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.

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.

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.

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.

High Electron Mobility Transistor (HEMT) heterostructures based on III-N sem-iconductors (nitrides of Al and Ga) have become increasingly widespread in recent years. They are used in the manufacture of microwave transistors, high-power transistors for power elec-tronics, etc. However, mass application of such transistors requires a reduction in the cost of heterostructures due to the use of cheap substrates and an increase in the area of one substrate. Thus, substrates of single-crystal Si(111) are of great interest. They are available in diameters up to 300 mm, and the possibility of growing III-N structures has already been demonstrated for them. Nevertheless, the epitaxy of III-N HEMT structures on Si substrates is complicated due to a number of technological difficulties in the epitaxy of such structures. In this paper, the dynamics of curvature and residual bow of III-N HEMT structures were experimentally studied during epitaxy and after cooling for Si(111) substrates with a diameter of 100 mm and various thicknesses of substrates and grown semiconductor films. It has been shown that the technology developing and optimization should be carried out on thin substrates, while device structures should be grown on thick substrates. Furthermore, the mechanical stresses can be controlled accurately enough so after epitaxy the bow of the structure is minimal.

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.

The influence of n-type doping of the AlGaN barrier layer in AlGaN/AlN/GaN single-and triple-channel heterostructures on their electrical properties was studied. It was found that the optimal thickness of i-AlGaN spacer is 3 nm, and the Si concentration in n-AlGaN is 7 center dot 10(18) cm(-3). The lowest predicted sheet resistance at room temperature for the triple-channel structure of the optimal design is similar to 90 omega sq(-1), three times lower than that of the-channel structure.

Reflection spectra from a resonant Bragg structure with 30 GaN/AlGaN quantum wells have been measured at room temperature. Numerical modeling using the method of transfer matrices gave a quantitatively accurate fit of the experimental results. Defined radiative and non-radiative broadening parameters of the exciton in GaN/AlGaN quantum wells.

В докладе показаны актуальные результаты разработки отечественной технологии выращивания гетероструктур на основе нитрида галлия (GaN) на сверхвысокоомных эпитаксиальных структурах кремния диаметром 150 мм. Получены структуры Ga(Al)N/Si диаметром до 150 мм с подвижностью электронов в 2DEG более 1500 см2В-1с-1, изготовлены тестовые транзисторы GaN HEMT с напряжением отсечки порядка -6,5 В, максимальным током стока насыщения 570 мА/мм, крутизной транзисторов не менее 100 мСм/мм и пробивным напряжением более 200 В.

A genetic algorithm was employed to optimize the Si doping profile of lumines-cence InGaN-based heterostructures. It was shown that, in the optimized structure, a 'para-sitic' luminescence from GaN barrier layers could be suppressed while the efficiency remained the same as that of the best uniformly doped structure. Moreover, the optimized structure had a 2.6 times lower total Si concentration, which could be beneficial in terms of crystal quality of the grown layers.

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.

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.

С использованием отечественной установки МОС-гидридной эпитаксии Dragon-125 разработана технология выращивания НЕМТ-структур на основе AlGaN и InAlN с намеренно легированными изолирующими буферными слоями и in-situ Si3N4-покрытиями. Изготовлены НЕМТ-транзисторы и измерены их параметры.

The influence of dislocations on luminescence of InGaN/GaN multiple quantum wells was investigated by temperature-dependent and time-resolved room-temperature photoluminescence measurements and analyzed via localized-state ensemble model. The results show that dislocations decrease non-radiative recombination time and do not affect either radiative recombination time or non-radiative recombination mechanism. Moreover, dislocation-related broadening, increasing linearly with increased dislocation density, was found to take place. However, a significant part of spectral width (∼55 meV) is not defined by either dislocation-induced or alloy- and thermally-induced broadening, revealing the existence of other broadening mechanisms (e.g. carrier–carrier scattering-induced broadening).

Optical properties of a structure with a periodic system of 100 InGaN quantum wells (QWs) separated by non-tunneling GaN barriers have been investigated at room temperature. The structure periodicity corresponded to the Bragg diffraction condition at the frequency of the QW excitons. Numerical modeling using transfer matrices gave a quantitatively accurate fit of the experimental results. The model included the resonance response of A, B, and C excitons in QWs and an optical absorption tail in the barriers and buffer layer. We have determined the radiative and non-radiative broadening of the excitons in the InGaN QWs.

Представлены состав, описание основных узлов и принцип работы экспериментального образца установки «Эпифаз ТМ 200-01» газофазной эпитаксии из металлоорганических соединений (ГФЭ МОС) для роста III-N-гетероструктур на подложках диаметром до 200 мм

Growth of GaN layers by MOVPE on sapphire substrates at various pressures, including above atmospheric, was studied. It is shown that epitaxy at higher pressures does not change the crystal perfection of the layers, the electron mobility, and the impurities incorporation, but leads to the formation of a surface with a smaller lateral scale of inhomogeneities. The epitaxy pressure also affects the ratio of the intensity of the band-edge and impurity-related lines in the photoluminescence spectra and the leakage currents in the reverse-biased Schottky barrier.

Продемонстрированы новые результаты разработки отечественной технологии Ga(Al)N-on-Si. Разработка ведется АО «Эпиэл» в тесном сотрудничестве с НТЦ микроэлектроники РАН. Получены первые отечественные гетероэпитаксиальные структуры Ga(Al)N/Si диаметром 100 мм для HEMT-транзисторов с подвижностью электронов в канале 2DEG выше 1500 см2В-1с-1, выращенные на сверхвысокоомных эпитаксиальных структурах Si на МОГФЭ-системе Dragon-125, разработанной в НТЦ микроэлектроники РАН.

Si3N4 deposition from silane and ammonia in a number of III-N MOVPE reactors of various sizes was studied in a wide range of reactor conditions. It was revealed that Si3N4 deposition rate depends on temperature, pressure, carrier gas type, and ammonia concentration. Deposition rate rises with temperature up to 1050-1100 degrees C in a manner typical for temperature-activated processes, but under any studied conditions, including the 800-850 degrees C range, it is strictly linear with SiH4 concentration indicating the absence of high-order parasitic reactions at high temperature and surface passivation at low temperature. For a low-volume reactor the higher the pressure is, the faster the deposition is both for N-2 and H-2 carrier gases. For large reactors the dependence is non-monotonic. At temperature above 900 degrees C using H-2 as a carrier gas results in a higher Si3N4 deposition rate than when using N-2. If nitrogen is used as a carrier gas, deposition rate gradually rises with ammonia concentration. If hydrogen is used, deposition rate rapidly rises with ammonia concentration and then gradually falls. If hydrogen-nitrogen mixture is used as a carrier gas, deposition rate changes in a linear manner with the mole fraction of hydrogen in the carrier gas.

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.