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.

The fabrication of low-resistance and thermal stable ohmic contacts is important for realization of reliable SiC devices. For then-type SiC, Ni-based metallization is most commonly used for Schottky and ohmic contacts. Many experimental studies have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain the Schottky to ohmic transition for Ni/SiC contacts. In the present review, we summarize the last key results on the matter and post open questions concerning the unclear issues of ohmic contacts ton-type SiC. Analysis of the literature data and our own experimental observations have led to the conclusion that the annealing at high temperature leads to the preferential orientation of silicide at the heterointerface (0001)SiC//(013)δ-Ni2Si. Moreover, we may conclude that onlyδ-Ni2Si grains play a key role in determining electrical transport properties at the contact/SiC interface. Finally, we show that the diffusion barriers with free diffusion path microstructure can improve thermal stability of metal-SiC ohmic contacts for high-temperature electronics.

Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb0.92Eu0.08Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in 2e 2 /h units, despite of significant amount of charged defects in the vicinity of the constriction. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.

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Recent advances in the technology and understanding of ohmic contacts to GaAs are presented. The paper emphasizes the reactions at the metal/GaAs interface and the structural factors which govern its electrical behavior and long-term stability. Results on the optimization of conventional gold-based ohmic contacts together with recent achievements in the technology of non-alloyed.contacts are overviewed.PACS numbers: 73.40Ns Criteria for a good ohmic contactModern device concepts strongly depend on reliable and well-controlled electrical contacts through which one has to communicate with the interior of the device from the outside world. In particular, micron and submicron size Ill-V devices can be fully exploited only with adequate ohmic contacts. In addition to a wide variety of device and circuit applications, good quality ohmic contacts are required for investigating the physical and electrical properties of bulk materials and related III-V heterostructures. Consequently, much attention has been recently devoted to the development of ohmic contacts to III-V materials, and the research area include both, the fundamental behavior of metal/semiconductor contacts and the new techniques for improving the properties of ohmic contacts [1][2][3][4][5][6][7].The purpose of this paper is to bring together much of the fundamental and practical knowledge on the formation of ohmic contacts to GaAs. First, we give brief overview of the requirements for ohmic contacts in modern GaAs devices. Next, we shall comment on the actual state of understanding of the formation of potential barriers developing at metal/GaAs interfaces. While the detailed discussion of theories of metal/GaAs interface is beyond the scope of this article, basic concepts applicable to fabricate low-resistance contacts will be provided. The main part of the paper is devoted to up-todate approaches in the fabrication of ohmic contacts. We shall emphasize the reactions at the metal/semiconductor interface and the stuctural factors which govern its electrical behavior and long-term stability. Key technological issues of advanced contact technology will be given in Sec. 4.The main constraint on the choice of material for an ohmic contact is to ensure that it has the correct electrical properties. They are characterized by the (491)