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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.).

The paper presents the derivation of a model for minority carriers collection based on the reciprocity theorem and its application for determination of hole diffusion length in n-GaN by means of photoluminescence. The estimated hole diffusion lengths at room temperature are 110 nm and 194 nm in the case of low and high excitation, respectively, which could be explained by saturation of non-radiative recombination centers in bulk GaN and at the surface with photogenerated carriers.

The influence of two types of AlN/GaN interfacial non-idealities, namely unintentional Ga incorporation into AlN spacer and blurring of the spacer due to Al and/or Ga atomic diffusion on the mobility and density of two-dimensional electron gas in AlGaN/AlN/GaN heterostructure was studied theoretically. It was found that moderate amount of GaN in the nominal AlN spacer does not affect much the mobility and density of 2DEG as long as the interface is abrupt. In contrast, the blurring of AlN/GaN interface was found to have a significant impact on the mobility and sheet resistance of the structure since the GaN channel actually becomes AlGaN and alloy-disorder scattering takes place.

Temperature-dependent luminescent properties of dual-wavelength blue-cyan light emitting diodes (LEDs) based on InGaN quantum wells were investigated by means of photo- (PL) and electroluminescence (EL) spectroscopy techniques. The results showed that the thickness of the interwell GaN layer had a great impact on the spectra (especially on the EL ones) at room temperature. At low temperatures, however, the EL spectra are nearly identical for all the samples regardless the differences at room temperature. The differences in the temperature behavior of the above-bandgap PL spectra can be explained in terms of different areas of carrier collection region for the samples with different interwell barrier thickness, as evidenced by the below-bandgap PL spectra measurements as well as by the Beer's law calculations. Additionally, an anomalous increase of the above-bandgap PL intensity is observed at the temperature range of ~120–150 K, which is absent in the case of below-bandgap excitation.

Emission of terahertz radiation from a AlGaN/GaN/Al $_{\mathbf {2}} \mathbf {O} _{\mathbf {3\, }}$ heterostructure with a surface metal grating is investigated under conditions of 2D electron heating in a lateral electric field. The studies are performed under essentially nonequilibrium conditions when the effective temperatures of 2D electrons and 2D plasmons are several times higher than the lattice temperature. This makes it possible to observe and explore high-quality peaks of intense THz radiation corresponding to 2D plasmon resonance.

High electron mobility transistors (HEMTs) technologies based on AlGaN/GaN and InAlN/GaN heterostructures have been developed. The research focused on influence of epitaxial growth conditions and buffer doping profiles on electrical properties HEMTs. An output power density of 4W/mm at 17 GHz was demonstrated for InAlN/GaN HEMTs and 7W/mm at 10 GHz for AlGaN/GaN HEMTs.

The effect of the Fe doping profile of the GaN buffer layer in the heterostructures for high-electron mobility transistors was studied experimentally and by computer simulation. The exponential Fe tail extending to the nominally undoped layers may greatly affect the properties of the structure. Reducing the distance between the channel and the Fe-doped buffer to less than 1 μm results in a decrease in the density and mobility of the two-dimensional electron gas. It also leads to the higher off-state avalanche breakdown voltage and reduced leakage current. A good agreement between simulation and experimental data is obtained when taking into account a Fe segregation effect, while an abrupt doping profile lead to significant discrepancies between them

We report on studies of electrically excited non-equilibrium 2D electrons and 2D plasmons in an AlGaN/GaN nanostructure. Optical access to 2D plasmons is provided by means of a metal grating fabricated at the nanostructure surface, while the properties of 2D electrons are examined in the samples without metal grating. The paper focuses on the creation of highly non-equilibrium conditions when the effective temperature of 2D electrons is much higher than the crystal lattice temperature. Such conditions are realized by applying short electrical pulses with a low repetition frequency. A method has been developed for independently determining the temperature of hot electrons and the temperature of the crystal lattice under an applied electric field. It has been shown that under highly non-equilibrium conditions the spectral density of terahertz electroluminescence of 2D plasmons can significantly exceed that of 2D electrons at a certain frequency.

