We report on the investigations of AlGaN/GaN field effect transistors with two lateral Schottky barrier gates on the sides of the two-dimensional electron gas. This kind of 'EdgeFET' allowed us to efficiently control the current flow in the 2DEG conduction channel. Moreover, due to depletion, regions at a certain range of reverse biasing form a nanowire, which is beneficial for the adjustable resonant THz detection. Our studies of DC characteristics and photoresponse in the sub-terahertz frequency confirm the validity of the approach.

The aim of this paper is to give an experimental evidence that point defects (most probably gallium vacancies) induce decomposition of InGaN quantum wells (QWs) at high temperatures. In the experiment performed, we implanted GaN:Si/sapphire substrates with helium ions in order to introduce a high density of point defects. Then, we grew InGaN QWs on such substrates at temperature of 730 °C, what caused elimination of most (but not all) of the implantation-induced point defects expanding the crystal lattice. The InGaN QWs were almost identical to those grown on unimplanted GaN substrates. In the next step of the experiment, we annealed samples grown on unimplanted and implanted GaN at temperatures of 900 °C, 920 °C and 940 °C for half an hour. The samples were examined using Photoluminescence, X-ray Diffraction and Transmission Electron Microscopy. We found out that the decomposition of InGaN QWs started at lower temperatures for the samples grown on the implanted GaN substrates what provides a strong experimental support that point defects play important role in InGaN decomposition at high temperatures.

We report on a design of fin-shaped channel GaN/AlGaN field-effect transistors developed for studying resonant terahertz plasma oscillations. Unlike common two dimensional FinFET transistor design, the gates were deposited only to the sides of the two dimensional electron gas channel, i.e., metal layers were not deposited on the top of the AlGaN. This side gate configuration allowed us to electrically control the conductivity of the channel by changing its width while keeping the carrier density and mobility virtually unchanged. Computer simulations and analytical model describe well the general shape of the characteristics. The side gate control of the channel width of these transistors allowed us to eliminate the so-called oblique plasma wave modes and paves the way towards future terahertz detectors and emitters using high quality factor plasma wave resonances.

The n-type GaN epilayers with low electron density were developed on a native substrate using the metalorganic vapour phase epitaxy method and investigated under pulsed electric fields until material breakdown and optically in the spectrum range from 0.1 THz to 60 THz at two temperatures of 77 K and 300 K. The epilayers demonstrated the low-field electron mobility and density values reaching up to 1021 cm²/V·s and 1.06 × 10¹⁶ cm⁻³ (at 300 K) and 2652 cm²/V·s and 0.21 × 10¹⁶ cm⁻³ (at 77 K), respectively. Maximum injected electric power value till the damage of the GaN epilayer was found to be up to 1.8 GW/cm³ and 5.1 GW/cm³ at 77 K and 300 K, respectively. The results indicate new practical possibilities of the GaN material controlled by an external electric field.

Formation and drift of space-charge domains with velocity of sound were experimentally observed in charge current traces of a high-quality lightly doped GaN semiconductor under pulsed electric fields at room and liquid nitrogen temperatures. A GaN epilayer was developed on an Ammono GaN substrate to achieve the electron density and low-field mobility values of 1.06 × 10¹⁶ cm⁻³ and 1021 cm²/V s (at 300 K) and 0.21 × 10¹⁶ cm⁻³ and 2652 cm²/V s (at 77 K), respectively. The formation of moving space-charge domains was observed only in samples with the lengths of 1 mm and longer arising at the critical electric fields starting from ∼0.4 and ∼0.8 kV/cm at 77 and 300 K, respectively. Basic electron transport parameters were found investigating short samples with the lengths of 65 μm and shorter in a wide range of electric fields up to 150 kV/cm, at which the thermal material breakdown occurred. The critical length of a sample for space-charge domain formation was estimated considering the acoustoelectric effects in analysis of pulsed current–voltage characteristics, thus defining the constraints for the design of GaN-based power electronic devices.