The significant inversion symmetry breaking specific to wurtzite semiconductors, and the associated spontaneous electrical polarization, lead to outstanding features such as high density of carriers at the GaN/(Al,Ga)N interface—exploited in high-power/high-frequency electronics—and piezoelectric capabilities serving for nanodrives, sensors and energy harvesting devices. Here we show that the multifunctionality of nitride semiconductors encompasses also a magnetoelectric effect allowing to control the magnetization by an electric field. We first demonstrate that doping of GaN by Mn results in a semi-insulating material apt to sustain electric fields as high as 5 MV cm−1. Having such a material we find experimentally that the inverse piezoelectric effect controls the magnitude of the single-ion magnetic anisotropy specific to Mn3+ ions in GaN. The corresponding changes in the magnetization can be quantitatively described by a theory developed here.

In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.

In the paper, the results of technological investigations on planar optical waveguides based on high band gap oxide semiconductors were presented. Investigations concerned the technologies of depositing very thin layers of: zinc oxide ZnO, titanium dioxide TiO2 and tin dioxide SnO2 on substrates of quartz glass plates. There were investigated both morphological structures of the produced layers and their optical properties. The paper also presents investigations on the technology of input-output light systems in the Bragg grating structures.

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Examples are presented that application of amorphous Al x O y nucleation layer is an efficient way of controlling spatial distribution of GaN nanowires grown by plasma-assisted molecular beam epitaxy. On GaN/sapphire substrates Al x O y stripes induce formation of GaN nanowires while a compact GaN layer is formed outside the stripes. We show that the ratio of nanowire length h to the thickness of the compact layer d can be tailored by adjusting impinging gallium and nitrogen fluxes. Calculations of the h/d aspect ratio were performed taking into account dependence of nanowire incubation time on the growth parameters. In agreement with calculations we found that the value of h/d ratio can be increased by increasing the N/Ga flux ratio in the way that the N-limited growth regime determines nanowire axial growth rate while growth of compact layer remains Ga-limited. This ensures the highest value of the h/d aspect ratio. Local modification of GaN growth kinetics caused by surface diffusion of Ga adatoms through the boundary separating the Al x O y stripe and the GaN/sapphire substrate is discussed. We show that during the nanowire incubation period gallium is transported out of the Al x O y stripe, which delays nanowire nucleation onset and leads to reduced length of GaN nanowires in the vicinity of the stripe edge. Simultaneously the growth on the GaN/sapphire substrate is locally enhanced, so the planar GaN layers adopts a typical edge shape of mesa structures grown by selective area growth. Ga diffusion length on a-Al x O y surface of ∼500 nm is inferred from our results.

Abstract. The paper presents the results of characterization of MOS structures with aluminum oxide layer deposited by ALD method on silicon carbide substrates. The effect of the application of thin SiO 2 buffer layer on the electrical properties of the MOS structures with Al 2 O 3 layer has been examined. Critical electric field values at the level of 7.5-8 MV/cm were obtained. The use of 5 nm thick SiO 2 buffer layer caused a decrease in the leakage current of the gate by more than two decade of magnitude. Evaluated density of trap states near the conduction band of silicon carbide in Al 2 O 3 /4H-SiC MOS is about of 1x10 13 eV -1 cm -2 . In contrast, the density of the trap states in the Al 2 O 3 /SiO 2 /4H-SiC structure is lower about of one decade of magnitude i.e. 1x1012 eV -1 cm -2 . A remarkable change in the MOS structure is also a decrease of density of electron traps located deeply in the 4H-SiC conduction band below detection limit due to using of the SiO 2 buffer layer.Key words: aluminum oxide, MOS, silicon carbide, 4H-SiC, high-κ dielectrics. Characterization of Al Experimental detailsMOS structures used in this study were fabricated on low-resistivity 4H-SiC substrates (n ~ 5×10 18 cm -3 ) with n-type (n ~ 5×10 ), 10 μm thick epitaxial layer. Prior to the MOS fabrication the substrates were cleaned in organic solvents and dipped in 10% HF solution to remove the native oxide. The nickel layer was sputtered on the backside and annealed (Ar, 1050°C) to form an ohmic contact. Two kinds of samples were fabricated. On one part of samples, 5 nm SiO 2 buffer layer was fabricated by PECVD using SiH 4 and N 2 O plasma. Afterwards, a 50 nm layer of Al 2 O 3 was deposited on all samples by ALD. Al 2 O 3 layers were deposited at 200°C using trimethylaluminium (TMA) and water vapor (H 2 O) as Al and O precursors, respectively. Finally, a top layer of Ti/Al gate electrode (φ = 200 µm) was deposited on top of Al 2 O 3 by sputtering and patterned by lift-off technique. A schematic sketch of fabricated Al 2 O 3 /4H-SiC and Al 2 O 3 /SiO 2 /4H-SiC structures is presented in Fig. 1.

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