The results of the study of the influence of Fe segregation into the unintentionally doped GaN channel layer in AlGaN/AlN/GaN heterostructures with Fe-doped GaN buffer layer on the electrical properties of two-dimensional electron gas are presented. A set of several samples was grown by metal-organic vapor-phase epitaxy and characterized by the van der Pauw method. The dependence of concentration and mobility of the two-dimensional electron gas on the channel layer thickness was analyzed theoretically by self-consistent solving of 1D Poisson and Schrödinger equations and scattering rate calculations within the momentum relaxation time approximation. It was found that both concentration and mobility decreases were responsible for the increase in the sheet resistance in the structures with a thinner channel layer, with a drop in mobility being not only due to ionized impurity scattering, but also due to a combined effect of weakening of screening, lower carrier energy and change in form-factors on scattering by interface roughness, dislocations and polar optical phonons.

This study numerically optimizes Cu₂ZnSnS₄ (CZTS)/Cu(In,Ga)Se₂ (CIGS) tandem solar cells (TSCs) with a ZnS buffer layer using Silvaco-Atlas software, achieving a record simulated efficiency of 29.41% (AM1.5 G), a 4.14% improvement over the baseline (25.27%). Critical loss mechanisms are addressed through systematic parameter optimization: a CZTS absorber thickness of 0.18 μm balances photon absorption and transmission, while a doping density of 3 × 10¹⁶ cm⁻³ minimizes recombination losses by optimizing the depletion width. Comprehensive loss analysis reveals that excessive CZTS thickness (>0.18 μm) obstructs low-energy photons from reaching the CIGS subcell, while overdoping (> 3 × 10¹⁶ cm⁻³) narrows the depletion region, elevating recombination. Temperature-dependent simulations (260–380 K) demonstrate a 12.83% efficiency decline at 380 K, driven by bandgap narrowing (Varshni’s Effect) and increased recombination. This work resolves critical challenges in optical losses and thermal instability, providing a roadmap for eco-friendly, high-efficiency tandem photovoltaics.

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

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.

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.