In this work, we study the thermal degradation of In-rich In x Ga1–x N quantum wells (QWs) and propose explanation of its origin based on the diffusion of metal vacancies. The structural transformation of the In x Ga1–x N QWs is initiated by the formation of small initial voids created due to agglomeration of metal vacancies diffusing from the layers beneath the QW. The presence of voids in the QW relaxes the mismatch stress in the vicinity of the void and drives In atoms to diffuse to the relaxed void surroundings. The void walls enriched in In atoms are prone for thermal decomposition, what leads to a subsequent disintegration of the surrounding lattice. The phases observed in the degraded areas of QWs contain voids partly filled with crystalline In and amorphous material, surrounded by the rim of high In-content In x Ga1–x N or pure InN; the remaining QW between the voids contains residual amount of In. In the case of the In x Ga1–x N QWs deposited on the GaN layer doped to n-type or on unintentionally doped GaN, we observe a preferential degradation of the first grown QW, while doping of the underlying GaN layer with Mg prevents the degradation of the closest In x Ga1–x N QW. The reduction in the metal vacancy concentration in the In x Ga1–x N QWs and their surroundings is crucial for making them more resistant to thermal degradation.

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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.

The current-voltage characteristics of planar Ni/Au Schottky diodes fabricated on top of AlGaN/GaN structures with two different surface miscut, 0.5 and 28-off, were measured at elevated temperatures of up to 580 K and then discussed. The Schottky contact parameters, such as ideality factor (n) and barrier height (w b ), were extracted by a commonly used thermionic emission approach, combined with Norde's method. In this study, we show that the temperature shift of the Schottky barrier height for a structure with 0.58-off is equal to À0.5V/100 K, which is close to the value obtained for the temperature dependence of the energy band gap for GaN. We found that for both types of structures the ideality factor decreases with the temperature increase, while the barrier height increases. Finally, we observed some differences in the leakage current mechanism and thermionic behavior, which we attribute to differences in surface homogeneity of diodes fabricated on different surface miscut.

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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.

We investigate the morphology and charge distribution at the (001)-diamond/BN heteropolar junctions of the cubic materials. Our investigations are based on the first principles calculations in the framework of the density functional theory. These studies reveal that reconstruction of the interface leads to possible charge compensation at the interface and increases also the stability of the junction in comparison to the abrupt interfaces.

We report on vertical n-GaN high voltage Schottky diodes grown by metal organic chemical vapour deposition and hydride vapour phase epitaxy on conductive ammono-GaN substrate. The thermionic emission current model has been applied for diodes analysis and parameters extraction. Finally, we demonstrate that breakdown voltage as high as 670 V for such structures can be achieved.