbody-like thermal emission of hot 2D electrons. Complementary transport measurements and theoretical simulation were carried out to determine the dependence of effective electron temperature on electric field. The role of non-equilibrium optical phonon accumulation is discussed. [ABSTRACT FROM AUTHOR]

Elastic stresses in AlN layers on silicon substrates of different thickness, as well as in multilayer (Al, Ga)N structures grown on AlN/Si templates, were investigated based on in-situ reflectometry/deflectometry data. It was found that tensile stresses arise during the growth of AlN, with their magnitude increasing with thicker the substrate. During the growth of multilayer step-graded (Al, Ga)N structures, all layers underwent compressive stress which decreased towards the surface. After cooling the structures to room temperature, some of the lower AlGaN layers remained entirely compressed, while another part experienced both compressive (in the lower part of each layer) and tensile (in the upper part of each layer) stresses. [ABSTRACT FROM AUTHOR]

Study of Ga2O3 deposition by MOVPE using trimethylgallium and oxygen was performed in a wide temperature range. It was found that for Ga2O3 deposition rate vs temperature dependence is very close to the TMGa pyrolysis in nitrogen. Kinetically-limited range for these processes corresponds to 550–700°C, that is 150°C higher, then for GaN deposition in the same reactor. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the formation of a superradiant optical mode in the room-temperature reflection spectra from a resonant Bragg structure composed of 30 equidistant GaN quantum wells separated by (Al,Ga)N barriers. The mode arises when the condition of the Bragg diffraction is fulfilled at the wavelength corresponding to the energy of the quasi-two-dimensional excitons in the quantum wells. It manifests itself as a significant increase in the amplitude and a change in the shape of the resonant optical reflection due to the electromagnetic coupling of the excitons. By modeling of the optical spectra, we evaluate the radiative and non-radiative broadening parameters of the excitonic states in the GaN quantum wells, which appear to be 0.4 ± 0.02 and 40 ± 5 meV, correspondingly, for the resonant exciton energy of 3.605 eV. The resonant Bragg structure based on the periodic sequence of the GaN quantum wells demonstrates an efficient coupling of photons and excitons at room temperature, which makes it promising for device applications. [ABSTRACT FROM AUTHOR]

A complex study was performed on a set of AlGaN/GaN high-electron-mobility transistor structures grown by metalorganic vapor phase epitaxy on miscut Si(111) wafers with a highly resistive epitaxial Si layer to investigate the influence of substrate miscut on their properties. The results showed that wafer misorientation had an influence on the strain evolution during the growth and surface morphology, and could have a strong impact on the mobility of 2D electron gas, with a weak optimum at 0.5° miscut angle. A numerical analysis revealed that the interface roughness was a main parameter responsible for the variation in electron mobility. [ABSTRACT FROM AUTHOR]

A technique and technology for manufacturing both LED chips and packaged LEDs from AlInGaN/GaN heterostructures grown on novel SiC/Si substrates synthesized by the method of matched substitution of atoms is described. We have studied the current-voltage characteristics, electroluminescence spectra, and dependence of output power and external quantum efficiency on the current. It is shown that the presence of pores in the SiC/Si substrate, which are naturally formed during its growth, leads to a significant increase in the quantum efficiency of LEDs compared with the quantum efficiency of LEDs fabricated on silicon without a SiC sublayer. [ABSTRACT FROM AUTHOR]

The optical properties of a structure with a periodic system of 100 InGaN quantum wells separated by nontunneling GaN barriers are investigated at room temperature. The structure periodicity corresponds to the Bragg-diffraction condition at the quantum-well exciton frequency. The results of numerical simulation using transfer matrices are in reasonable quantitative agreement with the experimental data. The model includes the resonance response of A, B, and C excitons in the quantum wells and the optical absorption tail in the barrier and buffer layers. The radiative and nonradiative damping rates of excitons in the InGaN quantum wells are determined. [ABSTRACT FROM AUTHOR]

We have studied the growth of GaN layers by the metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates at various reactor pressures, including ones above the atmospheric level. It is established that the epitaxial growth at higher pressures does not affect the crystalline perfection of epilayers, their electron mobility, and background impurity level, but leads to the formation of GaN surface with lower lateral scale of inhomogeneities. In addition, the reactor pressure influences the ratio of edge and impurity lines in the photoluminescence spectra and leakage current level in reversely biased Schottky barriers. [ABSTRACT FROM AUTHOR]

The effect of annealing temperature and time on the luminescence intensity of the InGaN/GaN heterostructure subjected to ion beam etching was studied. We show that annealing at a temperature of 1100°C makes it possible to eliminate the radiation defects in the GaN layers that arise in the etching process with a focused Ga+ ion beam (30 keV). [ABSTRACT FROM AUTHOR]

The broadening of the spectral linewidth of the GaN/InGaN/GaN quantum wells caused by the random distribution of indium and gallium atoms in the cation sublattice was analyzed theoretically. The calculated values of the full width at half maximum of the emission spectra at low temperature are much smaller than the usually observed experimental values, indicating that the emission linewidth of the InGaN quantum wells is mostly determined by other broadening mechanisms (e.g. indium clustering, quantum well width fluctuations, background impurity broadening, etc.). [ABSTRACT FROM AUTHOR]

The morphology and electrical properties of doped semi-insulating gallium nitride (GaN) epilayers have been studied. It was found that doping-induced improvement of the insulating properties of GaN epilayers with increased level of doping with carbon or iron is limited by the accompanying deterioration of surface morphology. The character of impurity-related morphology development is different for the two dopants. It is established that the co-doping with carbon and iron allows planarity of the GaN surface to be retained along with a significant improvement of insulating properties of epilayers. [ABSTRACT FROM AUTHOR]

A new approach for calculating the ion dose spatial distribution of the focused ion beam is proposed. The approach is based on the analysis of the secondary electron microscopy image of the area irradiated by the focused ion beam. [ABSTRACT FROM AUTHOR]

The work presents experimental data of Ga+ focused ion beam etching of disc and ring patterns in Si3N4/GaN structure. The reasons for the difference in etching depth between the discs and the rings are described. [ABSTRACT FROM AUTHOR]

Abstract: InAlN/AlN/GaN semiconductor heterostructures with a barrier thickness of 5-13 nm have been grown by metalorganic vapor phase epitaxy (MOVPE) on sapphire and SiC substrates. Optimization of GaN buffer and InAlN layers allows fabricating structures with sheet conductivity values below 210 Ohm/sq. High electron mobility transistors (HEMTs) fabricated from such structures show drain current value exceeding 1.25 A/mm with maximum transconductance of 450 mS/mm. Use of thin in situ Si3N4 capping allows to fabricate and compare HEMT and MIS-HEMTs. [ABSTRACT FROM AUTHOR]