Simulation analysis of III-N two-dimensional electron gas-based structures that could be used for stable monolithically integrated enhancement/depletion-mode circuits was carried out. Three different designs were proposed and analysed, including a novel p-GaN/AlN-GaN SPSL/GaN, which is expected to have lower ON-state resistance and higher transconductance than conventional normally-off GaN-based transistors.

Terahertz radiation emission from an electrically excited AlGaN/GaN heterostructure with a surface metal grating was studied under conditions of two-dimensional (2D) electron heating by the lateral electric field. Intensive peaks related to nonequilibrium 2D plasmons were revealed in the terahertz emission spectra with up to 4 times selective amplification of the radiation emission in the vicinity of 2D plasmon resonance. This selective emission was shown to be frequency-controllable by the grating period. Exact spectral positions of the 2D plasmon resonances were preliminarily experimentally detected with the help of equilibrium transmission spectra measured at various temperatures. The resonance positions are in a satisfactory agreement with the results of theoretical simulation of the transmission spectra performed using a rigorous solution of Maxwell’s equations. The effective temperature of hot 2D electrons was determined by means of I– V characteristics and their analysis using the power balance equation. It was shown that for a given electric field, the effective temperature of nonequilibrium 2D plasmons is close to the hot 2D electron temperature. The work may have applications in GaN-based electrically pumped emitters of terahertz radiation.Terahertz radiation emission from an electrically excited AlGaN/GaN heterostructure with a surface metal grating was studied under conditions of two-dimensional (2D) electron heating by the lateral electric field. Intensive peaks related to nonequilibrium 2D plasmons were revealed in the terahertz emission spectra with up to 4 times selective amplification of the radiation emission in the vicinity of 2D plasmon resonance. This selective emission was shown to be frequency-controllable by the grating period. Exact spectral positions of the 2D plasmon resonances were preliminarily experimentally detected with the help of equilibrium transmission spectra measured at various temperatures. The resonance positions are in a satisfactory agreement with the results of theoretical simulation of the transmission spectra performed using a rigorous solution of Maxwell’s equations. The effective temperature of hot 2D electrons was determined by means of I– V characteristics and their analysis using the power balance ...

Calculational analysis of different scattering mechanisms of two-dimensional electron gas in AlGaN/(AlN)/GaN and InAlN/(AlN)/GaN high-electron mobility transistors was carried out. It was found that the mobility of AlGaN-based structures at room temperature is mainly limited by inherent scattering mechanisms (namely, optical and acoustic phonon scattering), while the mobility in our InAlN-based structures is limited by the interface roughness scattering. The low-temperature mobility is found to be limited by the interface roughness scattering for both AlGaN- and InAlN-based structures.

Dependence of electroluminescence spectrum shape of blue-cyan InGaN-based dichromatic double quantum well light emitting diodes on the thickness and doping level of the barrier between quantum wells was investigated numerically and experimentally.

Optical and structural properties of thick InGaN layers grown by MOCVD and MBE were studied by photoluminescence, optical transmission and Raman spectroscopies and X-ray diffraction analysis. Optical bandgap, Urbach energy, and full widths at half maximum (FWHM) of photoluminescence and Raman spectra depending on the InGaN alloy composition were determined experimentally. Minimal theoretical linewidth of photoluminescence spectra resulted from random distribution of In and Ga atoms in cation sublattice was calculated.

The series of InAlGaN LED structures containing two different quantum wells emitting at wavelengths of ~ 430 nm and ~ 490 nm was grown. The influence of the quantum wells order, thickness of the barrier between the wells and its doping level on the optical properties was studied by photo- and electro-luminescence measurements. It was found that the quantum well with longer-wavelength emission is preferable to be located farther from a player than the shorter-wavelength quantum well to obtain emission from both QWs. Variation of the thickness of the barrier between the QWs and its doping level allows controlling the intensity ratio of two emission peaks.