Search

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 studied an effect of spatial disorder on the optical response of resonant Bragg structures with InGaN quantum wells. Using an experimentally verified model, we calculated a transformation of the optical reflection from the resonant Bragg structures with 60, 100, and 200 quantum wells as a function of the degree of disorder in the system. A critical threshold deviation from the exact periodicity was revealed, which causes a qualitative change of the optical resonance. [ABSTRACT FROM AUTHOR]

Room-temperature reflectance spectra are recorded for a resonant Bragg structure with 30 GaN/AlGaN quantum wells. Accurate quantitative fitting of the experimental results is achieve by means of transfer matrix numerical modeling. Parameters of radiative and nonradiative exciton broadening in the GaN/AlGaN quantum wells are determined. [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 effect of the growth temperature and the flow of trimethylgallium on the process of selective epitaxy of gallium nitride in windows of submicron size have been studied. The conditions under which homogeneous nucleation and coalescence of nuclei are combined with a low growth rate are determined. The steady growth of variously oriented gallium nitride strips with a height of 50 nm and a width of 600 nm was realized. [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: The selective epitaxial growth of GaN by metalorganic vapor-phase epitaxy combined with ion-beam etching is investigated. To this end, partially masked GaN epitaxial layers are fabricated by depositing a thin Si3N4 layer onto the surface in a single technological process with the growth of GaN and the subsequent opening of windows of different shapes in this layer by an ion beam. Selective epitaxial growth regimes are studied. It is shown that, in a situation where the total area of the windows in the mask is small relative to the total area of the sample, the required epitaxy duration should be 5-10 s, which impairs the reproducibility of the parameters of the epitaxial process. It is also shown that the mechanism of the selective growth of submicrometer objects differs significantly from that for planar layers and selectively grown layers with dimensions of ~1 μm or greater. The effect of precursor (trimethylgallium and ammonia) fluxes on the character of selective epitaxy is examined. To investigate the possibilities of varying mask topology for fabricating model objects with regard to photonic crystals, the impact of the shape and orientation of the windows in the Si3N4 mask on the character of selective epitaxy is studied. [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]

We demonstrate a resonant Bragg structure formed by quasi-two-dimensional excitons in periodic systems of InGaN quantum wells (QWs) separated by GaN barriers. When the Bragg resonance and exciton–polariton resonance are tuned to each other, the medium exhibits an exciton-mediated resonantly enhanced optical Bragg reflection. The enhancement factor appeared to be largest for the system of 60 QWs. Owing to a high binding energy and oscillator strength of the excitons in InGaN QWs, the resonant enhancement was achieved at room temperature. The samples were grown by the metal–organic vapor-phase epitaxy (MOVPE) on GaN-on-sapphire templates. The most important technological problem of the developed structures is inhomogeneous broadening of the excitonic states due to nonuniform chemical composition of the QWs driven by InN–GaN phase separation trend. We addressed this problem by variation of the vapor pressure, growth rate, growth interactions, and admixing of hydrogen during the MOVPE. The lowest width of 74 meV at room temperature and 41 meV at 77 K was achieved for the excitonic emission line from a single InGaN QW. [ABSTRACT FROM PUBLISHER]

Optical and light-emitting diode structures with an active InGaN region containing short-period InGaN/GaN superlattices are studied. It is shown that short-period superlattices are thin two-dimensional layers with a relatively low In content that contain inclusions with a high In content 1–3 nm thick. Inclusions manifest themselves from the point of view of optical properties as a nonuniform array of quantum dots involved in a residual quantum well. The use of short-period superlattices in light-emitting diode structures allows one to decrease the concentration of nonradiative centers, as well as to increase the injection of carriers in the active region due to an increase in the effective height of the AlGaN barrier, which in general leads to an increase in the quantum efficiency of light-emitting diodes. [ABSTRACT FROM AUTHOR]

A new approach to development of effective monolithic white-light emitters is described based on using a short-period InGaN/GaN superlattice as a barrier layer in the active region of LED structures between InGaN quantum wells emitting in the blue and yellow-green spectral ranges. The optical properties of structures of this kind have been studied, and it is demonstrated that the use of such a superlattice makes it possible to obtain effective emission from the active region. [ABSTRACT FROM AUTHOR]

The structural and optical properties of light-emitting diode structures with an active region based on ultrathin InGaN quantum wells limited by short-period InGaN/GaN superlattices from both sides have been investigated. The dependences of the external quantum efficiency on the active region design are analyzed. It is shown that the use of InGaN/GaN structures as limiting graded-gap short-period superlattices may significantly increase the quantum efficiency. [ABSTRACT FROM AUTHOR]

Effect of pressure in the reactor in the case of growth of active regions in the InGaN/GaN light-emitting diodes by the method of vapor-phase epitaxy from metalorganic compounds on their electroluminescent and structural properties has been studied. It is shown that, as pressure is increased, the InGaN layers become transformed from being continuous in the lateral direction to the layers of separate InGaN islands. This transformation affects both the emission efficiency and the dependence of efficiency on current. [ABSTRACT FROM AUTHOR]

A new method of forming InGaN/GaN nanostructures emitting in the long-wavelength green spectral range is proposed and implemented. The method is based on growing a thin InGaN layer over nanosized pits formed in situ by etching a locally AlN-masked GaN layer in a hydrogen-containing atmosphere. [ABSTRACT FROM AUTHOR]

Magnesium is the only acceptor impurity practically used in MOCVD of GaN. High activation energy requires high impurity concentration, which results in epilayer morphology degradation. In the presented paper an influence of growth regimes, including choice of carrier gas, on GaN:Mg morphology is presented. It is demonstrated that surface morphology depends on an average magnesium concentration and strongly improves with using nitrogen as carrier gas. [ABSTRACT FROM AUTHOR]

Processes of active-region formation for green LEDs on the basis of multilayer strained InGaN/GaN nanoheterostructures have been studied. It is shown that the formation of structures of this kind is highly affected by elastic stress relaxation leading to a larger amount of indium incorporated into InGaN layers. For structures emitting in the blue spectral range, an increase in the number of quantum wells (QWs) from 1 to 10 does not lead to stress relaxation or to a shift of the emission wavelength, whereas for structures emitting in the green spectral range, raising the number of QWs from one to five causes a monotonic increase in the emission wavelength. [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]